WO2012018246A1

WO2012018246A1 - A six quantum state producing encoder system and a method of producing thereof

Info

Publication number: WO2012018246A1
Application number: PCT/MY2010/000293
Authority: WO
Inventors: Muhammad Syargawi Abdullah; Gunawan Witjaksono; Mohd Hadri Hafiz Mokhtar
Original assignee: Mimos Berhad
Priority date: 2010-08-05
Filing date: 2010-11-25
Publication date: 2012-02-09
Also published as: MY149261A

Abstract

A six quantum state producing encoder system (100) for deterministic six states protocol of Quantum Key Distribution is provided, the system (100) includes at least three laser diodes (610, 620, 630), at least three current drivers (510, 520, 530) wherein each of the at least three laser diodes (610, 620, 630) are at different polarization states and each laser diode is drivable by each current driver, at least three switches (410, 420, 430) connectable to the at least three current drivers (510, 520, 530), at least one pulse width modulator (PWM) generator (220) connectable to the at least three switches (410, 420, 430) and a controller wherein the at least three switches (410, 420, 430) are triggerable by the controller, wherein the system (100) is configurable to select a pair of different laser diodes with new polarization states for every two consecutive period, wherein two different laser diodes are interchangeably triggered for every two consecutive periods for automatic production of six quantum states.

Description

A SIX QUANTUM STATE PRODUCING ENCODER SYSTEM AND A METHOD OF

PRODUCING THEREOF

FIELD OF INVENTION

The present invention relates to a six quantum state producing encoder system for deterministic six states protocol of Quantum Key Distribution and a method of producing thereof. BACKGROUND OF INVENTION

Deterministic six states quantum key distribution scheme (6DP QKD) scheme relies on implementation based on biphotons (pairs of photon) source. However, to generate these biphotons source, we need a complex and expensive laser system, generally a titanium-sapphire solid state laser pumped by a diode-pumped solid state laser or by a cluttering and greedy argon-ion laser. This biphoton generation process, which is called spontaneous parametric downconversion (SPDC), is not easy to control and use, often needs high qualification maintenance like passive optical realignment, adjustment and tuning, slower driving frequency and limited to experimental scale of implementation only. Further, the process is very inefficient as it typically takes some 10¹⁰ pump photons to create one pair in a given mode.

There are a few prior arts that discuss methods of generating biphotons for 6DP QKD, however the prior arts did not provide any practical solution and still have some drawbacks. WO 2009/157756 A2 fully utilizes passive optical devices and SPDC technique to produce two correlated photons from single argon-ion laser diode and to change its polarization accordingly. However, alignment and tuning of these passive optical devices need to be done manually in order to generate sets of biphoton. Therefore, this solution is impractical, much slower, and limited to lab scale implementation only. WO 2009/157753 A2 also uses the SPDC process to generate biphotons and some electro-optical devices to manipulate its polarization. Unfortunately, control mechanism taught in this document is done outside of a laser source package. A drawback of the system is that the mechanism to produce the polarization of the biphoton is done after the laser source emits the photon. Consequently, this makes the implementation for QKD system becomes impractical as the different voltages for different polarisation transformations need to be applied accordingly. Hence, the solution slows down the system.

Thus, there is a need to provide for a cost efficient simple solution to generate biphotons naturally for better QKD implementation.

SUMMARY OF INVENTION

Accordingly there is provided a six quantum state producing encoder system for deterministic six states protocol of Quantum Key Distribution, the system includes at least three laser diodes, at least three current drivers wherein each of the at least three laser diodes are at different polarization states and each laser diode is drivable by each current driver, at least three switches connectable to the at least three current drivers, at least one pulse width modulator (PWM) generator connectable to the at least three switches and a controller wherein the at least three switches are triggerable by the controller, wherein the system is configurable to select a pair of different laser diodes with new polarization states for every two consecutive period, wherein two different laser diodes are interchangeably triggered for every two consecutive periods for automatic production of six quantum states. There is further provided a method of automatically producing six quantum states for deterministic six states protocol of Quantum Key Distribution, the method includes pulsing a plurality of signals independently in a periodic manner for a predetermined period, synchronizing between a pulse signal and a trigger signal in manipulating a plurality of laser diodes, such that at least one laser diode is activated during each period, driving the plurality of laser diodes with a modulation source and polarizing photons from actively driven laser diodes, wherein the trigger signal is configured to select a pair of different laser diodes with new polarization states for every two consecutive period, wherein two different laser diodes are interchangeably triggered for every two consecutive periods.

The present invention consists of several novel features and a combination of parts hereinafter fully described and illustrated in the accompanying description and drawings, it being understood that various changes in the details may be made without departing from the scope of the invention or sacrificing any of the advantages of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, wherein:

Figure 1 illustrates a block diagram showing the architecture of an embodiment of a six quantum state producing encoder system in the present invention;

Figure 2 illustrates a complete block diagram showing the architecture of an embodiment of a six quantum state producing encoder system in the present invention; Figure 3 illustrates a flow chart showing a method of producing deterministic six states protocol in the embodiment of the present invention; and

Figure 4 illustrates a timing chart demonstrating operation of the system and method in the embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention relates to a six quantum state producing encoder system for deterministic six states protocol of Quantum Key Distribution and a method of producing thereof. Hereinafter, this specification will describe the present invention according to the preferred embodiment of the present invention. However, it is to be understood that limiting the description to the preferred embodiment of the invention is merely to facilitate discussion of the present invention and it is envisioned that those skilled in the art may devise various modifications and equivalents without departing from the scope of the appended claims.

The following detailed description of the preferred embodiment will now be described in accordance with the attached drawings, either individually or in combination. The embodiment of the present invention provides for a six quantum state producing encoder system (100) for deterministic six states protocol of Quantum Key Distribution (QKD). Figure 1 depicts a general block diagram of the system (100).

Figure 2 shows a complete block diagram of the system (100). The system (100) includes at least three laser diodes (610, 620, 630), at least three current drivers (510, 520, 530) wherein each of the at least three laser diodes (610, 620, 630) are at different polarization states and each laser diode is drivable by each current driver. At least three switches (410, 420, 430) is connectable to the at least three current drivers (510, 520, 530).

Further, at least one pulse width modulator (PWM) generator (220) is connectable to the at least three switches (410, 420, 430) and a controller wherein the at least three switches (410, 420, 430) are triggerable by the controller. The system (100) is configurable to select a pair of different laser diodes with new polarization states for every two consecutive period, wherein two different laser diodes are interchangeably triggered for every two consecutive periods for automatic production of six quantum states. An example of the controller includes an embedded controller (200).

A clock generator (210) is further connectable to the embedded controller (200) to provide a reference clock. As shown in Figure 2, the present invention describes an encoder system 100 to produce six quantum states from three laser diodes (610, 620, 630) to produce a stream of biphotons for QKD. The embedded controller (200) and the clock generator (210) are central to the system (100). The clock generator (210) provides a reference clock signal to be used by a Random Sequence Generator (300) and a PWM Generator (220) as an input trigger.

Once clock signals are received, the Random Sequence Generator (300) and the PWM Generator (220) generate respective outputs simultaneously. A reference pulse signal coming from the PWM Generator (220) passes through the Pulse Width Controller (221 ) in order to reshape the reference pulse signal to become a narrow-width pulse signal. This attuned pulse signal is then distributed to three switches (410, 420, 430). Meanwhile, upon receiving the clock signal, the Random Sequence Generator (300) will produce a random sequence which will be used in determining which of the at least three laser diodes (610, 620, 630) is going to be triggered. The embedded controller (200) will trigger the at least three switches (410, 420, 430) by producing a trigger signal alternately, based on the random number sequence. The output of the at least three switches (410, 420, 430) provides a control signal for the at least three current drivers (510, 520, 530) and hence drive the at least three laser diodes (610, 620, 630) with modulation sources respectively. A plurality of polarization control optics (710, 720, 730) are used to prepare polarization states of coherence photons coming from actively driven laser diodes.

A method of automatically producing six quantum states for deterministic six states protocol of Quantum Key Distribution is described as seen in Figure 3. The method includes the steps of pulsing a plurality of signals independently in a periodic manner for a predetermined period, synchronizing between a pulse signal and a trigger signal in manipulating a plurality of laser diodes, such that at least one laser diode is activated during each period, driving the plurality of laser diodes with a modulation source and polarizing photons from actively driven laser diodes, wherein the trigger signal is configured to select a pair of different laser diodes with new polarization states for every two consecutive period, wherein two different laser diodes are interchangeably triggered for every two consecutive periods.

As seen above, the method starts with the step of pulsing of at least three laser diodes (610, 620, 630) independently and periodically (1 1 ). This step will continuously and periodically provide a driving modulation source for each of the laser diodes. The next step is to synchronize between a pulsing and triggering signal with a clock signal (12). This step is to ensure that only one laser diode is activated at each period. The final step is controlling the trigger signal based on input from Random Sequence Generator (13). This step is meant for selecting a pair of the laser diode with different polarization states, for every two consecutive period. The method is repeated (14) making the method automated and ideal for practical implementation. A timing chart is shown in Figure 4 that demonstrates operation of the system (100) and method. For each period (20), there is a plurality of pulse signals (21 , 24, 27) present at the at least three switches (410, 420, 430). The plurality of pulse signals is then converted to modulation voltages (23, 26, 29) by the at least three switches (410, 420, 430) whenever a plurality of trigger signals (22, 25, 28) appear during a same period. The modulation voltages (23, 26, 29) are converted to modulation sources accordingly, which in turn is used to trigger respective laser diodes, producing optical pulse signal (30). One pair of the optical signal represents one quantum state and there are six possible combinations that are produced periodically.

Unconditional security of any polarization encoding QKD protocol relies on the implementation based on a truly single photon source. Most of the QKD implementations rely on short laser pulses due to adversity in realizing single photon on-demand sources. This alternative short laser pulse is only an approximation of single photon pulses in which the photon number distribution obeys Poisson statistic. In order to achieve security in QKD, the short laser pulses scheme needs to be attenuated in such way that its average number of photon per pulse is less than 1 . Therefore, the invention as described above is able to produce six possible pairs of photons with different polarization states from different bases. Synchronization is performed between a pulse signal and a trigger signal to manipulate laser diodes in such a way to generate biphotons automatically. Control of the system is done electronically so that throughput of the system is faster and more practical for implementation. Therefore, the invention is suitable for use in applications such as, but not restricted to, quantum communication technology such as quantum cryptography, mostly in the form of Quantum Key Distribution (QKD) to offer an unconditionally secure way to establish a confidential key between distant partners through proper usage of the laws of quantum mechanics.

Claims

1. A six quantum state producing encoder system (100) for deterministic six states protocol of Quantum Key Distribution, the system (100) includes:

at least three laser diodes (610, 620, 630);

at least three current drivers (510, 520, 530) wherein each of the at least three laser diodes (610, 620, 630) are at different polarization states and each laser diode is drivable by each current driver;

at least three switches (410, 420, 430) connectable to the at least three current drivers (510, 520, 530);

at least one pulse width modulator (PWM) generator (220) connectable to the at least three switches (410, 420, 430); and

a controller wherein the at least three switches (410, 420, 430) are triggerable by the controller,

wherein the system (100) is configurable to select a pair of different laser diodes with new polarization states for every two consecutive period, wherein two different laser diodes are interchangeably triggered for every two consecutive periods for automatic production of six quantum states.

The system (100) as claimed in claim 1 , wherein the controller is an embedded controller (200).

The system (100) as claimed in claim 1 , wherein a pulse width controller (221 ) is further connectable between the at least three switches (410, 420, 430) and the at least one PWM generator (220).

4. The system (100) as claimed in claim 2, wherein a clock generator (210) is further connectable to the embedded controller (200) to provide a reference clock.

The system (100) as claimed in claim 4, wherein the reference clock signal is used by a Random Sequence Generator (300) and a PW Generator (220) as an input trigger.

The system as claimed in claim 5, wherein a reference pulse signal coming from the PWM Generator (220) passes through a Pulse Width Controller (221 ).

7. The system as claimed in claim 5, wherein the Random Sequence Generator (300) produces a random sequence which is used in determining which of the at least three laser diodes (610, 620, 630) is to be triggered.

8. The system (100) as claimed in claim 7, the embedded controller (200) triggers the at least three switches (410, 420, 430) by producing a trigger signal alternately, based on the random number sequence.

9. A method of automatically producing six quantum states for deterministic six states protocol of Quantum Key Distribution, the method includes:

i. pulsing a plurality of signals independently in a periodic manner for a predetermined period;

ii. synchronizing between a pulse signal and a trigger signal in manipulating a plurality of laser diodes, such that at least one laser diode is activated during each period;

iii. driving the plurality of laser diodes with a modulation source; and iv. polarizing photons from actively driven laser diodes,

wherein the trigger signal is configured to select a pair of different laser diodes with new polarization states for every two consecutive period, wherein two different laser diodes are interchangeably triggered for every two consecutive periods.

10. The method as claimed in claim 9, wherein the trigger signal is sourced from a clock signal.

1 1 . The method as claimed in claim 9, wherein the pulse signal is sourced from a Random Sequence Generator (300).

12. The method as claimed in claim 9, wherein the step of pulsing a plurality of signals independently and periodically (1 1 ) provides a driving modulation source for each of the laser diodes.

13. The method as claimed in claim 9, wherein the plurality of laser diodes are at least three laser diodes (610, 620, 630).

14. The method as claimed in claim 9, wherein the plurality of pulse signals is converted to modulation voltages (23, 26, 29) by at least three switches (410, 420, 430) whenever a plurality of trigger signals (22, 25, 28) appear during a same period.

15. The method as claimed in claim 14, wherein the modulation voltages (23, 26, 29) are converted to modulation sources that are used to trigger respective laser diodes and producing optical pulse signal (30).

16. The method as claimed in claim 9, wherein the method is repeated to provide automated production of six quantum states.