Quantum state encoding device and method without long delay line

Abstract

The present application discloses a quantum state encoding device and method without a long delay line. The device and method use a random minute radio frequency signal to modulate a laser to achieve phase difference adjustment between pulse pairs, while simultaneously employing chopping to achieve a constant phase difference between two laser pulses of a pulse pair. Thus, without the aid of a long delay line interferometer or multiple lasers used for injection locking, the requirements for phase randomization between pulse pairs and a constant or specific phase difference between the two laser pulses in each pulse pair can be simultaneously satisfied. In addition, the present application can be implemented by means of conventional lasers, intensity modulators, and phase modulators, facilitating chip integration and achieving high yield and good stability.

Description

A quantum state encoding device and method without long delay lines

[0001] This application claims priority to Chinese Patent Application No. 202411919159.3, filed on December 24, 2024, entitled "A Quantum State Encoding Device and Method Without Long Delay Lines", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of quantum information technology, specifically to a quantum state encoding device and method that does not require a long delay line, which is particularly suitable for time phase encoding and phase encoding quantum key distribution (QKD) systems. Background Technology

[0003] Quantum key distribution (QKD) systems, based on the quantum no-cloning and uncertainty principles, provide a high level of information security protection against high-computing-power attacks. As QKD technology moves from the laboratory to practical applications, small size, low cost, and high stability have become current research priorities and are also the core competitive advantages of QKD products.

[0004] Quantum state encoding devices are one of the core functional units in QKD systems. Currently, they are generally implemented by combining traditional fiber optic devices, resulting in large size and high cost. Therefore, realizing small-sized, low-cost, and highly stable quantum state encoding devices is key to reducing system size and cost.

[0005] Figure 1 illustrates a phase encoding scheme in the prior art, in which a narrow laser pulse is generated by a laser, the narrow laser pulse is used to generate a pulse pair by a fiber-optic Faraday-Michelson interferometer, and then the phase difference between the two laser pulses is formed by modulation using a phase modulator PMa. In this prior art scheme, the bias current of the laser is set below its threshold current to ensure that the laser pulses generated by the laser have random phase.

[0006] Figure 2 illustrates a prior art time-phase state encoding scheme, in which a laser generates narrow laser pulses, which are then used by an unequal-arm interferometer (AMZI) to generate pulse pairs. A phase shifter is then used to modulate the phase difference between the two laser pulses forming the pulse pair. In this prior art scheme, the laser bias current must also be set below a threshold current to ensure that the laser pulses output by the laser have random phase characteristics.

[0007] Figure 3 illustrates another time-phase state encoding scheme in the prior art, in which a pair of locked laser pulses is generated using two lasers (master and slave) and an optical circulator, simultaneously achieving phase modulation between the two pulses of the pulse pair. In this scheme, the bias current of the master laser also needs to be set below a threshold current to ensure that the phase of different laser pulse pairs is random.

[0008] In general, the QKD process usually requires a pulse pair of two optical pulses with a constant phase difference, and the phases of different pulse pairs are random. The existing technology mainly uses the following two methods to obtain the above pulse pairs.

[0009] One approach is the interferometer method: An unequal-arm interferometer is used to split an input laser pulse into two, providing a pair of laser pulses with a constant phase difference—that is, a pulse pair with a constant phase difference. Simultaneously, the laser's DC bias is set below the threshold current, and radio frequency modulation causes the laser to output narrow laser pulses to be provided to the unequal-arm interferometer. Since the laser pulses output are all generated by spontaneous emission, their phases are random, thus ensuring that the phases of the different pulse pairs formed from these different laser pulses are also random.

[0010] The second method is injection locking: the bias current of the master laser is set below the threshold current to ensure that the phase of the laser pulse modulated each time is random. The phase of the laser pulse excited by the slave laser depends on the laser phase of the master laser. After the master laser generates a wide pulse, it injects a pair of laser pulses with a constant or specific phase difference into the slave laser.

[0011] Interferometer implementations typically include schemes using discrete components and schemes using chip-based architectures. When using discrete components, controlling the arm length difference in fiber optic interferometers is complex, and the provided phase difference is easily affected by ambient temperature and vibration. When using chip-based architectures, due to the large length difference between the two arms and the susceptibility of the material's refractive index to temperature variations, the provided phase difference also suffers from the problem of being easily affected by ambient temperature, thus requiring very high temperature control precision.

[0012] When using the injection-locked method, in addition to the master and slave lasers and the optical circulator, an intensity modulator is usually required. Furthermore, the chip-based integration of lasers is generally based on InP material, which further reduces the yield of integrating multiple devices. Summary of the Invention

[0013] To address the aforementioned problems in existing technologies, this application proposes a quantum state encoding device and method. This method utilizes random, minute radio frequency signals to modulate a laser, achieving phase difference adjustment between pulse pairs. Simultaneously, chopping is employed to maintain a constant phase difference between the two laser pulses in the pulse pair. This eliminates the need for long-delay interferometers or multiple lasers for injection locking, simultaneously satisfying the requirements of phase randomization between pulse pairs and a constant or specific phase difference between the two laser pulses in a pulse pair. Furthermore, this application can be implemented using conventional lasers, intensity modulators, and phase modulators, facilitating chip integration and offering high yield and stability.

[0014] Specifically, the first aspect of this application relates to a quantum state encoding device that does not require a long delay line, which includes a laser, a driving signal module and a quantum state modulation module;

[0015] The drive signal module is configured to output a laser drive signal, which includes a superimposed DC signal portion and a radio frequency signal portion. The amplitude of the DC signal portion is greater than the threshold current of the laser, and the radio frequency signal portion includes multiple radio frequency signals with random amplitudes and / or widths.

[0016] The laser is configured to output a continuous laser signal under the drive of the laser driving signal; and,

[0017] The quantum state modulation module includes a first intensity modulation unit, which is configured to chop the continuous laser signal in response to the radio frequency signal to generate a pulse pair, wherein the two laser pulses of the pulse pair have a constant phase difference.

[0018] Furthermore, the drive signal module includes a DC signal source, an RF signal source, and a DC biaser Bias-Tee;

[0019] The DC signal source is configured to generate the DC signal portion;

[0020] The radio frequency signal source is configured to generate the radio frequency signal portion;

[0021] The DC bias unit Bias-Tee is configured to output the laser drive signal based on the DC signal portion and the radio frequency signal portion.

[0022] Furthermore, the radio frequency signal source is configured to determine the amplitude and / or width of the radio frequency signal based on random numbers.

[0023] Furthermore, the quantum state modulation module also includes a second intensity modulation unit and / or a phase modulation unit;

[0024] The second intensity modulation unit is configured to modulate the intensity of one or both of the two laser pulses in the pulse pair;

[0025] The phase modulation unit is configured to perform phase modulation on one or both of the two laser pulses of the pulse pair.

[0026] Preferably, the quantum state modulation module is implemented in the form of an optical chip. The intensity modulation unit can be implemented using a Mach-Zehnder interferometer, and the phase modulation unit can be implemented using a high-speed phase shifter; the beam splitter used in the Mach-Zehnder interferometer is a multimode interferometer; the phase shifter used in the Mach-Zehnder interferometer is based on the thin-film lithium niobate electro-optic effect or the plasma dispersion effect.

[0027] The second aspect of this application relates to a quantum state encoding method that does not require a long delay line, which includes a driving signal generation step, a continuous laser generation step, and a quantum state modulation step;

[0028] The driving signal generation step is used to generate a laser driving signal, which includes a superimposed DC signal portion and a radio frequency signal portion. The amplitude of the DC signal portion is greater than the threshold current of the laser, and the radio frequency signal portion includes multiple radio frequency signals with random amplitudes and / or widths.

[0029] The continuous laser generation step is used to drive the laser to generate a continuous laser signal using the laser driving signal; and...

[0030] In the quantum state modulation step, corresponding to the radio frequency signal, the continuous laser signal is chopped by intensity modulation to generate a pulse pair, wherein the two laser pulses of the pulse pair have a constant phase difference.

[0031] Furthermore, the amplitude and / or width of the radio frequency signal are determined based on random numbers.

[0032] Furthermore, in the quantum state modulation step, one or both of the two laser pulses of the pulse pair are also subjected to intensity modulation; and / or, one or both of the two laser pulses of the pulse pair are also subjected to phase modulation.

[0033] Preferably, the quantum state encoding method of this application can be implemented using the quantum state encoding device described above. Attached Figure Description

[0034] The specific embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0035] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 schematically illustrates a phase encoding scheme in the prior art;

[0037] Figure 2 schematically illustrates a time phase coding scheme in the prior art;

[0038] Figure 3 schematically illustrates another time phase coding scheme in the prior art;

[0039] Figure 4 schematically shows the structural framework of the quantum state encoding device without long delay lines according to this application;

[0040] Figure 5 schematically illustrates the encoding process of the quantum state encoding method according to this application. Detailed Implementation

[0041] In the following description, exemplary embodiments of this application will be described in detail with reference to the accompanying drawings. The embodiments below are provided by way of example in order to fully convey the spirit of this application to those skilled in the art. Therefore, this application is not limited to the embodiments disclosed herein.

[0042] Figure 4 shows an example of a quantum state encoding device that does not require a long delay line according to this application.

[0043] As shown in the figure, the quantum state encoding device of this application may mainly include a laser, a driving signal module, a quantum state modulation module, and a control module.

[0044] The drive signal module of this application is mainly used to provide a laser drive signal for the laser. The laser drive signal includes a superimposed DC signal part and a radio frequency signal part, which are used for DC bias and phase random modulation of the laser, respectively.

[0045] In the example of Figure 4, the drive signal module may include a DC signal source, an RF signal source, and a DC bias-Tee.

[0046] The DC signal source and the RF signal source can be connected to the DC bias port DC and the RF port RF of the DC biaser Bias-Tee, respectively, to provide DC and RF signals to the DC biaser Bias-Tee. This allows the output of a laser drive signal with superimposed DC and RF signal components at the RF-DC port RF-DC of the DC biaser Bias-Tee, which is used to drive the laser.

[0047] In this application, the DC signal provided by the DC signal source has a current greater than the laser threshold current I. th The amplitude of the laser is adjusted so that, unlike existing technologies, the DC bias applied to the laser is always above its threshold current, ensuring that the laser generates a continuous laser signal in a stimulated manner. This laser signal has less jitter and chirp, thus allowing for higher interference contrast in QKD systems and reducing system error rates.

[0048] Specifically, this application configures the radio frequency (RF) signal source to generate RF signals based on random numbers, that is, to determine the amplitude and / or width of the generated RF signal according to random numbers. In this way, by providing a random number signal to the RF signal source, the amplitude and / or width of the RF signal output by the RF signal source can be guaranteed to exhibit randomness.

[0049] In the example of Figure 4, random numbers can be generated by a random number generator and a set of random numbers can be provided to an RF signal source (e.g., an RF LD) by a control module (e.g., a controller), thereby allowing the RF signal source to generate and output a set of RF signals with random amplitude and / or width corresponding to the set of random numbers.

[0050] Therefore, the laser drive signal for the laser can include a DC signal portion and a radio frequency (RF) signal portion, wherein the DC signal portion originating from the DC signal source has an amplitude greater than the laser threshold current, while the RF signal portion originating from the RF signal source has multiple RF signals with random amplitudes and / or widths.

[0051] When, for example, a DC bias-Tee outputs a laser drive signal to a laser to drive it to generate a continuous laser signal, the laser can generate a laser signal with less jitter and chirp in a stimulated excitation manner by means of the DC current portion of the bias-Tee that has an amplitude higher than the laser's threshold current. At the same time, since different phases can be modulated on the laser signal generated by the laser by means of radio frequency signals with different amplitudes or widths in the laser drive signal, a random phase can be modulated on the continuous laser signal by means of the radio frequency signal portion of the laser drive signal that includes multiple radio frequency signals with random amplitudes and / or widths, thereby giving the continuous laser signal a certain degree of phase randomness.

[0052] Referring again to Figure 4, the quantum state modulation module may include a first intensity modulation unit, such as intensity modulator 1.

[0053] In the example of Figure 4, the first intensity modulation unit can, under the drive of the radio frequency drive signal IM1 provided by the controller, respectively correspond to multiple radio frequency signals in the radio frequency signal section to modulate the intensity of the continuous laser signal and generate a series of pulse pairs in a chopping manner, wherein each pulse pair corresponds to one radio frequency signal in the radio frequency signal section.

[0054] Since the two laser pulses of the same pulse pair are generated by chopping the continuous laser signal portion corresponding to the same radio frequency signal in the laser driving signal, there is a constant phase difference between the two laser pulses of the same pulse pair, which fulfills the requirement of pulse pairs with constant phase difference in QKD encoding.

[0055] Since different pulse pairs originate from the laser signal portions corresponding to different radio frequency signals in the laser driving signal, and the phase of the laser signal portions corresponding to different radio frequency signals in the laser driving signal is random, the phase of different pulse pairs generated by the first intensity modulation unit is also random, thus realizing the requirement for random phase between pulse pairs in QKD encoding.

[0056] Therefore, in the quantum state encoding device of this application, by means of a specific driving signal module, a laser, and a quantum state modulation module including a first intensity modulation unit, a pulse pair with a constant phase difference between two laser pulses can be obtained simply by using the chopping process of a conventional intensity modulator. At the same time, the random phase modulation of the laser signal by the random radio frequency signal in the laser driving signal is used to achieve phase difference adjustment between the pulse pairs, thereby obtaining phase randomization between the pulse pairs. This eliminates the need for the long delay line interferometer required in existing interferometer implementations, and also eliminates the need to introduce an additional phase modulator to achieve phase randomization as in existing chopping schemes. Furthermore, it eliminates the need to keep the laser DC bias below the threshold current as in existing injection-locked implementations, thus allowing for laser pulses with smaller jitter and chirp.

[0057] Referring further to Figure 4, the quantum state modulation module of this application may also include a second intensity modulation unit (e.g., intensity modulator 2) for intensity modulation of one or both of the two laser pulses of the pulse pair output by the first intensity modulation unit to achieve the desired decoy state or time-state coded modulation.

[0058] In the example of Figure 4, the second intensity modulation unit can modulate the intensity of one or both of the two laser pulses in the pulse pair under the drive of the radio frequency drive signal IM2 provided by the controller, modulating the amplitude of the pulse pair or the amplitude difference between the two laser pulses, so as to realize the decoy state and / or time state modulation required in quantum key distribution.

[0059] Those skilled in the art will understand that in a phase coding scheme, decoy state modulation can be performed using a second intensity modulation unit.

[0060] In the time-phase coding scheme, a second intensity modulation unit is needed to perform decoy state and time-state modulation.

[0061] Referring further to Figure 4, a phase modulation unit (e.g., a phase modulator) can also be set in the quantum state modulation module of this application to perform phase modulation on one or both of the two laser pulses of the pulse pair to achieve the required phase-coded modulation.

[0062] In the example of Figure 4, the phase modulation unit can perform phase modulation on one or both of the two laser pulses of the pulse pair under the drive of the radio frequency drive signal PM provided by the controller, modulating the phase difference between the two laser pulses of the pulse pair to achieve the phase modulation required in quantum key distribution.

[0063] Those skilled in the art will understand that, in a phase encoding scheme, a phase difference of 0, π / 2, π, and 3π / 2 can be modulated between two laser pulses of a pulse pair using a phase modulation unit.

[0064] In the time-phase coding scheme, the phase difference between 0 and π can be modulated between the two laser pulses of a pulse pair using a phase modulation unit.

[0065] In a preferred embodiment, the quantum state modulation module of this application can be implemented as an optical chip, for example, by integrating a first intensity modulation unit, a second intensity modulation unit, and a phase modulation unit onto the same optical chip. As an example, the quantum state modulation module can be implemented as an optical chip using SOI technology or thin-film lithium niobate technology.

[0066] When using an optical chip, the intensity modulation unit can be implemented using a Mach-Zehnder interferometer that includes a beam splitter and a high-speed phase shifter. Preferably, a multimode interferometer can be used to implement the beam splitter, and the high-speed phase shifter can be implemented based on the electro-optic effect of thin-film lithium niobate or the plasma dispersion effect of silicon materials.

[0067] When using optical chips, the phase modulation unit can be implemented using a high-speed phase shifter, such as a high-speed phase shifter implemented using the electro-optic effect of thin-film lithium niobate or the plasma dispersion effect of silicon materials.

[0068] Preferably, the laser can be connected to the quantum state modulation module via optical fiber, or integrated with the quantum state modulation module via a hybrid integration method.

[0069] To better understand the principle of the quantum state encoding device of this application, the quantum state encoding method of this application will be explained in detail below with reference to Figure 5.

[0070] The quantum state encoding method according to this application can mainly include a driving signal generation step, a continuous laser generation step, and a quantum state modulation step.

[0071] In the driving signal generation step, a laser driving signal can be generated using a driving signal module, which includes a superimposed DC signal component and a radio frequency signal component.

[0072] For example, as shown in Figure 5, the DC signal portion can have a current greater than the laser threshold current I. th The amplitude of the radio frequency signal can be further specified. The radio frequency signal portion may include multiple radio frequency signals with random amplitudes and / or widths.

[0073] In the continuous laser generation step, the laser generates a continuous laser signal under the drive of a laser driving signal. Different phases can be obtained on the laser signal corresponding to different radio frequency signals in the laser driving signal, thereby achieving a random phase distribution on the laser signal output by the laser by utilizing the randomness of the radio frequency signals.

[0074] In the quantum state modulation step, the first intensity modulation unit in the quantum state modulation module can be used to generate multiple pulse pairs by chopping the continuous laser signal in accordance with the radio frequency signal, and the two laser pulses in the same pulse pair have a constant phase difference. The phases of different pulse pairs exhibit randomness.

[0075] For example, as shown in Figure 5, the phase difference between two laser pulses in the same pulse pair Constant as Phase difference between adjacent pulse pairs (e.g.) It is modulated by the radio frequency signal (RF LD) in the laser driving signal, and exhibits randomness.

[0076] Furthermore, the quantum state modulation step of this application may also include the step of using a second intensity modulation unit in the quantum state modulation module to intensity modulate one or both of the two laser pulses of the pulse pair to allow for decoy state and / or time-state coded modulation.

[0077] For example, as shown in Figure 5, the amplitudes of the two laser pulses in a pulse pair can be modulated simultaneously to perform decoy state coding modulation; the amplitude difference between the two laser pulses in a pulse pair can also be modulated to perform time state coding modulation.

[0078] Furthermore, the quantum state modulation step of this application may also include a step of using the phase modulation unit in the quantum state modulation module to perform phase modulation on one or both of the two laser pulses of the pulse pair, so as to allow phase-coded modulation to be realized.

[0079] For example, as shown in Figure 5, a phase difference can be modulated between the two laser pulses of a pulse pair by controlling the radio frequency drive signal PM. To achieve the required phase-coded modulation.

[0080] In summary, the quantum state encoding device and method of this application achieve phase difference adjustment between pulse pairs by modulating the laser with random, minute radio frequency signals, and simultaneously achieve a constant phase difference between the two laser pulses of the pulse pair through chopping. This eliminates the need for a long-delay line interferometer, while simultaneously satisfying the requirements of phase randomization between pulse pairs and a constant or specific phase difference between the two laser pulses of the pulse pair. Furthermore, this application can be implemented using conventional lasers, intensity modulators, and phase modulators, facilitating chip integration.

[0081] More specifically, compared with the existing method of generating pulse pairs based on interferometer delay lines, this application does not require an unequal-arm interferometer, which can avoid the shortcomings of unequal-arm interferometers such as arm length difference control and susceptibility to environmental changes.

[0082] Compared to existing chopping schemes, this application achieves phase adjustment through radio frequency modulation within the laser, eliminating the need for an additional phase modulator for phase randomization. Furthermore, the phase modulation in this application is based on intracavity adjustment within the laser cavity, significantly reducing the modulation voltage required for single-pass phase adjustment compared to conventional phase modulators, thus greatly simplifying the driving circuit.

[0083] Compared to existing injection-locking schemes, this application ensures that the laser's DC bias is always above its threshold current, which can achieve less jitter and chirp, thereby allowing for higher interference contrast and a lower system error rate.

[0084] Although the present application has been described above with reference to the accompanying drawings and specific embodiments, those skilled in the art will readily recognize that the above embodiments are merely exemplary and used to illustrate the principles of the present application, and do not limit the scope of the present application. Those skilled in the art can make various combinations, modifications and equivalent substitutions to the above embodiments without departing from the spirit and scope of the present application.

Claims

1. A quantum state encoding device that does not require a long delay line, comprising a laser, a driving signal module, and a quantum state modulation module; The drive signal module is configured to output a laser drive signal, which includes a superimposed DC signal portion and a radio frequency signal portion. The amplitude of the DC signal portion is greater than the threshold current of the laser, and the radio frequency signal portion includes multiple radio frequency signals with random amplitudes and / or widths. The laser is configured to output a continuous laser signal under the drive of the laser driving signal; and, The quantum state modulation module includes a first intensity modulation unit, which is configured to chop the continuous laser signal in response to the radio frequency signal to generate a pulse pair, wherein the two laser pulses of the pulse pair have a constant phase difference.

2. The quantum state encoding device as described in claim 1, wherein, The drive signal module includes a DC signal source, an RF signal source, and a DC biaser (Bias-Tee). The DC signal source is configured to generate the DC signal portion; The radio frequency signal source is configured to generate the radio frequency signal portion; The DC bias unit Bias-Tee is configured to output the laser drive signal based on the DC signal portion and the radio frequency signal portion.

3. The quantum state encoding device as described in claim 2, wherein, The radio frequency signal source is configured to determine the amplitude and / or width of the radio frequency signal based on random numbers.

4. The quantum state encoding device as described in claim 1, wherein, The quantum state modulation module further includes a second intensity modulation unit and / or a phase modulation unit; The second intensity modulation unit is configured to modulate the intensity of one or both of the two laser pulses in the pulse pair; The phase modulation unit is configured to perform phase modulation on one or both of the two laser pulses of the pulse pair.

5. The quantum state encoding device as described in claim 4, wherein, The quantum state modulation module is implemented in the form of an optical chip.

6. The quantum state encoding device as described in claim 5, wherein, The intensity modulation unit is implemented using a Mach-Zehnder interferometer, and the phase modulation unit is implemented using a high-speed phase shifter; The beam splitter used in the Mach-Zehnder interferometer is a multimode interferometer; The phase shifter used in Mach-Zehnder interferometers is based on the electro-optic effect or the plasma dispersion effect of thin-film lithium niobate.

7. A quantum state encoding method without long delay lines, comprising a driving signal generation step, a continuous laser generation step, and a quantum state modulation step; The driving signal generation step is used to generate a laser driving signal, which includes a superimposed DC signal portion and a radio frequency signal portion. The amplitude of the DC signal portion is greater than the threshold current of the laser, and the radio frequency signal portion includes multiple radio frequency signals with random amplitudes and / or widths. The continuous laser generation step is used to drive the laser to generate a continuous laser signal using the laser driving signal; and... In the quantum state modulation step, corresponding to the radio frequency signal, the continuous laser signal is chopped by intensity modulation to generate a pulse pair, wherein the two laser pulses of the pulse pair have a constant phase difference.

8. The quantum state encoding method as described in claim 7, wherein, The amplitude and / or width of the radio frequency signal are determined based on random numbers.

9. The quantum state encoding method as described in claim 7, wherein, In the quantum state modulation step, one or both of the two laser pulses of the pulse pair are also intensity modulated; And / or, phase modulation may also be applied to one or both of the two laser pulses in the pulse pair.

10. The quantum state encoding method as described in claim 7, implemented by means of the quantum state encoding device as described in any one of claims 1-6.

Images