CN114567432B

CN114567432B - Method and apparatus for calibrating unequal-arm interferometers in quantum communication systems

Info

Publication number: CN114567432B
Application number: CN202210191321.9A
Authority: CN
Inventors: 张建; 陈柳平; 付仁清; 刘亚龙
Original assignee: Guokaike Quantum Technology Beijing Co Ltd
Current assignee: Guokaike Quantum Technology Beijing Co Ltd
Priority date: 2022-03-01
Filing date: 2022-03-01
Publication date: 2023-08-18
Anticipated expiration: 2042-03-01
Also published as: CN114567432A

Abstract

The present invention provides methods and apparatus for calibrating an unequal-arm interferometer in a quantum communication system, the methods comprising: outputting light pulses via the first unequal arm interferometer to the second unequal arm interferometer; monitoring the single photon counts detected at the output of the second unequal arm interferometer; in response to the detected single photon count not reaching the interference threshold, maintaining the detected single photon count at the interference threshold by adjusting a phase modulation voltage applied by the phase shifter to the long arm; monitoring the phase modulation voltage during the adjusting of the phase modulation voltage; in response to the phase modulation voltage reaching a limit value of a voltage modulation range of the phase shifter, the phase shifter is caused to adjust the phase modulation voltage in a direction opposite to the limit value by the cooling fin applying a temperature disturbance to the short arm. The invention can greatly improve the adaptability of the unequal-arm interferometer in the quantum communication system to the surrounding environment, so that the bit rate of the quantum communication system is more efficient, stable and reliable.

Description

Method and apparatus for calibrating unequal-arm interferometers in quantum communication systems

Technical Field

The present invention relates to the field of quantum communication technology, and in particular, to a method and apparatus for calibrating an inequality arm interferometer in a quantum communication system.

Background

Currently, three coding modes of polarization coding, phase coding and time-phase coding are mainly adopted in a quantum communication system (such as a quantum key distribution system), wherein the phase coding and the time-phase coding both need to be coded and decoded by using different-arm interferometers. However, the interference effect of the unequal-arm interferometer is easily deteriorated by the surrounding environment, which may result in an increase in the error rate of the quantum communication system, and thus, the bit rate of the quantum communication system is significantly reduced.

Therefore, improving the adaptability of the unequal arm interferometer to the surrounding environment to ensure the stability of the interference effect of the unequal arm interferometer is a problem to be solved.

Disclosure of Invention

It is an object of the present invention to provide a method and apparatus for calibrating an unequal-arm interferometer in a quantum communication system.

According to an aspect of the present invention, there is provided a method for calibrating an unequal-arm interferometer in a quantum communication system, the method comprising: outputting light pulses via a first unequal arm interferometer to a second unequal arm interferometer, wherein the first unequal arm interferometer is included at a transmitting end of the quantum communication system and the second unequal arm interferometer is included at a receiving end of the quantum communication system; monitoring a change in the single photon count detected at the output of the second unequal arm interferometer; responsive to the detected single photon count not reaching an interference threshold corresponding to an optimal interference condition, maintaining the detected single photon count at the interference threshold by adjusting a phase modulation voltage applied to a long arm of the second unequal arm interferometer by a phase shifter on the long arm of the second unequal arm interferometer; monitoring a change in the phase modulation voltage during the adjusting of the phase modulation voltage; in response to the phase modulation voltage reaching a limit value of a voltage modulation range of the phase shifter, applying a temperature disturbance to a short arm of the second unequal arm interferometer by a refrigeration plate on the short arm of the second unequal arm interferometer, causing the phase shifter to adjust the phase modulation voltage in a direction opposite the limit value.

According to one embodiment of the invention, the optimal interference condition includes the same optical path difference between the long and short arms of the first unequal arm interferometer as the second unequal arm interferometer.

According to another aspect of the present invention, there is provided a method for calibrating an unequal-arm interferometer in a quantum communication system, the method comprising: outputting light pulses via a first unequal arm interferometer to a second unequal arm interferometer, wherein the first unequal arm interferometer is included at a transmitting end of the quantum communication system and the second unequal arm interferometer is included at a receiving end of the quantum communication system; monitoring a change in the single photon count detected at the output of the second unequal arm interferometer; responsive to the detected single photon count not reaching an interference threshold corresponding to an optimal interference condition, maintaining the detected single photon count at the interference threshold by adjusting a phase modulation voltage applied to a long arm of the first unequal arm interferometer by a phase shifter on the long arm of the first unequal arm interferometer; monitoring a change in the phase modulation voltage during the adjusting of the phase modulation voltage; in response to the phase modulation voltage reaching a limit value of a voltage modulation range of the phase shifter, a temperature disturbance is applied to a short arm of the first unequal arm interferometer by a refrigeration plate on the short arm of the first unequal arm interferometer, causing the phase shifter to adjust the phase modulation voltage in a direction opposite the limit value.

According to another aspect of the present invention, there is provided a method for calibrating an unequal-arm interferometer in a quantum communication system, the method comprising: outputting light pulses via a first unequal arm interferometer to a second unequal arm interferometer, wherein the first unequal arm interferometer is included at a transmitting end of the quantum communication system and the second unequal arm interferometer is included at a receiving end of the quantum communication system; monitoring a change in the single photon count detected at the output of the second unequal arm interferometer; responsive to the detected single photon count not reaching an interference threshold corresponding to an optimal interference condition, maintaining the detected single photon count at the interference threshold by adjusting a phase modulation voltage applied to a long arm of the second unequal arm interferometer by a phase shifter on the long arm of the second unequal arm interferometer; monitoring a change in the phase modulation voltage during the adjusting of the phase modulation voltage; in response to the phase modulation voltage reaching a limit value of a voltage modulation range of the phase shifter, a temperature disturbance is applied to a short arm of the first unequal arm interferometer by a refrigeration plate on the short arm of the first unequal arm interferometer, causing the phase shifter to adjust the phase modulation voltage in a direction opposite the limit value.

According to another aspect of the present invention, there is provided a method for calibrating an unequal-arm interferometer in a quantum communication system, the method comprising: outputting light pulses via a first unequal arm interferometer to a second unequal arm interferometer, wherein the first unequal arm interferometer is included at a transmitting end of the quantum communication system and the second unequal arm interferometer is included at a receiving end of the quantum communication system; monitoring a change in the single photon count detected at the output of the second unequal arm interferometer; responsive to the detected single photon count not reaching an interference threshold corresponding to an optimal interference condition, maintaining the detected single photon count at the interference threshold by adjusting a phase modulation voltage applied to a long arm of the first unequal arm interferometer by a phase shifter on the long arm of the first unequal arm interferometer; monitoring a change in the phase modulation voltage during the adjusting of the phase modulation voltage; in response to the phase modulation voltage reaching a limit value of a voltage modulation range of the phase shifter, applying a temperature disturbance to a short arm of the second unequal arm interferometer by a refrigeration plate on the short arm of the second unequal arm interferometer, causing the phase shifter to adjust the phase modulation voltage in a direction opposite the limit value.

According to another aspect of the present invention there is provided an apparatus for calibrating an unequal-arm interferometer in a quantum communication system, the apparatus comprising: an optical pulse output unit configured to output an optical pulse to a second unequal arm interferometer via a first unequal arm interferometer, wherein the first unequal arm interferometer is included at a transmitting end of the quantum communication system and the second unequal arm interferometer is included at a receiving end of the quantum communication system; a single photon count monitoring unit configured to monitor a change in single photon count detected at an output of the second unequal arm interferometer; a phase modulation voltage adjustment unit configured to maintain the detected single photon count at an interference threshold by adjusting a phase modulation voltage applied to a long arm of the second unequal arm interferometer by a phase shifter on the long arm of the second unequal arm interferometer in response to the detected single photon count not reaching the corresponding interference threshold under an optimal interference condition; a phase modulation voltage monitoring unit configured to monitor a change in the phase modulation voltage during adjustment of the phase modulation voltage; a temperature disturbance limiting unit configured to apply a temperature disturbance to a short arm of the second unequal arm interferometer by a refrigerating sheet on the short arm of the second unequal arm interferometer in response to the phase modulation voltage reaching a limit value of a voltage modulation range of the phase shifter, causing the phase shifter to adjust the phase modulation voltage in a direction opposite to the limit value.

According to another aspect of the present invention there is provided an apparatus for calibrating an unequal-arm interferometer in a quantum communication system, the apparatus comprising: an optical pulse output unit configured to output an optical pulse to a second unequal arm interferometer via a first unequal arm interferometer, wherein the first unequal arm interferometer is included at a transmitting end of the quantum communication system and the second unequal arm interferometer is included at a receiving end of the quantum communication system; a single photon count monitoring unit configured to monitor a change in single photon count detected at an output of the second unequal arm interferometer; a phase modulation voltage adjustment unit configured to maintain the detected single photon count at an interference threshold by adjusting a phase modulation voltage applied to a long arm of the first unequal arm interferometer by a phase shifter on the long arm of the first unequal arm interferometer in response to the detected single photon count not reaching the corresponding interference threshold under an optimal interference condition; a phase modulation voltage monitoring unit configured to monitor a change in the phase modulation voltage during adjustment of the phase modulation voltage; a temperature disturbance limiting unit configured to apply a temperature disturbance to a short arm of the first unequal arm interferometer by a refrigerating sheet on the short arm of the first unequal arm interferometer in response to the phase modulation voltage reaching a limit value of a voltage modulation range of the phase shifter, causing the phase shifter to adjust the phase modulation voltage in a direction opposite to the limit value.

According to another aspect of the present invention there is provided an apparatus for calibrating an unequal-arm interferometer in a quantum communication system, the apparatus comprising: an optical pulse output unit configured to output an optical pulse to a second unequal arm interferometer via a first unequal arm interferometer, wherein the first unequal arm interferometer is included at a transmitting end of the quantum communication system and the second unequal arm interferometer is included at a receiving end of the quantum communication system; a single photon count monitoring unit configured to monitor a change in single photon count detected at an output of the second unequal arm interferometer; a phase modulation voltage adjustment unit configured to maintain the detected single photon count at an interference threshold by adjusting a phase modulation voltage applied to a long arm of the second unequal arm interferometer by a phase shifter on the long arm of the second unequal arm interferometer in response to the detected single photon count not reaching the corresponding interference threshold under an optimal interference condition; a phase modulation voltage monitoring unit configured to monitor a change in the phase modulation voltage during adjustment of the phase modulation voltage; a temperature disturbance limiting unit configured to apply a temperature disturbance to a short arm of the first unequal arm interferometer by a refrigerating sheet on the short arm of the first unequal arm interferometer in response to the phase modulation voltage reaching a limit value of a voltage modulation range of the phase shifter, causing the phase shifter to adjust the phase modulation voltage in a direction opposite to the limit value.

According to another aspect of the present invention there is provided an apparatus for calibrating an unequal-arm interferometer in a quantum communication system, the apparatus comprising: an optical pulse output unit configured to output an optical pulse to a second unequal arm interferometer via a first unequal arm interferometer, wherein the first unequal arm interferometer is included at a transmitting end of the quantum communication system and the second unequal arm interferometer is included at a receiving end of the quantum communication system; a single photon count monitoring unit configured to monitor a change in single photon count detected at an output of the second unequal arm interferometer; a phase modulation voltage adjustment unit configured to maintain the detected single photon count at an interference threshold by adjusting a phase modulation voltage applied to a long arm of the first unequal arm interferometer by a phase shifter on the long arm of the first unequal arm interferometer in response to the detected single photon count not reaching the corresponding interference threshold under an optimal interference condition; a phase modulation voltage monitoring unit configured to monitor a change in the phase modulation voltage during adjustment of the phase modulation voltage; a temperature disturbance limiting unit configured to apply a temperature disturbance to a short arm of the second unequal arm interferometer by a refrigerating sheet on the short arm of the second unequal arm interferometer in response to the phase modulation voltage reaching a limit value of a voltage modulation range of the phase shifter, causing the phase shifter to adjust the phase modulation voltage in a direction opposite to the limit value.

According to another aspect of the invention there is provided a computer readable storage medium storing a computer program which, when executed by a processor, implements a method for calibrating an unequal-arm interferometer in a quantum communication system as described previously.

According to another aspect of the present invention, there is provided a computer apparatus including: a processor; a memory storing a computer program which, when executed by a processor, implements a method for calibrating an unequal-arm interferometer in a quantum communication system as described previously.

The method and the device for calibrating the unequal-arm interferometer in the quantum communication system can greatly improve the adaptability of the unequal-arm interferometer in the quantum communication system to the surrounding environment so as to ensure the stability of the interference effect of the unequal-arm interferometer in the quantum communication system, and the bit rate of the quantum communication system is more efficient, stable and reliable.

Drawings

The above objects and features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.

Fig. 1A shows a schematic diagram of a quantum communication system in the related art.

Fig. 1B shows a schematic graph of the optical path difference between the long and short arms of the unequal arm interferometer by adjusting the phase modulation voltage applied by the phase shifter to the long arm of the unequal arm interferometer.

Fig. 2A shows a schematic flow diagram of a method for calibrating an unequal-arm interferometer in a quantum communication system, according to an example embodiment of the invention.

Fig. 2B shows a schematic diagram of a quantum communication system to which the method shown in fig. 2A is applied.

Fig. 3A shows another schematic flow diagram of a method for calibrating an unequal-arm interferometer in a quantum communication system, according to an example embodiment of the invention.

Fig. 3B shows another schematic diagram of a quantum communication system to which the method shown in fig. 3A is applied.

Fig. 4A shows another schematic flow diagram of a method for calibrating an unequal-arm interferometer in a quantum communication system, according to an example embodiment of the invention.

Fig. 4B shows another schematic diagram of a quantum communication system to which the method shown in fig. 4A is applied.

Fig. 5A shows another schematic flow chart of a method for calibrating an unequal-arm interferometer in a quantum communication system, according to an exemplary embodiment of the invention.

Fig. 5B shows another schematic diagram of a quantum communication system to which the method shown in fig. 5A is applied.

Fig. 6 shows a schematic block diagram of an apparatus for calibrating an unequal-arm interferometer in a quantum communication system, according to an exemplary embodiment of the invention.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Referring to FIG. 1A, in the quantum communication system shown in FIG. 1A, an unequal-arm interferometer M-Z may be included ₁ And inequality arm interferometer M-Z ₂ Wherein the unequal arms interferometer M-Z ₁ Can be included in the encoding module of the transmitting end Alice of the quantum communication system shown in fig. 1A, the unequal-arm interferometer M-Z ₂ May be included in the decoding module of the receiving end Bob of the quantum communication system shown in fig. 1A. In general, in order to prevent an increase in the error rate of a quantum communication system due to deterioration of the interference effect of an unequal-arm interferometer, the unequal-arm interferometer M-Z must be made ₁ Long arm L of (2) ₁ And a short arm L ₂ Optical path difference DeltaS between ₁ And inequality arm interferometer M-Z ₂ Long arm L of (2) ₃ And a short arm L ₄ Optical path difference DeltaS between ₂ To be consistent, to ensure that the quantum communication system obtains the optimal interference effect expected, and the interference device M-Z is arranged on different arms ₂ The single photon count detected at the output of (c) will be maximized. In other words, under optimal interference conditions, the unequal arm interferometers M-Z ₁ Long arm L of (2) ₁ And a short arm L ₂ Optical path difference DeltaS between ₁ Should be compatible with inequality arm interferometers M-Z ₂ Long arm L of (2) ₃ And a short arm L ₃ Optical path difference DeltaS between ₂ The same applies. However, with changes in the surrounding environment (such as temperature, vibration, etc.), the unequal arm interferometer M-Z ₁ Long arm L of (2) ₁ And a short arm L ₂ Optical path difference DeltaS between ₁ And inequality arm interferometer M-Z ₂ Long arm L of (2) ₃ And a short arm L ₄ Optical path difference DeltaS between ₂ And also changes, so that it is difficult to always keep the two consistent.

In order to improve the adaptability of the unequal arm interferometer in the quantum communication system to the surrounding environment, ensure the stability of the interference effect of the unequal arm interferometer and improve the code rate of the quantum communication system, a phase shifter can be arranged on the long arm of the unequal arm interferometer, the phase shifter can change the phase modulation voltage applied to the long arm of the unequal arm interferometer along with the change of the surrounding environment, and the adjustment of the phase modulation voltage can realize the fine adjustment of the optical path difference between the long arm and the short arm of the unequal arm interferometer, so that the optical path difference between the long arm and the short arm of the unequal arm interferometer included in the transmitting end and the optical path difference between the long arm and the short arm of the unequal arm interferometer included in the receiving end are always consistent.

Referring to FIG. 1B, the horizontal axis characterizes the phase modulation voltage V applied by the phase shifter to the long arm of the unequal arm interferometer ₀ The vertical axis characterizes the amount of change ζ in optical path difference between the long and short arms of the unequal arm interferometer. It can be seen that the amount of change ζ in the optical path difference between the long and short arms of the unequal arm interferometer can be a function of the phase modulation voltage V ₀ Is periodically varied between + -A. Thus, the optical path difference between the long and short arms of the unequal arm interferometer may periodically follow the phase modulation voltage V ₀ Is increased with the increase of the phase modulation voltage V ₀ Is decreased by an increase in (c). Conversely, the optical path difference between the long and short arms of the unequal arm interferometer may also be periodically dependent on the phaseBit modulation voltage V ₀ Increases with decreasing amplitude of the phase modulation voltage V ₀ Is reduced by the reduction of (2).

However, in some cases, the voltage V is modulated for phase ₀ May exceed the limit value of the voltage modulation range of the phase shifter (V as shown in FIG. 1B _max Or V _min ) This can cause the quantum communication system to restart, interrupting the operation of the quantum communication system, resulting in unstable system operation and inability to continue code formation.

In view of the foregoing, the present invention provides a method for calibrating an unequal-arm interferometer in a quantum communication system.

Fig. 2A shows a schematic flow diagram of a method for calibrating an unequal-arm interferometer in a quantum communication system, according to an example embodiment of the invention. Fig. 2B shows a schematic diagram of a quantum communication system to which the method shown in fig. 2A is applied.

Referring to fig. 2A, the method shown in fig. 2A may include the following steps.

In step 201, a plurality of different arm interferometers M-Z may be used ₁ Toward inequality arm interferometer M-Z ₂ Outputting light pulses, wherein the unequal-arm interferometer M-Z ₁ May include an emitter Alice, an inequality arm interferometer M-Z in the quantum communication system shown in fig. 2B ₂ May be included at the receiving end Bob of the quantum communication system shown in fig. 2B.

At step 202, the interferometer M-Z in the unequal arms may be monitored ₂ A change in the single photon count detected at the output of (a).

At step 203, the unequal arm interferometer M-Z may be adjusted in response to the single photon count detected at step 202 not reaching the corresponding interference threshold under optimal interference conditions ₂ Long arm L of (2) ₃ The upper phase shifter FPS is directed to the unequal arm interferometer M-Z ₂ Long arm L of (2) ₃ Applied phase modulation voltage V ₀ The detected single photon count is maintained at the interference threshold.

At step 204, the phase modulation voltage V may be adjusted ₀ During which the phase modulation voltage V is monitored ₀ Is a variation of (c).

In step 205, the voltage V may be modulated in response to the phase ₀ Reaching the limit value of the voltage modulation range of the phase shifter FPS (V as shown in fig. 1B _max Or V _min ) By means of an inequality arm interferometer M-Z ₂ Short arm L of (2) ₄ TEC of upper refrigerating plate faces to unequal arm interferometer M-Z ₂ Short arm L of (2) ₄ Applying a temperature disturbance to adjust the phase-modulated voltage V in a direction opposite to the limit value by the phase shifter FPS ₀ 。

In one example, when the unequal arms interferometer M-Z ₁ Long arm L of (2) ₁ And a short arm L ₂ Optical path difference DeltaS between ₁ When increasing, the unequal arm interferometer M-Z can be increased ₂ Long arm L of (2) ₃ The upper phase shifter FPS is directed to the unequal arm interferometer M-Z ₂ Long arm L of (2) ₃ Applied phase modulation voltage V ₀ To make the unequal arm interferometer M-Z ₂ Long arm L of (2) ₃ The optical path length is lengthened to increase the unequal-arm interferometer M-Z ₂ Long arm L of (2) ₃ And a short arm L ₄ Optical path difference DeltaS between ₂ . However, when the phase modulating voltage V ₀ Reaching the limit value V of the voltage modulation range of the phase shifter _max When passing through the inequality arm interferometer M-Z ₂ Short arm L of (2) ₄ TEC of upper refrigerating plate faces to unequal arm interferometer M-Z ₂ Short arm L of (2) ₄ Applying a very small refrigeration temperature (e.g., lowering the temperature from 25 ℃ to 24.9 ℃) to cause the inequality arm interferometers M-Z ₂ Short arm L of (2) ₄ The optical path length is shortened to further increase the unequal-arm interferometer M-Z ₂ Long arm L of (2) ₃ And a short arm L ₄ Optical path difference DeltaS between ₂ . When the optical path difference DeltaS ₂ Is increased such that the optical path difference DeltaS ₂ Is greater than the optical path difference DeltaS ₁ At this time, the shifter FPS may be oriented toward the limit value V _max Adjusting the phase-modulated voltage V in the opposite direction ₀ This not only enables the shifter FPS to be coupled to the phase modulation voltage V ₀ Is limited to finding the optimal interference position within the voltage modulation range and can avoid the voltage V due to phase modulation ₀ Exceeding the limit value V of the voltage modulation range _max Resulting in an interruption of the operation of the quantum communication system.

In another example, when the unequal arms interferometer M-Z ₁ Long arm L of (2) ₁ And a short arm L ₂ Optical path difference DeltaS between ₁ When decreasing, the inequality arm interferometer M-Z can be increased ₂ Long arm L of (2) ₃ The upper phase shifter FPS is directed to the unequal arm interferometer M-Z ₂ Long arm L of (2) ₃ Applied phase modulation voltage V ₀ To make the unequal arm interferometer M-Z ₂ Long arm L of (2) ₃ The optical path length is shortened to reduce the M-Z of the unequal-arm interferometer ₂ Long arm L of (2) ₃ And a short arm L ₄ Optical path difference DeltaS between ₂ . However, when the phase modulating voltage V ₀ Reaching the limit value V of the voltage modulation range of the phase shifter _max When passing through the inequality arm interferometer M-Z ₂ Short arm L of (2) ₄ TEC of upper refrigerating plate faces to unequal arm interferometer M-Z ₂ Short arm L of (2) ₄ Applying a very small heating temperature (e.g. increasing the temperature from 25 ℃ to 25.1 ℃) to cause the inequality arm interferometers M-Z ₂ Short arm L of (2) ₄ The optical path length is lengthened to continue to reduce the unequal-arm interferometer M-Z ₂ Long arm L of (2) ₃ And a short arm L ₄ Optical path difference DeltaS between ₂ . When the optical path difference DeltaS ₂ Is reduced such that the optical path difference deltas ₂ Less than the optical path difference DeltaS ₁ At this time, the shifter FPS may be oriented toward the limit value V _max Adjusting the phase-modulated voltage V in the opposite direction ₀ This not only enables the shifter FPS to be coupled to the phase modulation voltage V ₀ Is limited to finding the optimal interference position within the voltage modulation range and can avoid the voltage V due to phase modulation ₀ Exceeding the limit value V of the voltage modulation range _max Resulting in an interruption of the operation of the quantum communication system.

In another example, when the unequal arms interferometer M-Z ₂ Long arm L of (2) ₃ And a short arm L ₄ Optical path difference DeltaS between ₂ When increasing, the unequal arm interferometer M-Z can be increased ₂ Long arm L of (2) ₃ The upper phase shifter FPS is directed to the unequal arm interferometer M-Z ₂ Long arm L of (2) ₃ Applied phase modulation voltage V ₀ To make the unequal arm interferometer M-Z ₂ Long arm L of (2) ₃ The upper optical path becomes shorterTo reduce the unequal arm interferometers M-Z ₂ Long arm L of (2) ₃ And a short arm L ₄ Optical path difference DeltaS between ₂ . However, when the phase modulating voltage V ₀ Reaching the limit value V of the voltage modulation range of the phase shifter _max When passing through the inequality arm interferometer M-Z ₂ Short arm L of (2) ₄ TEC of upper refrigerating plate faces to unequal arm interferometer M-Z ₂ Short arm L of (2) ₄ Applying a very small heating temperature (e.g. increasing the temperature from 25 ℃ to 25.1 ℃) to cause the inequality arm interferometers M-Z ₂ Short arm L of (2) ₄ The optical path length is lengthened to continue to reduce the unequal-arm interferometer M-Z ₂ Long arm L of (2) ₃ And a short arm L ₄ Optical path difference DeltaS between ₂ . When the optical path difference DeltaS ₂ Is reduced such that the optical path difference deltas ₂ Less than the optical path difference DeltaS ₁ At this time, the shifter FPS may be oriented toward the limit value V _max Adjusting the phase-modulated voltage V in the opposite direction ₀ This not only enables the shifter FPS to be coupled to the phase modulation voltage V ₀ Is limited to finding the optimal interference position within the voltage modulation range and can avoid the voltage V due to phase modulation ₀ Exceeding the limit value V of the voltage modulation range _max Resulting in an interruption of the operation of the quantum communication system.

In another example, when the unequal arms interferometer M-Z ₂ Long arm L of (2) ₃ And a short arm L ₄ Optical path difference DeltaS between ₂ When decreasing, the inequality arm interferometer M-Z can be increased ₂ Long arm L of (2) ₃ The upper phase shifter FPS is directed to the unequal arm interferometer M-Z ₂ Long arm L of (2) ₃ Applied phase modulation voltage V ₀ To make the unequal arm interferometer M-Z ₂ Long arm L of (2) ₃ The optical path length is lengthened to increase the unequal-arm interferometer M-Z ₂ Long arm L of (2) ₃ And a short arm L ₄ Optical path difference DeltaS between ₂ . However, when the phase modulating voltage V ₀ Reaching the limit value V of the voltage modulation range of the phase shifter _max When passing through the inequality arm interferometer M-Z ₂ Short arm L of (2) ₄ TEC of upper refrigerating plate faces to unequal arm interferometer M-Z ₂ Short arm L of (2) ₄ Applying a very small refrigeration temperature (e.g. bringing the temperature from 25 DEG CDown to 24.9 ℃ to make the unequal arm interferometer M-Z ₂ Short arm L of (2) ₄ The optical path length is shortened to further increase the unequal-arm interferometer M-Z ₂ Long arm L of (2) ₃ And a short arm L ₄ Optical path difference DeltaS between ₂ . When the optical path difference DeltaS ₂ Is increased such that the optical path difference DeltaS ₂ Is greater than the optical path difference DeltaS ₁ At this time, the shifter FPS may be oriented toward the limit value V _max Adjusting the phase-modulated voltage V in the opposite direction ₀ This not only enables the shifter FPS to be coupled to the phase modulation voltage V ₀ Is limited to finding the optimal interference position within the voltage modulation range and can avoid the voltage V due to phase modulation ₀ Exceeding the limit value V of the voltage modulation range _max Resulting in an interruption of the operation of the quantum communication system.

Similarly, the shifter FPS may also be made to face toward the limit value V _min Adjusting the phase-modulated voltage V in the opposite direction ₀ This not only enables the shifter FPS to be coupled to the phase modulation voltage V ₀ The adjustment of (2) limits the search for the optimum interference position within the voltage modulation range and can likewise be avoided by the phase modulation voltage V ₀ Exceeding the limit value V of the voltage modulation range _min Resulting in an interruption of the operation of the quantum communication system.

Therefore, using the method shown in fig. 2A, the adaptability of the unequal-arm interferometer in the quantum communication system to the surrounding environment can be improved to a great extent so as to ensure the stability of the interference effect of the unequal-arm interferometer in the quantum communication system, which makes the code rate of the quantum communication system more efficient, stable and reliable.

Fig. 3A shows another schematic flow diagram of a method for calibrating an unequal-arm interferometer in a quantum communication system, according to an example embodiment of the invention. Fig. 3B shows another schematic diagram of a quantum communication system to which the method shown in fig. 3A is applied.

Referring to fig. 3A, the method shown in fig. 3A may include the following steps.

In step 301, a sample may be obtained via an inequality arm interferometer M-Z ₁ Unequal arm interferometer M-Z ₂ Outputting light pulses, wherein the unequal-arm interferometer M-Z ₁ Can be included inEmission end Alice of quantum communication system shown in FIG. 3A, unequal-arm interferometer M-Z ₂ May be included at the receiving end Bob of the quantum communication system shown in fig. 3A.

At step 302, the interferometer M-Z in the unequal arms may be monitored ₂ A change in the single photon count detected at the output of (a).

In step 303, the unequal-arm interferometer M-Z may be adjusted in response to the detected single photon count not reaching the corresponding interference threshold under the optimal interference condition ₁ Long arm L of (2) ₁ The upper phase shifter FPS is directed to the unequal arm interferometer M-Z ₁ Long arm L of (2) ₁ Applied phase modulation voltage V ₀ The detected single photon count is maintained at the interference threshold.

At step 304, the phase modulation voltage V may be adjusted ₀ During which the phase modulation voltage V is monitored ₀ Is a variation of (c).

In step 305, a voltage V may be modulated in response to the phase ₀ Reaching the limit value of the voltage modulation range of the phase shifter FPS (V as shown in fig. 1B _max Or V _min ) By means of an inequality arm interferometer M-Z ₁ Short arm L of (2) ₂ TEC of upper refrigerating plate faces to unequal arm interferometer M-Z ₁ Short arm L of (2) ₂ Applying a temperature disturbance to adjust the phase-modulated voltage V in a direction opposite to the limit value by the phase shifter FPS ₀ 。

In one example, when the unequal arms interferometer M-Z ₁ Long arm L of (2) ₁ And a short arm L ₂ Optical path difference DeltaS between ₁ When increasing, the unequal arm interferometer M-Z can be increased ₁ Long arm L of (2) ₁ The upper phase shifter FPS is directed to the unequal arm interferometer M-Z ₁ Long arm L of (2) ₁ Applied phase modulation voltage V ₀ To make the unequal arm interferometer M-Z ₁ Long arm L of (2) ₁ The optical path length is shortened to reduce the M-Z of the unequal-arm interferometer ₁ Long arm L of (2) ₁ And a short arm L ₂ Optical path difference DeltaS between ₁ . However, when the phase modulating voltage V ₀ Reaching the limit value V of the voltage modulation range of the phase shifter _max When passing through the inequality arm interferometer M-Z ₁ Short arm L of (2) ₂ Upper making ofCold plate TEC (thermoelectric cooler) orientation unequal arm interferometer M-Z ₁ Short arm L of (2) ₂ Applying a very small heating temperature (e.g. increasing the temperature from 25 ℃ to 25.1 ℃) to cause the inequality arm interferometers M-Z ₁ Short arm L of (2) ₂ The optical path length is lengthened to continue to reduce the unequal-arm interferometer M-Z ₁ Long arm L of (2) ₁ And a short arm L ₂ Optical path difference DeltaS between ₁ . When the optical path difference DeltaS ₁ Is reduced such that the optical path difference deltas ₁ Less than the optical path difference DeltaS ₂ At this time, the shifter FPS may be oriented toward the limit value V _max Adjusting the phase-modulated voltage V in the opposite direction ₀ This not only enables the shifter FPS to be coupled to the phase modulation voltage V ₀ Is limited to finding the optimal interference position within the voltage modulation range and can avoid the voltage V due to phase modulation ₀ Exceeding the limit value V of the voltage modulation range _max Resulting in an interruption of the operation of the quantum communication system.

In another example, when the unequal arms interferometer M-Z ₁ Long arm L of (2) ₁ And a short arm L ₂ Optical path difference DeltaS between ₁ When decreasing, the inequality arm interferometer M-Z can be increased ₁ Long arm L of (2) ₁ The upper phase shifter FPS is directed to the unequal arm interferometer M-Z ₁ Long arm L of (2) ₁ Applied phase modulation voltage V ₀ To make the unequal arm interferometer M-Z ₁ Long arm L of (2) ₁ The optical path length is lengthened to increase the unequal-arm interferometer M-Z ₁ Long arm L of (2) ₁ And a short arm L ₁ Optical path difference DeltaS between ₁ . However, when the phase modulating voltage V ₀ Reaching the limit value V of the voltage modulation range of the phase shifter _max When passing through the inequality arm interferometer M-Z ₁ Short arm L of (2) ₂ TEC of upper refrigerating plate faces to unequal arm interferometer M-Z ₁ Short arm L of (2) ₂ Applying a very small refrigeration temperature (e.g., lowering the temperature from 25 ℃ to 24.9 ℃) to cause the inequality arm interferometers M-Z ₁ Short arm L of (2) ₂ The optical path length is shortened to further increase the unequal-arm interferometer M-Z ₁ Long arm L of (2) ₁ And a short arm L ₂ Optical path difference DeltaS between ₁ . When the optical path difference DeltaS ₁ Is increased by DeltaS ₁ Is greater than the optical path difference DeltaS ₂ At this time, the shifter FPS may be oriented toward the limit value V _max Adjusting the phase-modulated voltage V in the opposite direction ₀ This not only enables the shifter FPS to be coupled to the phase modulation voltage V ₀ Is limited to finding the optimal interference position within the voltage modulation range and can avoid the voltage V due to phase modulation ₀ Exceeding the limit value V of the voltage modulation range _max Resulting in an interruption of the operation of the quantum communication system.

In another example, when the unequal arms interferometer M-Z ₂ Long arm L of (2) ₃ And a short arm L ₄ Optical path difference DeltaS between ₂ When increasing, the unequal arm interferometer M-Z can be increased ₁ Long arm L of (2) ₁ The upper phase shifter FPS is directed to the unequal arm interferometer M-Z ₁ Long arm L of (2) ₁ Applied phase modulation voltage V ₀ To make the unequal arm interferometer M-Z ₁ Long arm L of (2) ₁ The optical path length is lengthened to increase the unequal-arm interferometer M-Z ₁ Long arm L of (2) ₁ And a short arm L ₂ Optical path difference DeltaS between ₁ . However, when the phase modulating voltage V ₀ Reaching the limit value V of the voltage modulation range of the phase shifter _max When passing through the inequality arm interferometer M-Z ₁ Short arm L of (2) ₂ TEC of upper refrigerating plate faces to unequal arm interferometer M-Z ₁ Short arm L of (2) ₂ Applying a very small refrigeration temperature (e.g., lowering the temperature from 25 ℃ to 24.9 ℃) to cause the inequality arm interferometers M-Z ₁ Short arm L of (2) ₂ The optical path length is shortened to further increase the unequal-arm interferometer M-Z ₁ Long arm L of (2) ₁ And a short arm L ₂ Optical path difference DeltaS between ₁ . When the optical path difference DeltaS ₁ Is increased by DeltaS ₁ Is greater than the optical path difference DeltaS ₂ At this time, the shifter FPS may be oriented toward the limit value V _max Adjusting the phase-modulated voltage V in the opposite direction ₀ This not only enables the shifter FPS to be coupled to the phase modulation voltage V ₀ Is limited to finding the optimal interference position within the voltage modulation range and can avoid the voltage V due to phase modulation ₀ Exceeding the limit value V of the voltage modulation range _max Resulting in an interruption of the operation of the quantum communication system.

In another exampleIn the case of unequal-arm interferometers M-Z ₂ Long arm L of (2) ₃ And a short arm L ₄ Optical path difference DeltaS between ₂ When decreasing, the inequality arm interferometer M-Z can be increased ₁ Long arm L of (2) ₁ The upper phase shifter FPS is directed to the unequal arm interferometer M-Z ₁ Long arm L of (2) ₁ Applied phase modulation voltage V ₀ To make the unequal arm interferometer M-Z ₁ Long arm L of (2) ₁ The optical path length is shortened to reduce the M-Z of the unequal-arm interferometer ₁ Long arm L of (2) ₁ And a short arm L ₁ Optical path difference DeltaS between ₁ . However, when the phase modulating voltage V ₀ Reaching the limit value V of the voltage modulation range of the phase shifter _max When passing through the inequality arm interferometer M-Z ₁ Short arm L of (2) ₂ TEC of upper refrigerating plate faces to unequal arm interferometer M-Z ₁ Short arm L of (2) ₂ Applying a very small heating temperature (e.g. increasing the temperature from 25 ℃ to 25.1 ℃) to cause the inequality arm interferometers M-Z ₁ Short arm L of (2) ₂ The optical path length is lengthened to continue to reduce the unequal-arm interferometer M-Z ₁ Long arm L of (2) ₁ And a short arm L ₂ Optical path difference DeltaS between ₁ . When the optical path difference DeltaS ₁ Is reduced by DeltaS ₁ Less than the optical path difference DeltaS ₂ At this time, the shifter FPS may be oriented toward the limit value V _max Adjusting the phase-modulated voltage V in the opposite direction ₀ This not only enables the shifter FPS to be coupled to the phase modulation voltage V ₀ Is limited to finding the optimal interference position within the voltage modulation range and can avoid the voltage V due to phase modulation ₀ Exceeding the limit value V of the voltage modulation range _max Resulting in an interruption of the operation of the quantum communication system.

Therefore, the method shown in fig. 3A can also greatly improve the adaptability of the unequal-arm interferometer in the quantum communication system to the surrounding environment so as to ensure the stability of the interference effect of the unequal-arm interferometer in the quantum communication system, which makes the code rate of the quantum communication system more efficient, stable and reliable.

Fig. 4A shows another schematic flow diagram of a method for calibrating an unequal-arm interferometer in a quantum communication system, according to an example embodiment of the invention. Fig. 4B shows another schematic diagram of a quantum communication system to which the method shown in fig. 4A is applied.

Referring to fig. 4A, the method shown in fig. 4A may include the following steps.

In step 401, a plurality of different arm interferometers M-Z may be used ₁ Toward inequality arm interferometer M-Z ₂ Outputting light pulses, wherein the unequal-arm interferometer M-Z ₁ May include an emitter Alice, an inequality arm interferometer M-Z in the quantum communication system shown in fig. 4B ₂ May be included at the receiving end Bob of the quantum communication system shown in fig. 4B.

In step 402, the interferometer M-Z in the unequal arms may be monitored ₂ A change in the single photon count detected at the output of (a).

In step 403, the unequal-arm interferometer M-Z may be adjusted in response to the detected single photon count not reaching the corresponding interference threshold under the optimal interference condition ₂ Long arm L of (2) ₃ The upper phase shifter FPS is directed to the unequal arm interferometer M-Z ₂ Long arm L of (2) ₃ Applied phase modulation voltage V ₀ The detected single photon count is maintained at the interference threshold.

At step 404, the phase modulation voltage V may be adjusted ₀ During which the phase modulation voltage V is monitored ₀ Is a variation of (c).

In step 405, a voltage V may be modulated in response to the phase ₀ Reaching the limit value of the voltage modulation range of the phase shifter FPS (V as shown in fig. 1B _max Or V _min ) By means of an inequality arm interferometer M-Z ₁ Short arm L of (2) ₂ TEC of upper refrigerating plate faces to unequal arm interferometer M-Z ₁ Short arm L of (2) ₂ Applying temperature disturbances to orient the shifter FPSRegulating the phase-modulated voltage V in a direction opposite to the limit value ₀ 。

In one example, when the unequal arms interferometer M-Z ₁ Long arm L of (2) ₁ And a short arm L ₂ Optical path difference DeltaS between ₁ When increasing, the unequal arm interferometer M-Z can be increased ₂ Long arm L of (2) ₃ The upper phase shifter FPS is directed to the unequal arm interferometer M-Z ₂ Long arm L of (2) ₃ Applied phase modulation voltage V ₀ To make the unequal arm interferometer M-Z ₂ Long arm L of (2) ₃ The optical path length is lengthened to increase the unequal-arm interferometer M-Z ₂ Long arm L of (2) ₃ And a short arm L ₄ Optical path difference DeltaS between ₂ . However, when the phase modulating voltage V ₀ Reaching the limit value V of the voltage modulation range of the phase shifter _max When passing through the inequality arm interferometer M-Z ₁ Short arm L of (2) ₂ TEC of upper refrigerating plate faces to unequal arm interferometer M-Z ₁ Short arm L of (2) ₂ Applying a very small heating temperature (e.g. increasing the temperature from 25 ℃ to 25.1 ℃) to cause the inequality arm interferometers M-Z ₁ Short arm L of (2) ₂ The optical path length is lengthened to reduce the unequal-arm interferometer M-Z ₁ Long arm L of (2) ₁ And a short arm L ₂ Optical path difference DeltaS between ₁ . When the optical path difference DeltaS ₁ Is reduced such that the optical path difference deltas ₁ Less than the optical path difference DeltaS ₂ At this time, the shifter FPS may be oriented toward the limit value V _max Adjusting the phase-modulated voltage V in the opposite direction ₀ This not only enables the shifter FPS to be coupled to the phase modulation voltage V ₀ Is limited to finding the optimal interference position within the voltage modulation range and can avoid the voltage V due to phase modulation ₀ Exceeding the limit value V of the voltage modulation range _max Resulting in an interruption of the operation of the quantum communication system.

In another example, when the unequal arms interferometer M-Z ₁ Long arm L of (2) ₁ And a short arm L ₂ Optical path difference DeltaS between ₁ When decreasing, the inequality arm interferometer M-Z can be increased ₂ Long arm L of (2) ₃ The upper phase shifter FPS is directed to the unequal arm interferometer M-Z ₂ Long arm L of (2) ₃ Applied phase modulation voltage V ₀ To avoidEqual arm interferometer M-Z ₂ Long arm L of (2) ₃ The optical path length is shortened to reduce the M-Z of the unequal-arm interferometer ₂ Long arm L of (2) ₃ And a short arm L ₄ Optical path difference DeltaS between ₂ . However, when the phase modulating voltage V ₀ Reaching the limit value V of the voltage modulation range of the phase shifter _max When passing through the inequality arm interferometer M-Z ₁ Short arm L of (2) ₂ TEC of upper refrigerating plate faces to unequal arm interferometer M-Z ₁ Short arm L of (2) ₂ Applying a very small refrigeration temperature (e.g., lowering the temperature from 25 ℃ to 24.9 ℃) to cause the inequality arm interferometers M-Z ₁ Short arm L of (2) ₂ The optical path length is shortened to enlarge the unequal-arm interferometer M-Z ₁ Long arm L of (2) ₁ And a short arm L ₂ Optical path difference DeltaS between ₁ . When the optical path difference DeltaS ₁ Is increased such that the optical path difference DeltaS ₁ Is greater than the optical path difference DeltaS ₂ At this time, the shifter FPS may be oriented toward the limit value V _max Adjusting the phase-modulated voltage V in the opposite direction ₀ This not only enables the shifter FPS to be coupled to the phase modulation voltage V ₀ Is limited to finding the optimal interference position within the voltage modulation range and can avoid the voltage V due to phase modulation ₀ Exceeding the limit value V of the voltage modulation range _max Resulting in an interruption of the operation of the quantum communication system.

In another example, when the unequal arms interferometer M-Z ₂ Long arm L of (2) ₃ And a short arm L ₄ Optical path difference DeltaS between ₂ When increasing, the unequal arm interferometer M-Z can be increased ₂ Long arm L of (2) ₃ The upper phase shifter FPS is directed to the unequal arm interferometer M-Z ₂ Long arm L of (2) ₃ Applied phase modulation voltage V ₀ To make the unequal arm interferometer M-Z ₂ Long arm L of (2) ₃ The optical path length is shortened to reduce the M-Z of the unequal-arm interferometer ₂ Long arm L of (2) ₃ And a short arm L ₄ Optical path difference DeltaS between ₂ . However, when the phase modulating voltage V ₀ Reaching the limit value V of the voltage modulation range of the phase shifter _max When passing through the inequality arm interferometer M-Z ₁ Short arm L of (2) ₂ TEC of upper refrigerating plate faces to unequal arm interferometer M-Z ₁ Short arm L of (2) ₂ Applying a very small refrigeration temperature (e.g., lowering the temperature from 25 ℃ to 24.9 ℃) to cause the inequality arm interferometers M-Z ₁ Short arm L of (2) ₂ The optical path length is shortened to enlarge the unequal-arm interferometer M-Z ₁ Long arm L of (2) ₁ And a short arm L ₂ Optical path difference DeltaS between ₁ . When the optical path difference DeltaS ₁ Is increased such that the optical path difference DeltaS ₁ Is greater than the optical path difference DeltaS ₂ At this time, the shifter FPS may be oriented toward the limit value V _max Adjusting the phase-modulated voltage V in the opposite direction ₀ This not only enables the shifter FPS to be coupled to the phase modulation voltage V ₀ Is limited to finding the optimal interference position within the voltage modulation range and can avoid the voltage V due to phase modulation ₀ Exceeding the limit value V of the voltage modulation range _max Resulting in an interruption of the operation of the quantum communication system.

In another example, when the unequal arms interferometer M-Z ₂ Long arm L of (2) ₃ And a short arm L ₄ Optical path difference DeltaS between ₂ When decreasing, the inequality arm interferometer M-Z can be increased ₂ Long arm L of (2) ₃ The upper phase shifter FPS is directed to the unequal arm interferometer M-Z ₂ Long arm L of (2) ₃ Applied phase modulation voltage V ₀ To make the unequal arm interferometer M-Z ₂ Long arm L of (2) ₃ The optical path length is lengthened to increase the unequal-arm interferometer M-Z ₂ Long arm L of (2) ₃ And a short arm L ₄ Optical path difference DeltaS between ₂ . However, when the phase modulating voltage V ₀ Reaching the limit value V of the voltage modulation range of the phase shifter _max When passing through the inequality arm interferometer M-Z ₁ Short arm L of (2) ₂ TEC of upper refrigerating plate faces to unequal arm interferometer M-Z ₁ Short arm L of (2) ₂ Applying a very small heating temperature (e.g. increasing the temperature from 25 ℃ to 25.1 ℃) to cause the inequality arm interferometers M-Z ₁ Short arm L of (2) ₂ The optical path length is lengthened to reduce the unequal-arm interferometer M-Z ₁ Long arm L of (2) ₁ And a short arm L ₂ Optical path difference DeltaS between ₁ . When the optical path difference DeltaS ₁ Is reduced such that the optical path difference deltas ₁ Less than the optical path difference DeltaS ₂ At this time, the shifter FPS may be oriented toward the limit value V _max Conversely, the following is trueDirectional adjustment of the phase modulation voltage V ₀ This not only enables the shifter FPS to be coupled to the phase modulation voltage V ₀ Is limited to finding the optimal interference position within the voltage modulation range and can avoid the voltage V due to phase modulation ₀ Exceeding the limit value V of the voltage modulation range _max Resulting in an interruption of the operation of the quantum communication system.

Therefore, the method shown in fig. 4A can also greatly improve the adaptability of the unequal-arm interferometer in the quantum communication system to the surrounding environment so as to ensure the stability of the interference effect of the unequal-arm interferometer in the quantum communication system, which makes the code rate of the quantum communication system more efficient, stable and reliable.

Fig. 5A shows another schematic flow chart of a method for calibrating an unequal-arm interferometer in a quantum communication system, according to an exemplary embodiment of the invention. Fig. 5B shows another schematic diagram of a quantum communication system to which the method shown in fig. 5A is applied.

Referring to fig. 5A, the method shown in fig. 5A may include the following steps.

In step 501, a plurality of different arm interferometers M-Z may be used ₁ Toward inequality arm interferometer M-Z ₂ Outputting light pulses, wherein the unequal-arm interferometer M-Z ₁ May include an emitter Alice, an inequality arm interferometer M-Z in the quantum communication system shown in fig. 5A ₂ May be included at the receiving end Bob of the quantum communication system shown in fig. 5A.

At step 502, the interferometer M-Z in the unequal arms may be monitored ₂ A change in the single photon count detected at the output of (a).

In step 503, the detection of the single photon count failure may be responded toReaching the corresponding interference threshold under the optimal interference condition by adjusting the inequality arm interferometer M-Z ₁ Long arm L of (2) ₁ The upper phase shifter FPS is directed to the unequal arm interferometer M-Z ₁ Long arm L of (2) ₁ Applied phase modulation voltage V ₀ The detected single photon count is maintained at the interference threshold.

At step 504, the phase modulation voltage V may be adjusted ₀ During which the phase modulation voltage V is monitored ₀ Is a variation of (c).

In step 505, the voltage V may be modulated in response to the phase ₀ Reaching the limit value of the voltage modulation range of the phase shifter FPS (V as shown in fig. 1B _max Or V _min ) By means of an inequality arm interferometer M-Z ₂ Short arm L of (2) ₄ TEC of upper refrigerating plate faces to unequal arm interferometer M-Z ₂ Short arm L of (2) ₄ Applying a temperature disturbance to adjust the phase-modulated voltage V in a direction opposite to the limit value by the phase shifter FPS ₀ 。

In one example, when the unequal arms interferometer M-Z ₁ Long arm L of (2) ₁ And a short arm L ₂ Optical path difference DeltaS between ₁ When increasing, the unequal arm interferometer M-Z can be increased ₁ Long arm L of (2) ₁ The upper phase shifter FPS is directed to the unequal arm interferometer M-Z ₁ Long arm L of (2) ₁ Applied phase modulation voltage V ₀ To make the unequal arm interferometer M-Z ₁ Long arm L of (2) ₁ The optical path length is shortened to reduce the M-Z of the unequal-arm interferometer ₁ Long arm L of (2) ₁ And a short arm L ₂ Optical path difference DeltaS between ₁ . However, when the phase modulating voltage V ₀ Reaching the limit value V of the voltage modulation range of the phase shifter _max When passing through the inequality arm interferometer M-Z ₂ Short arm L of (2) ₄ TEC of upper refrigerating plate faces to unequal arm interferometer M-Z ₂ Short arm L of (2) ₄ Applying a very small refrigeration temperature (e.g., lowering the temperature from 25 ℃ to 24.9 ℃) to cause the inequality arm interferometers M-Z ₂ Short arm L of (2) ₄ The optical path length is shortened to enlarge the unequal-arm interferometer M-Z ₂ Long arm L of (2) ₃ And a short arm L ₄ Optical path difference DeltaS between ₂ . When the optical path difference DeltaS ₂ Is increased such that the optical path difference DeltaS ₂ Is greater than the optical path difference DeltaS ₁ At this time, the shifter FPS may be oriented toward the limit value V _max Adjusting the phase-modulated voltage V in the opposite direction ₀ This not only enables the shifter FPS to be coupled to the phase modulation voltage V ₀ Is limited to finding the optimal interference position within the voltage modulation range and can avoid the voltage V due to phase modulation ₀ Exceeding the limit value V of the voltage modulation range _max Resulting in an interruption of the operation of the quantum communication system.

In another example, when the unequal arms interferometer M-Z ₁ Long arm L of (2) ₁ And a short arm L ₂ Optical path difference DeltaS between ₁ When decreasing, the inequality arm interferometer M-Z can be increased ₁ Long arm L of (2) ₁ The upper phase shifter FPS is directed to the unequal arm interferometer M-Z ₁ Long arm L of (2) ₁ Applied phase modulation voltage V ₀ To make the unequal arm interferometer M-Z ₁ Long arm L of (2) ₁ The optical path length is lengthened to increase the unequal-arm interferometer M-Z ₁ Long arm L of (2) ₁ And a short arm L ₂ Optical path difference DeltaS between ₁ . However, when the phase modulating voltage V ₀ Reaching the limit value V of the voltage modulation range of the phase shifter _max When passing through the inequality arm interferometer M-Z ₂ Short arm L of (2) ₄ TEC of upper refrigerating plate faces to unequal arm interferometer M-Z ₂ Short arm L of (2) ₄ Applying a very small heating temperature (e.g. increasing the temperature from 25 ℃ to 25.1 ℃) to cause the inequality arm interferometers M-Z ₂ Short arm L of (2) ₄ The optical path length is lengthened to reduce the unequal-arm interferometer M-Z ₂ Long arm L of (2) ₃ And a short arm L ₄ Optical path difference DeltaS between ₂ . When the optical path difference DeltaS ₂ Is reduced such that the optical path difference deltas ₂ Less than the optical path difference DeltaS ₁ At this time, the shifter FPS may be oriented toward the limit value V _max Adjusting the phase-modulated voltage V in the opposite direction ₀ This not only enables the shifter FPS to be coupled to the phase modulation voltage V ₀ Is limited to finding the optimal interference position within the voltage modulation range and can avoid the voltage V due to phase modulation ₀ Exceeding the limit value V of the voltage modulation range _max Resulting in the operation of a quantum communication systemIs not interrupted.

In another example, when the unequal arms interferometer M-Z ₂ Long arm L of (2) ₃ And a short arm L ₄ Optical path difference DeltaS between ₂ When increasing, the unequal arm interferometer M-Z can be increased ₁ Long arm L of (2) ₁ The upper phase shifter FPS is directed to the unequal arm interferometer M-Z ₁ Long arm L of (2) ₁ Applied phase modulation voltage V ₀ To make the unequal arm interferometer M-Z ₁ Long arm L of (2) ₁ The optical path length is lengthened to increase the unequal-arm interferometer M-Z ₁ Long arm L of (2) ₁ And a short arm L ₂ Optical path difference DeltaS between ₁ . However, when the phase modulating voltage V ₀ Reaching the limit value V of the voltage modulation range of the phase shifter _max When passing through the inequality arm interferometer M-Z ₂ Short arm L of (2) ₄ TEC of upper refrigerating plate faces to unequal arm interferometer M-Z ₂ Short arm L of (2) ₄ Applying a very small heating temperature (e.g. increasing the temperature from 25 ℃ to 25.1 ℃) to cause the inequality arm interferometers M-Z ₂ Short arm L of (2) ₄ The optical path length is lengthened to reduce the unequal-arm interferometer M-Z ₂ Long arm L of (2) ₃ And a short arm L ₄ Optical path difference DeltaS between ₂ . When the optical path difference DeltaS ₂ Is reduced such that the optical path difference deltas ₂ Less than the optical path difference DeltaS ₁ At this time, the shifter FPS may be oriented toward the limit value V _max Adjusting the phase-modulated voltage V in the opposite direction ₀ This not only enables the shifter FPS to be coupled to the phase modulation voltage V ₀ Is limited to finding the optimal interference position within the voltage modulation range and can avoid the voltage V due to phase modulation ₀ Exceeding the limit value V of the voltage modulation range _max Resulting in an interruption of the operation of the quantum communication system.

In another example, when the unequal arms interferometer M-Z ₂ Long arm L of (2) ₃ And a short arm L ₃ Optical path difference DeltaS between ₂ When decreasing, the inequality arm interferometer M-Z can be increased ₁ Long arm L of (2) ₁ The upper phase shifter FPS is directed to the unequal arm interferometer M-Z ₁ Long arm L of (2) ₁ Applied phase modulation voltage V ₀ To make the unequal arm interferometer M-Z ₁ Long arm L of (2) ₁ Upper part of the cylinderThe optical path is shortened to reduce the M-Z of the unequal arm interferometer ₁ Long arm L of (2) ₁ And a short arm L ₂ Optical path difference DeltaS between ₁ . However, when the phase modulating voltage V ₀ Reaching the limit value V of the voltage modulation range of the phase shifter _max When passing through the inequality arm interferometer M-Z ₂ Short arm L of (2) ₄ TEC of upper refrigerating plate faces to unequal arm interferometer M-Z ₂ Short arm L of (2) ₄ Applying a very small refrigeration temperature (e.g., lowering the temperature from 25 ℃ to 24.9 ℃) to cause the inequality arm interferometers M-Z ₂ Short arm L of (2) ₄ The optical path length is shortened to enlarge the unequal-arm interferometer M-Z ₂ Long arm L of (2) ₃ And a short arm L ₄ Optical path difference DeltaS between ₂ . When the optical path difference DeltaS ₂ Is increased such that the optical path difference DeltaS ₂ Is greater than the optical path difference DeltaS ₁ At this time, the shifter FPS may be oriented toward the limit value V _max Adjusting the phase-modulated voltage V in the opposite direction ₀ This not only enables the shifter FPS to be coupled to the phase modulation voltage V ₀ Is limited to finding the optimal interference position within the voltage modulation range and can avoid the voltage V due to phase modulation ₀ Exceeding the limit value V of the voltage modulation range _max Resulting in an interruption of the operation of the quantum communication system.

Therefore, the method shown in fig. 5A can also greatly improve the adaptability of the unequal-arm interferometer in the quantum communication system to the surrounding environment so as to ensure the stability of the interference effect of the unequal-arm interferometer in the quantum communication system, which makes the code rate of the quantum communication system more efficient, stable and reliable.

Referring to fig. 6, an apparatus for calibrating an unequal arm interferometer in a quantum communication system according to an exemplary embodiment of the present invention may include an optical pulse output unit 601, a single photon count monitoring unit 602, a phase modulation voltage adjustment unit 603, a phase modulation voltage monitoring unit 604, and a temperature interference limiting unit 605.

In one example, the light pulse output unit 601 may be configured to be via an unequal arm interferometer M-Z ₁ Toward inequality arm interferometer M-Z ₂ Outputting light pulses, wherein the unequal-arm interferometer M-Z ₁ May include an emitter Alice, an inequality arm interferometer M-Z in the quantum communication system shown in fig. 2B ₂ A receiving end Bob that may be included in the quantum communication system shown in fig. 2B; the single photon count monitoring unit 602 may be configured to monitor the interferometer M-Z in the unequal arms ₂ A change in single photon count detected at the output of (2); the phase modulation voltage adjustment unit 603 may be configured to adjust the unequal arm interferometers M-Z in response to the single photon count detected at step 202 not reaching the corresponding interference threshold under optimal interference conditions ₂ Long arm L of (2) ₃ The upper phase shifter FPS is directed to the unequal arm interferometer M-Z ₂ Long arm L of (2) ₃ Applied phase modulation voltage V ₀ Maintaining the detected single photon count at an interference threshold; the phase modulation voltage monitoring unit 604 may be configured to regulate the phase modulation voltage V ₀ During which the phase modulation voltage V is monitored ₀ Is a variation of (2); the temperature disturbance limiting unit 605 may be configured to respond to the phase modulation voltage V ₀ Reaching the limit value of the voltage modulation range of the phase shifter FPS (V as shown in fig. 1B _max Or V _min ) By means of an inequality arm interferometer M-Z ₂ Short arm L of (2) ₄ TEC of upper refrigerating plate faces to unequal arm interferometer M-Z ₂ Short arm L of (2) ₄ Applying a temperature disturbance to adjust the phase-modulated voltage V in a direction opposite to the limit value by the phase shifter FPS ₀ 。

In another example, the light pulse output unit 601 may be configured to be via an inequality arm interferometer M-Z ₁ To unequal arm stemsInterferometer M-Z ₂ Outputting light pulses, wherein the unequal-arm interferometer M-Z ₁ May include an emitter Alice, an inequality arm interferometer M-Z in the quantum communication system shown in fig. 3A ₂ A receiving end Bob that may be included in the quantum communication system shown in fig. 3A; the single photon count monitoring unit 602 may be configured to monitor the interferometer M-Z in the unequal arms ₂ A change in single photon count detected at the output of (2); the phase modulation voltage adjustment unit 603 may be configured to adjust the unequal arm interferometer M-Z in response to the detected single photon count not reaching the corresponding interference threshold under optimal interference conditions ₁ Long arm L of (2) ₁ The upper phase shifter FPS is directed to the unequal arm interferometer M-Z ₁ Long arm L of (2) ₁ Applied phase modulation voltage V ₀ Maintaining the detected single photon count at an interference threshold; the phase modulation voltage monitoring unit 604 may be configured to regulate the phase modulation voltage V ₀ During which the phase modulation voltage V is monitored ₀ Is a variation of (2); the temperature disturbance limiting unit 605 may be configured to respond to the phase modulation voltage V ₀ Reaching the limit value of the voltage modulation range of the phase shifter FPS (V as shown in fig. 1B _max Or V _min ) By means of an inequality arm interferometer M-Z ₁ Short arm L of (2) ₂ TEC of upper refrigerating plate faces to unequal arm interferometer M-Z ₁ Short arm L of (2) ₂ Applying a temperature disturbance to adjust the phase-modulated voltage V in a direction opposite to the limit value by the phase shifter FPS ₀ 。

In another example, the light pulse output unit 601 may be configured to be via an inequality arm interferometer M-Z ₁ Unequal arm interferometer M-Z ₂ Outputting light pulses, wherein the unequal-arm interferometer M-Z ₁ May include an emitter Alice, an inequality arm interferometer M-Z in the quantum communication system shown in fig. 3A ₂ A receiving end Bob that may be included in the quantum communication system shown in fig. 3A; the single photon count monitoring unit 602 may be configured to monitor the interferometer M-Z in the unequal arms ₂ A change in single photon count detected at the output of (2); the phase modulation voltage adjustment unit 603 may be configured to adjust the inequality in response to the detected single photon count not reaching the corresponding interference threshold under the optimal interference conditionArm interferometer M-Z ₂ Long arm L of (2) ₃ The upper phase shifter FPS is directed to the unequal arm interferometer M-Z ₂ Long arm L of (2) ₃ Applied phase modulation voltage V ₀ Maintaining the detected single photon count at an interference threshold; the phase modulation voltage monitoring unit 604 may be configured to regulate the phase modulation voltage V ₀ During which the phase modulation voltage V is monitored ₀ Is a variation of (2); the temperature disturbance limiting unit 605 may be configured to respond to the phase modulation voltage V ₀ Reaching the limit value of the voltage modulation range of the phase shifter FPS (V as shown in fig. 1B _max Or V _min ) By means of an inequality arm interferometer M-Z ₁ Short arm L of (2) ₂ TEC of upper refrigerating plate faces to unequal arm interferometer M-Z ₁ Short arm L of (2) ₂ Applying a temperature disturbance to adjust the phase-modulated voltage V in a direction opposite to the limit value by the phase shifter FPS ₀ 。

In another example, the light pulse output unit 601 may be configured to be via an inequality arm interferometer M-Z ₁ Unequal arm interferometer M-Z ₂ Outputting light pulses, wherein the unequal-arm interferometer M-Z ₁ May include an emitter Alice, an inequality arm interferometer M-Z in the quantum communication system shown in fig. 3A ₂ A receiving end Bob that may be included in the quantum communication system shown in fig. 3A; the single photon count monitoring unit 602 may be configured to monitor the interferometer M-Z in the unequal arms ₂ A change in single photon count detected at the output of (2); the phase modulation voltage adjustment unit 603 may be configured to adjust the unequal arm interferometer M-Z in response to the detected single photon count not reaching the corresponding interference threshold under optimal interference conditions ₁ Long arm L of (2) ₁ The upper phase shifter FPS is directed to the unequal arm interferometer M-Z ₁ Long arm L of (2) ₁ Applied phase modulation voltage V ₀ Maintaining the detected single photon count at an interference threshold; the phase modulation voltage monitoring unit 604 may be configured to regulate the phase modulation voltage V ₀ During which the phase modulation voltage V is monitored ₀ Is a variation of (2); the temperature disturbance limiting unit 605 may be configured to respond to the phase modulation voltage V ₀ Reaching the limit value of the voltage modulation range of the phase shifter FPS (V as shown in fig. 1B _max Or V _min ) By means of an inequality arm interferometer M-Z ₂ Short arm L of (2) ₄ TEC of upper refrigerating plate faces to unequal arm interferometer M-Z ₂ Short arm L of (2) ₄ Applying a temperature disturbance to adjust the phase-modulated voltage V in a direction opposite to the limit value by the phase shifter FPS ₀ 。

Therefore, the device shown in fig. 6 can also greatly improve the adaptability of the unequal-arm interferometer in the quantum communication system to the surrounding environment so as to ensure the stability of the interference effect of the unequal-arm interferometer in the quantum communication system, which makes the code rate of the quantum communication system more efficient, stable and reliable.

Furthermore, a computer-readable storage medium storing a computer program may also be provided according to an exemplary embodiment of the present invention. The computer readable storage medium stores a computer program which, when executed by a processor, causes the processor to perform a method for calibrating an unequal-arm interferometer in a quantum communication system according to an exemplary embodiment of the invention. The computer readable recording medium is any data storage device that can store data which can be read out by a computer system. Examples of the computer-readable recording medium include: read-only memory, random access memory, compact disc read-only, magnetic tape, floppy disk, optical data storage device, and carrier waves (such as data transmission through the internet via wired or wireless transmission paths).

Furthermore, a computing device may be provided in accordance with an exemplary embodiment of the present application. The computing device includes a processor and a memory. The memory is used for storing a computer program. The computer program is executed by a processor to cause the processor to perform a computer program for a method for calibrating an unequal-arm interferometer in a quantum communication system according to an exemplary embodiment of the application.

While the application has been shown and described with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made to these embodiments without departing from the spirit and scope of the application as defined by the following claims.

Claims

1. A method for calibrating an unequal-arm interferometer in a quantum communication system, the method comprising:

outputting light pulses via a first unequal arm interferometer to a second unequal arm interferometer, wherein the first unequal arm interferometer is included at a transmitting end of the quantum communication system and the second unequal arm interferometer is included at a receiving end of the quantum communication system;

monitoring a change in the single photon count detected at the output of the second unequal arm interferometer;

responsive to the detected single photon count not reaching an interference threshold corresponding to an optimal interference condition, maintaining the detected single photon count at the interference threshold by adjusting a phase modulation voltage applied to a long arm of the second unequal arm interferometer by a phase shifter on the long arm of the second unequal arm interferometer;

Monitoring a change in the phase modulation voltage during the adjusting of the phase modulation voltage;

in response to the phase modulation voltage reaching a limit value of a voltage modulation range of the phase shifter, applying a temperature disturbance to a short arm of the second unequal arm interferometer by a refrigeration plate on the short arm of the second unequal arm interferometer, causing the phase shifter to adjust the phase modulation voltage in a direction opposite the limit value.

2. The method of claim 1, wherein the optimal interference condition comprises a same optical path difference between a long arm and a short arm of the first unequal arm interferometer as a long arm and a short arm of the second unequal arm interferometer.

3. A method for calibrating an unequal-arm interferometer in a quantum communication system, the method comprising:

Responsive to the detected single photon count not reaching an interference threshold corresponding to an optimal interference condition, maintaining the detected single photon count at the interference threshold by adjusting a phase modulation voltage applied to a long arm of the first unequal arm interferometer by a phase shifter on the long arm of the first unequal arm interferometer;

in response to the phase modulation voltage reaching a limit value of a voltage modulation range of the phase shifter, a temperature disturbance is applied to a short arm of the first unequal arm interferometer by a refrigeration plate on the short arm of the first unequal arm interferometer, causing the phase shifter to adjust the phase modulation voltage in a direction opposite the limit value.

4. A method according to claim 3, wherein the optimal interference condition comprises the same optical path difference between the long and short arms of the first unequal arm interferometer as the second unequal arm interferometer.

5. A method for calibrating an unequal-arm interferometer in a quantum communication system, the method comprising:

6. The method of claim 5, wherein the optimal interference condition comprises a same optical path difference between a long arm and a short arm of the first unequal arm interferometer as a long arm and a short arm of the second unequal arm interferometer.

7. A method for calibrating an unequal-arm interferometer in a quantum communication system, the method comprising:

8. The method of claim 7, wherein the optimal interference condition comprises a same optical path difference between a long arm and a short arm of the first unequal arm interferometer as a long arm and a short arm of the second unequal arm interferometer.

9. An apparatus for calibrating an unequal-arm interferometer in a quantum communication system, the apparatus comprising:

an optical pulse output unit configured to output an optical pulse to a second unequal arm interferometer via a first unequal arm interferometer, wherein the first unequal arm interferometer is included at a transmitting end of the quantum communication system and the second unequal arm interferometer is included at a receiving end of the quantum communication system;

a single photon count monitoring unit configured to monitor a change in single photon count detected at an output of the second unequal arm interferometer;

a phase modulation voltage adjustment unit configured to maintain the detected single photon count at an interference threshold by adjusting a phase modulation voltage applied to a long arm of the second unequal arm interferometer by a phase shifter on the long arm of the second unequal arm interferometer in response to the detected single photon count not reaching the corresponding interference threshold under an optimal interference condition;

A phase modulation voltage monitoring unit configured to monitor a change in the phase modulation voltage during adjustment of the phase modulation voltage;

a temperature disturbance limiting unit configured to apply a temperature disturbance to a short arm of the second unequal arm interferometer by a refrigerating sheet on the short arm of the second unequal arm interferometer in response to the phase modulation voltage reaching a limit value of a voltage modulation range of the phase shifter, causing the phase shifter to adjust the phase modulation voltage in a direction opposite to the limit value.

10. The apparatus of claim 9, wherein the optimal interference condition comprises a same optical path difference between a long arm and a short arm of the first unequal arm interferometer as a long arm and a short arm of the second unequal arm interferometer.

11. An apparatus for calibrating an unequal-arm interferometer in a quantum communication system, the apparatus comprising:

a phase modulation voltage adjustment unit configured to maintain the detected single photon count at an interference threshold by adjusting a phase modulation voltage applied to a long arm of the first unequal arm interferometer by a phase shifter on the long arm of the first unequal arm interferometer in response to the detected single photon count not reaching the corresponding interference threshold under an optimal interference condition;

a temperature disturbance limiting unit configured to apply a temperature disturbance to a short arm of the first unequal arm interferometer by a refrigerating sheet on the short arm of the first unequal arm interferometer in response to the phase modulation voltage reaching a limit value of a voltage modulation range of the phase shifter, causing the phase shifter to adjust the phase modulation voltage in a direction opposite to the limit value.

12. The apparatus of claim 11, wherein the optimal interference condition comprises a same optical path difference between a long arm and a short arm of the first unequal arm interferometer as a long arm and a short arm of the second unequal arm interferometer.

13. An apparatus for calibrating an unequal-arm interferometer in a quantum communication system, the apparatus comprising:

14. The apparatus of claim 13, wherein the optimal interference condition comprises a same optical path difference between a long arm and a short arm of the first unequal arm interferometer as a long arm and a short arm of the second unequal arm interferometer.

15. An apparatus for calibrating an unequal-arm interferometer in a quantum communication system, the apparatus comprising:

16. The apparatus of claim 15, wherein the optimal interference condition comprises a same optical path difference between a long arm and a short arm of the first unequal arm interferometer as a long arm and a short arm of the second unequal arm interferometer.

17. A computer readable storage medium storing a computer program, characterized in that the method for calibrating an unequal-arm interferometer in a quantum communication system according to any of claims 1 to 8 is implemented when the computer program is executed by a processor.

18. A computing device, comprising:

a processor;

memory storing a computer program which, when executed by a processor, implements the method for calibrating an unequal-arm interferometer in a quantum communication system according to any of claims 1 to 8.