WO2017092484A1

WO2017092484A1 - Method and device for forming quantum bit

Info

Publication number: WO2017092484A1
Application number: PCT/CN2016/099551
Authority: WO
Inventors: 钱懿; 冯付莱德·致衡
Original assignee: 华为技术有限公司
Priority date: 2015-12-03
Filing date: 2016-09-21
Publication date: 2017-06-08
Also published as: CN106850194A; CN106850194B

Abstract

The present invention relates to the technical field of quantum information and discloses a method and device for forming a quantum bit to solve the problem in the related art in which only certain states of a quantum bit can be formed. The device comprises: a single-photon source, a polarizer and an improved asymmetric Mach-Zehnder interferometer (AMZI) connected in sequence, wherein: the improved AMZI comprises a polarization beam splitter, a first optical waveguide, a second optical waveguide, a 3dB coupler, a phase modulator located on a transmission path formed by the first optical waveguide or the second optical waveguide, and a polarization rotator located on the transmission path formed by the first optical waveguide or the second optical waveguide; the first optical waveguide has a length greater than that of the second optical waveguide, an input of the polarization beam splitter is connected to the polarizer, two outputs of the polarization beam splitter are respectively connected to inputs of the first optical waveguide and the second optical waveguide, and outputs of the first and second optical waveguides are respectively connected to inputs of the 3dB coupler. The present invention is applied in the process of forming quantum bits.

Description

Method and device for preparing quantum bits

The present application claims priority to Chinese Patent Application No. 201510883512. filed on Dec. 3, 2015, the entire disclosure of which is hereby incorporated by reference. .

Technical field

The present invention relates to the field of quantum information technology, and in particular, to a method and an apparatus for preparing quantum bits.

Background technique

Quantum information technology originated in the 1980s and mainly includes quantum computing and quantum communication. Quantum Key Distribution (QKD) technology in quantum information technology provides physical unconditional secure information transmission capability and is considered to be the most secure encryption method. Because of this, the application of QKD technology is now more and more extensive. In the implementation of QKD technology, the premise of key distribution is to prepare quantum bits.

At present, there is provided an apparatus and method for preparing quantum bits, as shown in FIG. 1 , which specifically includes four single

photon light sources

11 , 12 , 13 and 14 , and a first optical waveguide 15 , a first optical waveguide 15 . A two-dimensional optical waveguide 16 and an Asymmetric Mach-Zehnder Interferometer (AMZI) 17. The length of the second optical waveguide 16 is greater than the length of the first optical waveguide 15; the AMZI 17 includes a third optical waveguide 171, a fourth optical waveguide 172, a phase modulator 173, two 3dB couplers 174, and a third optical waveguide 171. The length is greater than the length of the fourth optical waveguide 172, which is equivalent to the two interference arms of the AMZI; the phase modulator 173 is located on the corresponding transmission path of any one of the interference arms; the two 3dB couplers are respectively located at the two ends of the two interference arms. The working principle is specifically: a single photon pulse emitted by the single photon source 11 forms a pre-timing pulse state |F> through the first optical waveguide 15; a single photon pulse emitted by the single photon source 12 forms a pass through the second optical waveguide 16 Post-timing pulse state |S>; single photon pulse from single photon source 13 passes through AMZI 17 (phase of phase modulator is 0), and outputs quantum superposition of front and rear timing pulses

The single photon pulse emitted by the single photon source 14 passes through the AMZI (the phase of the phase modulator is π), and the quantum superposition state of the front and rear timing pulses is output.

The existing apparatus and method for preparing such quantum bits can only achieve a specific quantum bit state, and the flexibility of quantum information processing is limited.

Summary of the invention

The invention provides a method and a device for preparing quantum bits, which can prepare quantum bits of any form.

In order to achieve the above object, the present invention adopts the following technical solutions:

In a first aspect, an embodiment of the present invention provides a device for preparing a quantum bit, comprising: a single photon source, a polarizer, and a modified unequal arm Mach-Zehnder interferometer, which are sequentially connected, wherein:

The improved unequal-arm Mach-Zehnder interferometer includes a polarization beam splitter, a first optical waveguide, a second optical waveguide, a 3dB coupler, and a phase modulation on a transmission path formed by the first optical waveguide or the second optical waveguide a polarization rotator on a transmission path formed by the first optical waveguide or the second optical waveguide; a length of the first optical waveguide is greater than a length of the second optical waveguide, and an input end of the polarization beam splitter The polarizer is connected, a first output end of the polarizing beam splitter is coupled to an input end of the first optical waveguide, a second output end of the polarizing beam splitter and an input of the second optical waveguide End connection, an output end of the first optical waveguide and the second optical waveguide are respectively connected to an input end of the 3dB coupler;

The polarizer is configured to process the single photon emitted by the single photon source to output polarized light having a polarization angle of α, and the value of α ranges from 0 degrees to 360 degrees;

The polarizing beam splitter is configured to split polarized light having the polarization angle α to form polarized light of two different polarization directions;

The first optical waveguide and the second optical waveguide are configured to respectively transmit the polarized light of the two different polarization directions; wherein a polarization rotator for polarizing light transmitted along an optical waveguide corresponding to the polarization rotator The polarization angle is rotated by a first predetermined angle such that the polarization angles of the polarized light output by the first optical waveguide and the second optical waveguide are the same; a phase modulator for adjusting along the phase The phase of the polarized light transmitted by the optical waveguide corresponding to the controller is modulated by a second preset angle φ, and the second preset angle φ ranges from 0 degrees to 360 degrees;

The 3dB coupler is configured to superimpose light output by the first optical waveguide and the second optical waveguide to form a qubit.

In conjunction with the first aspect, in a first implementation of the first aspect, the polarizing beam splitter is configured to split the exiting light from the polarizer into outgoing light of a horizontal polarization direction and a vertical polarization direction.

In conjunction with the first implementation of the first aspect, in a second implementation of the first aspect, the polarization rotator is configured to rotate the polarization of the exiting light from the polarizing beam splitter by 90 degrees.

In conjunction with the first aspect, in a third implementation of the first aspect, the apparatus further includes a controller for controlling a polarization angle α of the polarized light output by the polarizer and a modulation of the phase modulator The value of the second preset angle φ is described.

In conjunction with the first aspect, or any one of the first, second, and third implementations of the first aspect, in a fourth implementation of the first aspect, the phase modulator is located in the first On the transmission path formed by the optical waveguide, the polarization rotator is located on a transmission path formed by the second optical waveguide.

In a second aspect, an embodiment of the present invention provides a method for preparing a qubit, which is applied to the apparatus of the first aspect, the method comprising:

The polarizer processes the single photon emitted by the single photon source to output polarized light having a polarization angle of α, and the value of α ranges from 0 to 360 degrees;

The polarizing beam splitter splits the polarized light having the polarization angle α to form polarized light of two different polarization directions;

The first optical waveguide and the second optical waveguide respectively transmit the polarized light of the two different polarization directions, wherein during the transmission, the polarization rotator polarizes the polarized light transmitted along the optical waveguide corresponding to the polarization rotator The angle is rotated by a first predetermined angle such that the polarization angles of the polarized light output by the first optical waveguide and the second optical waveguide are the same; the phase modulator will phase the polarized light transmitted along the optical waveguide corresponding to the phase modulator Modulating the second preset angle φ, the value of φ is 0 degrees Up to 360 degrees;

The 3dB coupler superimposes the light output by the first optical waveguide and the second optical waveguide to form a qubit.

With reference to the second aspect, in a first implementation of the second aspect, the polarizing beam splitter splits the polarized light having the polarization angle α to form polarized light of two different polarization directions, and specifically includes:

The polarization beam splitter splits the polarized light having the polarization angle α to form polarized light in the horizontal direction and polarized light in the vertical direction.

In conjunction with the first implementation of the second aspect, in a second implementation of the second aspect, when the phase modulator is located on a transmission path formed by the first optical waveguide, the polarization rotator is located in the second optical waveguide And forming, on the transmission path, the first optical waveguide transmits the polarized light in the vertical direction, and when the second optical waveguide transmits the polarized light in the horizontal direction, the quantum bits output by the 3dB coupler are before and after The qubit of the time-series pulse superposition state: cosα|F>+exp(iφ)sinα|S>, where |F> is the qubit of the pre-timing pulse state; |S> is the qubit of the post-timing pulse state.

The apparatus for preparing quantum bits provided by the embodiments of the present invention improves the conventional unequal-arm Mach-Zehnder interferometer, and replaces the first 3dB coupler of the conventional unequal-arm Mach-Zehnder interferometer with a polarization component. The beam splitter reduces the number of 3dB couplers and thus reduces line insertion loss; the polarizer between the single photon source and the modified unequal arm Mach-Zehnder interferometer can produce a single photon source when preparing the qubits The emitted single photon is processed to output polarized light of any angle; then the polarizing beam splitter is used to replace the polarization of the polarized light output by the 3dB coupler in the prior art to obtain two polarized lights of different polarization directions; The first optical waveguide and the second optical waveguide respectively transmit polarized light of two different polarization directions, and in order to ensure that the polarized light in the two directions after the splitting can interfere at the 3 dB coupler during the transmission, the polarization rotation is adopted. The polarized light in one of the directions is polarized and rotated. In addition, the phase modulator in the improved unequal-arm Mach-Zehnder interferometer can modulate the phase of the polarized light in one direction to any angle; the last 3dB coupler superimposes the two polarized lights in the same direction. Quantum bits. Because the polarizer is capable of polarizing light from a single photon source to obtain polarized light at any angle, and the phase modulator in the modified unequal arm Mach-Zehnder interferometer can achieve any angle The modulation, and thus the quantum bit preparation apparatus provided by the present invention, enables the preparation of qubits of any form.

DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the description of the prior art will be briefly described below. Obviously, the drawings in the following description are only It is a certain embodiment of the present invention, and other drawings can be obtained from those skilled in the art without any creative work.

1 is a schematic diagram of a quantum bit preparation apparatus provided by the prior art;

2 is a schematic diagram of a first qubit preparation device according to an embodiment of the present invention;

3 is a schematic diagram of a second qubit preparation device according to an embodiment of the present invention;

4 is a schematic diagram of a third quantum bit preparation apparatus according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of a method for preparing a quantum bit according to an embodiment of the present invention.

detailed description

The technical solutions in the present embodiment will be clearly and completely described in the following with reference to the drawings in the embodiments. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts are within the scope of the present invention.

An embodiment of the present invention provides a quantum bit preparation apparatus, as shown in FIG. 2, comprising: a single photon source 21, a polarizer 22, and a modified unequal arm Mach-Zehnder interferometer 23.

The single photon source is a light source for generating a single photon. In the embodiment of the present invention, the number of single photon sources is one. Polarizer is an optical device for obtaining polarized light from natural light, and the specific implementation may be a polarizing plate, a Nicol prism, etc.; the polarizer has a range of 0 to 360 degrees, That is, the polarizer can process the photons emitted by the single photon source to form polarized light of any angle. The specific structure of the single-photon source and the polarizer can be referred to the prior art, and details are not described herein again.

A conventional unequal arm Mach-Zehnder interferometer generally includes an asymmetric interference arm formed by two optical waveguides of different lengths and a 3 dB coupler located at each end of the two interference arms. The improved unequal-arm Mach-Zehnder interferometer 23 provided by the embodiment of the present invention includes a polarization beam splitter 231, a first optical waveguide 232, a second optical waveguide 233, a 3dB coupler 234, a phase modulator 235 located on a transmission path formed by the first optical waveguide or the second optical waveguide, or a first optical waveguide or a second optical waveguide A polarization rotator 236 is formed on the transmission path. The optical waveguide is a medium that transmits light, and may be an optical fiber or the like. The length of the first optical waveguide is greater than the length of the second optical waveguide, that is, the first optical waveguide forms a longer interference arm of the unequal arm Mach-Zehnder interferometer, and the second optical waveguide forms an unequal arm The shorter interference arm of the Mach-Zehnder interferometer. The phase modulator and the polarization rotator can be located on the same interference arm or on different interference arms.

Alternatively, as shown in FIG. 2, both the phase modulator and the polarization rotator are located on a transmission path formed by the first optical waveguide 232.

Optionally, as shown in FIG. 3, the phase modulator 235 is located on a transmission path formed by the first optical waveguide 232; and the polarization rotator 236 is located on a transmission path formed by the second optical waveguide 233.

Based on the above structure of the modified unequal-arm Mach-Zehnder interferometer, the connection relationship and effect between the respective elements are described below: the input end of the polarization beam splitter 231 is connected to the polarizer 22 for The outgoing light of the polarizer 22 is split into two polarized lights of different polarization directions and output through the first output end and the second output end respectively; the first output end of the polarizing beam splitter 231 and the first light The input end of the waveguide 232 is connected, and the second output end of the polarization beam splitter 231 is connected to the input end of the second optical waveguide 233. The output ends of the first optical waveguide 232 and the second optical waveguide 233 are respectively connected to the input end of the 3dB coupler 234 so that the 3dB coupler 234 performs the light output by the first optical waveguide and the second optical waveguide. Quantum bits are formed after interference. Wherein the polarization rotator on the corresponding transmission path of the first optical waveguide or the second optical waveguide is used to rotate the polarization angle of the outgoing light from the polarization beam splitter by a first predetermined angle to make the first optical waveguide and the first optical waveguide The polarization angle of the polarized light output by the two optical waveguides is the same; the phase modulator located on the corresponding transmission path of the first optical waveguide or the second optical waveguide is for modulating the phase of the outgoing light from the polarization beam splitter by a second predetermined angle φ The second preset angle φ ranges from 0 degrees to 360 degrees.

Optionally, the polarizing beam splitter is configured to split the outgoing light from the polarizer into outgoing light of a horizontal polarization direction and a vertical polarization direction, and then output through the two output ends. The first output end is used for outputting the outgoing light of the horizontal polarization direction, and correspondingly, the second output end is for outputting the output light of the vertical polarization direction. Alternatively, the first output is used to output the outgoing light in the vertical polarization direction, and the second output is The output is used to output the outgoing light in the horizontal polarization direction. Correspondingly, a polarization rotator is used for rotating the polarization angle of the outgoing light from the polarization beam splitter by 90 degrees to ensure that the polarization angles of the outgoing light output by the first optical waveguide and the second optical waveguide are the same, that is, the first light The direction in which the waveguide and the second optical waveguide output the outgoing light is the same.

The 3dB coupler is a common optic device that can couple light from several bundles of fibers to other bundles of fibers at the same wavelength, or separate light from one bundle of fibers to several bundles of fibers. in. On the other hand, it will bring about a large channel insertion loss, and the more the number of 3dB couplers, the greater the channel insertion loss. The unequal-arm Mach-Zehnder interferometer provided by the embodiment of the invention replaces the first 3dB coupler of the conventional unequal-arm Mach-Zehnder interferometer with a polarization beam splitter, reducing the number of 3dB couplers on the line , which reduces insertion loss.

It should be noted that, in the improved unequal-arm Mach-Zehnder interferometer provided by the embodiment of the present invention, the specific structure of the optical waveguide, the 3dB coupler, the polarization beam splitter, the phase modulator, the polarization rotator and the like are included. Reference may be made to the prior art, and details are not described herein again. In addition, the 3dB coupler is a 50:50 coupling ratio coupler and is therefore referred to in some literature as a 50:50 coupler or a half coupler.

It should also be noted that the connections between the various elements referred to in the embodiments of the present invention refer to connections through optical fibers or other connections commonly found in the optical arts.

In addition, in order to facilitate the adjustment of the polarization angle α and the second preset angle φ, the quantum bit preparation apparatus provided by the embodiment of the present invention, as shown in FIG. 4, further includes a controller 31 for adjusting the polarizer 22 The polarization angle α of the output polarized light and the value of the second predetermined angle φ modulated by the phase modulator 235.

In summary, the quantum bit preparation apparatus provided by the embodiment of the present invention requires only one single photon source compared to the prior art, which reduces the number of single photon sources; and the conventional unequal arm Mach Zengde The interferometer has been improved to reduce insertion loss on the line.

In conjunction with the foregoing apparatus, an embodiment of the present invention further provides a method for preparing quantum bits by using the foregoing apparatus, as shown in FIG. 5, including:

401: The polarizer processes the single photon emitted by the single photon source to output polarized light having a polarization angle of α.

Wherein, the value of α can be any angle from 0 degrees to 360 degrees, and the specific value is controlled by the controller according to requirements. The value of α affects the photon output by the polarizer, which is polarized. The probability that the beam splitter will appear in two different directions after polarization processing.

402: The polarizing beam splitter splits the polarized light having the polarization angle α to form polarized light of two different polarization directions.

403: The first optical waveguide and the second optical waveguide respectively transmit the polarized light of the two different polarization directions, wherein the polarization rotator transmits the polarized light along the optical waveguide corresponding to the polarization rotator during transmission The polarization angle is rotated by a first predetermined angle; the phase modulator modulates the phase of the polarized light transmitted along the optical waveguide corresponding to the phase modulator by a second predetermined angle φ.

Wherein, the value of φ ranges from 0 to 360 degrees, that is, the phase modulator can modulate the phase of the polarized light in one of the directions to an arbitrary angle. The specific value can be controlled by the controller by the phase modulator.

The polarization rotator rotates the polarization angle of the polarized light transmitted along the optical waveguide corresponding to the polarization rotator by a first predetermined angle in order to ensure polarization of the two beams of light output by the first optical waveguide and the second optical waveguide. The angles are the same, that is, the directions of the two beams of the first optical waveguide and the second optical waveguide are the same, so that the 3dB coupler can interfere the two beams output by the first optical waveguide and the second optical waveguide.

Optionally, in step 302, the polarizing beam splitter splits the polarized light into polarized light in a horizontal direction and polarized light in a vertical direction. Correspondingly, in step 303, the first preset angle is 90 degrees.

A 404:3dB coupler superimposes the light output by the first optical waveguide and the second optical waveguide to form a qubit.

Wherein, the qubit outputted in this step is an arbitrary qubit state, which is related to the specific structure of the modified unequal-arm Mach-Zehnder interferometer and the values of α and φ.

Illustratively, when the phase modulator is located on a transmission path formed by the first optical waveguide, the polarization rotator is located on a transmission path formed by the second optical waveguide, and the first optical waveguide and the polarization beam splitter are a vertically polarized output outlet connection, that is, the first optical waveguide transmits the polarized light in the vertical direction, and the second optical waveguide is connected to a horizontal polarization output outlet of the polarization beam splitter, that is, the second optical waveguide When transmitting polarized light in the horizontal direction, (cosα) ² represents a single photon outputted by the polarizer, and after splitting by the polarization beam splitter, the probability of appearing in the horizontal polarization output direction or along the second optical waveguide The probability of transmission; (sinα) ² represents the probability that a single photon outputted by the polarizer, which is split by the polarization beam splitter, appears in the direction of the vertical polarization output or the probability of transmission along the first optical waveguide . Correspondingly, the quantum bit output by the 3dB coupler is: cosα|F>+exp(iφ)sinα|S>, wherein α is the polarization angle of the polarized light formed by the polarizer after a single photon as described above; φ is the angle modulated by the phase modulator described above; |F> is the qubit of the pre-timing pulse state; |S> is the qubit of the post-timing pulse state.

According to the above formula, if the value of α is 0 degrees, the quantum bit output by the 3dB coupler is the quantum bit of the front timing pulse state |F>;

If the value of α is 90 degrees, the quantum bit output by the 3dB coupler is a qubit of the post-time pulse state |S>;

If the value of α is 45 degrees and the value of φ is 0 degrees, the quantum bits output by the 3dB coupler are front and rear timing pulse superposition states.

If the value of α is 45 degrees and the value of φ is 90 degrees, the quantum bits output by the 3dB coupler are front and rear timing pulse superposition states.

If the value of α is 45 degrees and the value of φ is 180 degrees, the quantum bits output by the 3dB coupler are front and rear timing pulse superposition states.

If the value of α is 45 degrees and the value of φ is 270 degrees, the quantum bits output by the 3dB coupler are front and rear timing pulse superposition states.

If the value of α is 135 degrees and the value of φ is 0 degrees, the quantum bits output by the 3dB coupler are before and after the timing pulse superposition state.

If the value of α is 135 degrees and the value of φ is 90 degrees, the quantum bits output by the 3dB coupler are front and rear timing pulse superposition states.

If the value of α is 135 degrees and the value of φ is 180 degrees, the quantum bits output by the 3dB coupler are front and rear timing pulse superposition states.

If the value of α is 135 degrees and the value of φ is 270 degrees, the quantum bits output by the 3dB coupler are front and rear timing pulse superposition states.

In other implementations of this step, when the phase modulator is located on a transmission path formed by the first optical waveguide, the polarization rotator is located on a transmission path formed by the second optical waveguide, and the first optical waveguide is connected a horizontal polarization output port of the polarization beam splitter, wherein when the second optical waveguide is connected to the vertical polarization output port of the polarization beam splitter, the quantum bit output by the 3dB coupler is sinα|F>+exp(iφ)cosα |S>.

When the phase modulator and the polarization rotator are both located on a transmission path formed by the second optical waveguide, and the first optical waveguide is connected to a vertical polarization output port of the polarization beam splitter, the second optical waveguide When the horizontal polarization output of the polarization beam splitter is connected, the quantum bit output by the 3dB coupler is: exp(iφ)cosα|F>+sinα|S>.

When the phase modulator and the polarization rotator are both located on a transmission path formed by the second optical waveguide, and the first optical waveguide is connected to a horizontal polarization output port of the polarization beam splitter, the second optical waveguide When the vertical polarization output of the polarization beam splitter is connected, the quantum bit output by the 3dB coupler is: exp(iφ)sinα|F>+cosα|S>.

For other implementations, the quantum bits output by the 3dB coupler can be obtained according to the above implementation manner provided by the embodiments of the present invention.

The method for preparing quantum bits according to an embodiment of the present invention, when preparing a qubit, a polarizer located between a single photon source and a modified unequal arm Mach-Zehnder interferometer can process a single photon emitted by a single photon source Outputting polarized light of any angle; then using a polarization beam splitter instead of the 3dB coupler in the prior art to split the polarized light output from the polarizer to obtain two polarized lights of different polarization directions; the first optical waveguide and the first optical waveguide The two optical waveguides respectively transmit polarized light of two different polarization directions, and in the process of transmission, in order to ensure that the polarized light in the two directions after the splitting can interfere at the 3 dB coupler, the polarization rotator is used to take one direction. The polarized light is polarized and rotated. In addition, the phase modulator in the improved unequal-arm Mach-Zehnder interferometer can modulate the phase of the polarized light in one direction to any angle; the last 3dB coupler superimposes the two polarized lights in the same direction. Quantum bits. Since the polarizer is capable of polarizing light emitted from a single photon source to obtain polarized light of any angle, and the phase modulator in the modified unequal arm Mach-Zehnder interferometer is capable of modulating at any angle, the present invention provides The qubit preparation device can realize the preparation of qubits of any form.

In summary, the apparatus and method for preparing quantum bits provided by the embodiments of the present invention can realize the preparation of qubits of arbitrary forms on the basis of reducing line insertion loss.

The above is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily think of changes or substitutions within the technical scope of the present invention. It should be covered by the scope of the present invention.

Claims

A device for preparing quantum bits, comprising: a single photon source, a polarizer and a modified unequal arm Mach-Zehnder interferometer, which are sequentially connected, wherein:

The improved unequal-arm Mach-Zehnder interferometer includes a polarization beam splitter, a first optical waveguide, a second optical waveguide, a 3dB coupler, and a phase modulation on a transmission path formed by the first optical waveguide or the second optical waveguide a polarization rotator on a transmission path formed by the first optical waveguide or the second optical waveguide; a length of the first optical waveguide is greater than a length of the second optical waveguide, and an input end of the polarization beam splitter The polarizer is connected, a first output end of the polarizing beam splitter is coupled to an input end of the first optical waveguide, a second output end of the polarizing beam splitter and an input of the second optical waveguide End connection, an output end of the first optical waveguide and the second optical waveguide are respectively connected to an input end of the 3dB coupler;

The polarizer is configured to process the single photon emitted by the single photon source to output polarized light having a polarization angle of α, and the value of α ranges from 0 degrees to 360 degrees;

The polarizing beam splitter is configured to split polarized light having the polarization angle α to form polarized light of two different polarization directions;

The first optical waveguide and the second optical waveguide are configured to respectively transmit the polarized light of the two different polarization directions; wherein a polarization rotator for polarizing light transmitted along an optical waveguide corresponding to the polarization rotator The polarization angle is rotated by a first predetermined angle such that the polarization angles of the polarized light output by the first optical waveguide and the second optical waveguide are the same; a phase modulator for transmitting the optical waveguide corresponding to the phase modulator The phase of the polarized light is modulated by a second predetermined angle φ, and the second preset angle φ ranges from 0 degrees to 360 degrees;

The 3dB coupler is configured to superimpose light output by the first optical waveguide and the second optical waveguide to form a qubit.
The apparatus according to claim 1, wherein said polarization beam splitter is for splitting the outgoing light from the polarizer into outgoing light of a horizontal polarization direction and a vertical polarization direction.
The apparatus according to claim 2, wherein said polarization rotator rotates the polarization of the outgoing light from the polarization beam splitter by 90 degrees.
The device of claim 1 wherein:

The apparatus also includes a controller for controlling a polarization angle α of the polarized light output by the polarizer and a value of the second predetermined angle φ modulated by the phase modulator.
The apparatus according to any one of claims 1 to 4, wherein the phase modulator is located on a transmission path formed by the first optical waveguide, and the polarization rotator is located in the second optical waveguide On the transmission path.
A method of preparing a qubit, which is characterized by being applied to the apparatus of any one of claims 1 to 5, the method comprising:

The polarizer processes the single photon emitted by the single photon source to output polarized light having a polarization angle of α, and the value of α ranges from 0 to 360 degrees;

The polarizing beam splitter splits the polarized light having the polarization angle α to form polarized light of two different polarization directions;

The first optical waveguide and the second optical waveguide respectively transmit the polarized light of the two different polarization directions, wherein during the transmission, the polarization rotator polarizes the polarized light transmitted along the optical waveguide corresponding to the polarization rotator The angle is rotated by a first predetermined angle such that the polarization angles of the polarized light output by the first optical waveguide and the second optical waveguide are the same; the phase modulator will phase the polarized light transmitted along the optical waveguide corresponding to the phase modulator Modulating a second preset angle φ, and the value of φ ranges from 0 degrees to 360 degrees;

The 3dB coupler superimposes the light output by the first optical waveguide and the second optical waveguide to form a qubit.
The method according to claim 6, wherein the polarizing beam splitter splits the polarized light having the polarization angle α to form polarized light of two different polarization directions, and specifically includes:

The polarization beam splitter splits the polarized light having the polarization angle α to form polarized light in the horizontal direction and polarized light in the vertical direction.
The method according to claim 7, wherein when said phase modulator is located on a transmission path formed by said first optical waveguide, said polarization rotator is located on a transmission path formed by said second optical waveguide, and said An optical waveguide transmits the polarized light in a vertical direction, and when the second optical waveguide transmits the polarized light in the horizontal direction, a quantum bit output by the 3dB coupler is a quantum bit of a superimposed state of the front and rear timing pulses: cosα| F>+exp(iφ)sinα|S>, where |F> is the qubit of the pre-timing pulse state; |S> is the qubit of the post-timing pulse state.