Sending end and method capable of weakening QKD decoy state spectral resolution

Abstract

The invention discloses a transmitting end and a method capable of weakening QKD decoy state spectral resolution, which adopt a technical concept of weakening the QKD decoy state spectral resolution by controlling modulation voltages at weak light positions among pulses, and enable the modulation voltages corresponding to different state positions to have rising edges and / or falling edges with the same slope. And the frequency shift amount and the frequency shift direction of the weak light before and after different state positions are consistent, so that the distinguishability between different state spectrums is weakened, and a spectrum side channel attack defense function such as frequency shift attack and the like can be provided in a simple and extremely low-cost manner.

Description

Technical Field

[0001] The present invention relates to the field of quantum secure communication technology, and in particular to a transmitter and method capable of weakening the spectral resolution of a QKD decoy state, which can defend against spectral side channel attacks such as frequency shift attacks. Background Art

[0002] Quantum key distribution (QKD) fundamentally differs from classical cryptographic systems in that it uses single photons or entangled photon pairs as key carriers. In principle, it provides users with unconditionally secure confidential communications, guaranteed by the fundamental principles of quantum mechanics (such as the Heisenberg uncertainty principle, measurement collapse, and the quantum no-cloning theorem). Since ideal single-photon sources are currently unavailable for practical use, decoy state methods are used to randomly modulate pulses into weakly coherent states (signal and decoy states) of varying intensities. This allows many QKD systems based on practical non-ideal single-photon sources to achieve security comparable to those based on ideal single-photon sources. After nearly a decade of development, QKD systems based on decoy state methods have begun to commercialize. However, existing security theories for decoy state methods do not fully account for various imperfect side channels. For example, the imperfections of pulses of varying intensities in the time and frequency domains make it possible for light of different intensities to be distinguishable in these side channel dimensions. Therefore, taking necessary measures in actual systems to enhance the indistinguishability of light of different intensities in the side channel space is of great significance to enhancing the actual security of QKD.

[0003] Figure 1 The basic architecture of an existing decoy-state QKD transmitter is shown. Within the transmitter, a pulsed laser PL first emits coherent light pulses with a certain repetition frequency and uniform intensity. These light pulses can be obtained by directly controlling the internal modulation of the switching current of a continuous laser, or by external modulation of the continuous laser using an intensity modulator. The light pulses are randomly modulated into a signal state and a decoy state (i.e., pulses of different intensities) by the intensity modulator IM. The intensity-modulated light pulses are then applied with encoded information by an encoder, polarization compensation by a polarization controller PC, and then attenuated to a single-photon energy level by an attenuator ATT. Finally, they are output from the transmitter's output IO into the quantum channel, reaching the receiver and being detected.

[0004] Figure 2The basic principle of preparing a decoy state with the help of an intensity modulator IM in an existing decoy state QKD transmitter is shown. When different amplitude modulation voltages are applied to the intensity modulator IM, the light transmittance of the intensity modulator IM is different. For example, when modulating two-intensity quantum states (a single decoy state QKD system with only one intensity decoy state), two amplitude modulation voltages can be selected to randomly modulate the light pulse into a signal state and a decoy state, where the corresponding modulation voltages are the signal state voltage V and V respectively. S and the entrapment voltage V D , the corresponding light pulse intensities are the signal state intensity I S and the decoy state intensity I D In order to obtain a higher pulse extinction ratio, the weak light between pulses is generally modulated into an extinction state (the corresponding modulation voltage is V E , the weak light intensity is I E ). For the (modulation voltage) signal source that generates radio frequency, since the voltage actually applied to the intensity modulator IM has a certain rising edge time (for example Figure 2 t2-t1, t6-t5) and falling edge time (e.g. Figure 2 t in ( -t3, t8-t7, generally speaking, the time of the rising edge and the falling edge are approximately equal (i.e. t2-t1=t ( -t3=t6-t5=t8-t7), then applying voltages of different amplitudes will result in different voltage rising or falling edge rates (corresponding to Figure 2 The rising or falling edge slope is different), if the light intensity between pulses is not zero (i.e. I E >0), which will eventually lead to weak light at different modulation voltage change rate positions (e.g. Figure 2 The modulation spectrum of the weak light in regions 1, 2, 3 and 4 has a different frequency shift compared to the light in other positions (or the original light), and at the same time, there is a distinguishable difference between the signal state and the decoy state pulse spectra.

[0005] Since the extinction ratio of the currently used practical weak coherent pulse light source is limited, whether it is internally modulated or externally modulated, the light intensity between pulses will always be greater than zero. Therefore, this side channel with distinguishable decoy state spectrum always exists, which will have a certain impact on the actual security of QKD.

[0006] To enhance the spatial indistinguishability of the decoyed state spectral side channel and thus strengthen the practical security of QKD, the conventional approach in this field is to increase the on-off extinction ratio of the pulsed laser (PL) and the extinction ratio of the intensity modulator (IM), thereby minimizing the inter-pulse intensity. However, due to current manufacturing processes for pulsed lasers (PL) and intensity modulators (IM), achieving an infinitely high extinction ratio is impossible. This approach merely minimizes device imperfections but does not fundamentally resolve the problem, and is also costly.

[0007] To address this issue, the applicant has proposed a random noise-based solution, which involves introducing noise light at the rising and falling edges. For example, this involves modulating the rising and falling edge voltages into noise voltages or directly injecting noise light into the rising and falling edges of the optical path, thereby masking the distinguishability of the spectrum. However, given current technology, this approach is not only extremely difficult but also extremely costly, hindering the practical application of QKD. Summary of the Invention

[0008] In response to the above-mentioned problems existing in the prior art, the present invention discloses a transmitter and method that can weaken the discriminability of QKD decoy state spectra. For the first time, the technical concept of weakening the discriminability of QKD decoy state spectra by controlling the modulation voltage at the weak light position between pulses is introduced. By ensuring that the modulation voltages corresponding to different state positions have rising edges and / or falling edges with the same slope, the frequency shift amount and frequency shift direction of the weak light before and after different state positions are consistent, thereby weakening the discriminability between different state spectra. According to the present invention, it is only necessary to set the magnitude of the weak light modulation voltage between the intensity modulator pulses, or to cascade the intensity modulators and reasonably distribute the modulation voltage of each intensity modulator at each state position and weak light position, so as to significantly weaken the discriminability of the decoy state spectra. This method of defending against spectral side channel attacks such as frequency shift attacks is simple, efficient, and low-cost, and is extremely beneficial to the practical application of decoy state QKD systems.

[0009] Specifically, the first aspect of the present invention relates to a method for weakening the spectral resolution of QKD decoy states, which is achieved by applying a modulation voltage to an intensity modulator to modulate the intensity of a pulsed light signal to achieve the state preparation;

[0010] The modulation voltages applied to the same intensity modulator and corresponding to different state positions have rising edges and / or falling edges with the same slope.

[0011] Furthermore, the intensity modulator IM can be applied i The modulation voltage V corresponding to the weak light position Ei Configured as V Ei =(V i_1 +V i_2 ) / 2,V i_1 and V i_2is applied to the intensity modulator IM i Different modulation voltages on the CMOS and corresponding to different state positions.

[0012] Furthermore, the first modulation voltage V can be applied to the intensity modulator IM1. 1_1 =V S and the second modulation voltage V 1_2 =V D To prepare the signal state and the decoy state, and the third modulation voltage V corresponding to the weak light position on the intensity modulator IM1 is E1 Configured as V E1 =(V S +V D ) / 2.

[0013] Furthermore, the preparation of the signal state, the decoy state and the vacuum state can be realized by means of two cascaded intensity modulators IM1 and IM2; and,

[0014] Configure the intensity modulator IM1 with a first modulation voltage V corresponding to the signal state and vacuum state positions 1_1 =V S , the second modulation voltage V corresponding to the decoy state position 1_2 =V D , and the third modulation voltage V corresponding to the weak light position E1 =(V S +V D ) / 2;

[0015] The intensity modulator IM2 is configured with a first modulation voltage V corresponding to the signal state and the decoy state position. 2_1 =V S , the second modulation voltage V corresponding to the vacuum state position 2_2 =V V , and the modulation voltage V corresponding to the weak light position E2 =(V S +V V ) / 2.

[0016] Preferably, the pulsed light signal has an extinction ratio of not less than 40 dB.

[0017] The second aspect of the present invention relates to a transmitter capable of weakening the spectral resolution of the QKD decoy state, which comprises a light source, N intensity modulators IM i and control unit, N is 1 or other natural number;

[0018] The light source is configured to generate a pulsed light signal;

[0019] The intensity modulator is configured to perform intensity modulation on the pulsed light signal based on a modulation voltage to achieve the preparation of the state;

[0020] The control unit is configured to enable the modulation voltages applied to the same intensity modulator and corresponding to different state positions to have rising edges and / or falling edges with the same slope.

[0021] Furthermore, the control unit is configured to provide a signal to the intensity modulator IM corresponding to the weak light position. i Apply modulation voltage V Ei =(V i_1 +V i_2 ) / 2,V i_1 and V i_2 is applied to the intensity modulator IM i Different modulation voltages on the CMOS and corresponding to different state positions.

[0022] Furthermore, N is set to 1, and the control unit is configured to apply a first modulation voltage V to the intensity modulator IM1 respectively. 1_1 =V S and the second modulation voltage V 1_2 =V D To prepare the signal state and the decoy state, and apply a third modulation voltage V to the intensity modulator IM1 corresponding to the weak light position E1 =(V S +V D ) / 2.

[0023] Furthermore, N=2 intensity modulators IM1 and IM2 are arranged in cascade, and the control unit is configured to:

[0024] A first modulation voltage V is applied to the intensity modulator IM1 corresponding to the signal state and the vacuum state. 1_1 =V S , a second modulation voltage V is applied to the intensity modulator IM1 corresponding to the decoy state position. 1_2 =V D , and applying a third modulation voltage V to the intensity modulator IM1 corresponding to the weak light position E1 =(V S +V D ) / 2; and,

[0025] A first modulation voltage V is applied to the intensity modulator IM2 corresponding to the signal state and the decoy state. 2_1 =V S , a second modulation voltage V is applied to the intensity modulator IM2 corresponding to the vacuum state position 2_2 =V V , and applying a third modulation voltage V to the intensity modulator IM2 corresponding to the weak light position E2 =(V S +V V ) / 2.

[0026] Preferably, the light source has an extinction ratio of not less than 40 dB. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 A basic architecture of an existing decoy-state QKD transmitter is shown;

[0030] Figure 2 The basic principle of preparing the decoy state by using the intensity modulator in the existing decoy state QKD transmitter is shown;

[0031] Figure 3 An example of preparing a single decoy state by means of an intensity modulator in a decoy state QKD transmitter according to the present invention is shown;

[0032] Figure 4 An example of preparing three decoy states by means of an intensity modulator in a decoy state QKD transmitter according to the present invention is shown. DETAILED DESCRIPTION

[0033] Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided by way of example in order to fully convey the spirit of the present invention to those skilled in the art to which the present invention belongs. Therefore, the present invention is not limited to the embodiments disclosed herein.

[0034] See also Figure 1 According to the present invention, the transmitting end capable of weakening the spectral resolution of the QKD decoy state may include a light source, an intensity modulator and a control unit in terms of hardware composition.

[0035] The light source is used to generate a pulsed light signal, which can be achieved, for example, by a pulsed laser PL. In the present invention, the pulsed light signal can be obtained by directly controlling the internal modulation of the switching current of a continuous laser, or by external modulation of the continuous laser with an external intensity modulator.

[0036] In a preferred example, the light source may be configured to have an extinction ratio of not less than 40 dB, that is, the extinction ratio of the pulse light signal outputted by the light source is not less than 40 dB.

[0037] In the present invention, the intensity modulator is also used to perform different intensity modulations on the passing pulsed light signal based on the modulation voltage applied thereto, thereby realizing the preparation of the decoy state.

[0038] The number N of intensity modulators may be one or more, which is determined according to the specific decoy state scheme adopted by the transmitting end.

[0039] In the case of a single decoy state scheme (such as Figure 3 In a QKD system (shown in FIG), only a single intensity modulator may be provided, that is, N = 1. By means of the intensity modulator, two different intensity modulations are provided on the pulsed light signal, thereby enabling the preparation of the signal state and the decoy state.

[0040] In a QKD system using a multi-decoy state scheme, multiple intensity modulators can be set according to the number of decoy states to be prepared. For example, in a three-decoy state (such as Figure 4 In a QKD system (as shown), N=2 intensity modulators can be set up and the required signal state, decoy state and vacuum state can be prepared by cascade modulation of two intensity modulators.

[0041] The control unit can control the modulation voltage applied to the intensity modulator, control the intensity modulation of the pulse light signal, and thus control the preparation of various states.

[0042] Based on the above hardware configuration, the present invention innovatively proposes a method to weaken the spectral resolution of QKD decoy states based on inter-pulse weak light position modulation voltage control, which can be implemented with the help of the above control unit.

[0043] Specifically, for the electro-optical IM of the Mach Zehnder interferometer (MZI) structure commonly used in QKD systems, its principle is to split the input light into two equal beams at the entrance of the MZ interferometer. The two beams of light pass through the lithium niobate waveguides in the two arms respectively, and are coupled together at the end of the MZ interferometer and interfere with the output.

[0044] When voltage is applied to the two arms of the waveguide, the phase of the light field in the two arms will change, causing a phase difference between the two arms. Applying different voltage differences to the two arms will result in different phase differences, and ultimately different interference light intensities. The final output light field can be expressed as:

[0045]

[0046] in: is the phase difference between the two arms’ light fields; is the phase of the output light field; E0 is the input light field intensity; ω0 is the input light field frequency; γ1 and γ2 are the voltage-phase conversion coefficients of the two-arm waveguide, generally γ1 = -γ2; and are the initial phases of the light fields in the two arms respectively; V(t) is the modulation voltage applied to the interferometer (i.e., intensity modulator IM).

[0047] From the above output light field formula, it can be seen that when the modulation voltage V(t) = C (constant), the corresponding Figure 2 In the constant voltage sections t2-t3 and t6-t7, and If all are constants, the output light field is still a light field of a certain intensity with a frequency of ω0. When V(t)=V0+kt, then the corresponding Figure 2 In the rising and falling edge voltage segments, assuming but and is no longer a constant, and the final output light field can be further expressed as:

[0048]

[0049] It can be seen that the frequency of the output light field is no longer ω0, but a frequency shift occurs, and the frequency shift amount is ±ω m =±γ1k.

[0050] In the design and implementation of existing decoy-state QKD systems, researchers typically focus only on the effect of the modulation voltage at the weak light position between pulses on the maximum extinction ratio. This results in uncontrolled k-values ​​(i.e., the slopes of the voltage rising and falling edges) when preparing different quantum states, ultimately leading to a certain degree of resolution between the spectra of the signal and decoy-state pulses. Unlike conventional thinking in the prior art, the inventors have creatively proposed a new approach to reduce the resolution of the QKD decoy-state spectrum by controlling the modulation voltage at the weak light position between pulses.

[0051] Based on the above-mentioned solution proposed by the present invention, the modulation voltage applied to the intensity modulator can be controlled by means of, for example, a control unit, so that the modulation voltage applied to the same intensity modulator corresponding to different state positions has a rising edge and / or falling edge with the same slope (i.e., |k|), so that the frequency shift amount and frequency shift direction of the weak light before and after the (decoy) state prepared at these positions are consistent, thereby weakening the distinguishability between different state spectra.

[0052] Specifically, in the decoy state QKD system of the present invention, each intensity modulator IM i Configure two modulation voltages, namely the first modulation voltage V i_1 and the second modulation voltage V i_2 , so as to be applied to the intensity modulator IM at the corresponding state position under the control of, for example, a control unit. iOn this basis, a preset intensity modulation is provided to the pulse light signal to prepare the required decoy state. On this basis, a weak light position is also specifically applied to the intensity modulator IM i The modulation voltage on the Ei =(V i_1 +V i_2 ) / 2 to ensure that the frequency shift amount and frequency shift direction of the weak light before and after any state prepared by means of the intensity modulator are consistent, thereby effectively weakening the distinguishability between spectra of different states.

[0053] In order to better understand the working principle of the present invention, the following will be combined with Figure 3 and 4 The examples of the transmitting end and method of the present invention in different decoy state schemes are specifically described.

[0054] Figure 3 An example of the application of the transmitting end and method of the present invention in a single-decoy state QKD system is shown.

[0055] In a single decoy state QKD system, a single intensity modulator IM1 can usually be set to achieve the preparation of the required decoy state.

[0056] According to the present invention, the intensity modulator IM1 can be configured with a first modulation voltage V 1_1 =V S and the second modulation voltage V 1_2 =V D , so as to apply to the intensity modulator IM1 at the signal state and decoy state positions respectively under the control of, for example, a control unit, and perform intensity modulation on the pulse light signal, thereby preparing the corresponding signal state and decoy state.

[0057] According to the present invention, based on the above modulation voltage configuration, a third modulation voltage V is further configured. E1 =(V S +V D ) / 2, which is applied to the intensity modulator IM1 corresponding to the weak light position, so that the changing rate of the rising and falling edge voltages of the signal state and the decoy state pulses are kept at the same value, ensuring the consistency of the frequency shift amount and frequency shift direction of the weak light before and after the signal state and the decoy state, thereby weakening the spectral distinguishability of the signal state and the decoy state. For example, Figure 3 As shown.

[0058] Figure 4 An example of the application of the transmitting end and method of the present invention in a three-decoy state QKD system is shown.

[0059] In a three-decoy-state QKD system, two intensity modulators IM1 and IM2 can be set in a cascade manner to achieve the preparation of three states, namely, signal state, decoy state and vacuum state, by means of cascade modulation of the two intensity modulators.

[0060] According to the present invention, a first modulation voltage V can be configured for one of the intensity modulators IM1. 1_1 =V S and the second modulation voltage V 1_2 =V D , wherein (for example, under the control of a control unit): the first modulation voltage V 1_1 =V S Corresponding to the signal state and vacuum state positions, the second modulation voltage V is applied to the intensity modulator IM1. 1_2 =V D The corresponding voltage V is applied to the intensity modulator IM1 at the decoy state position. At the same time, the first modulation voltage V can also be configured for another intensity modulator IM2. 2_1 =V S and the second modulation voltage V 2_2 =V V , where: the first modulation voltage V 2_1 =V S Corresponding to the signal state and the decoy state, the second modulation voltage V is applied to the intensity modulator IM2. 1_2 =V V The corresponding voltage is applied to the intensity modulator IM2 at the vacuum state position. Thus, the signal state, vacuum state and decoy state can be prepared by means of the two intensity modulators IM1 and IM2.

[0061] According to the present invention, based on the above modulation voltage configuration, a third modulation voltage V can be configured for the intensity modulator IM1. E1 =(V S +V D ) / 2, applied to it at a weak light position; at the same time, a third modulation voltage V is configured for the intensity modulator IM2 E2 =(V S +V V ) / 2, and is also applied to the weak light position. In this way, the rate of change of the rising and falling edge voltages of each state before and after the modulation pulse of each intensity modulator can be kept the same, so that the frequency shift amount and frequency shift direction of the weak light before and after each state are consistent, thereby weakening the distinguishability of the signal state, decoy state and vacuum state spectra, for example Figure 4 As shown.

[0062] Based on the above description, it can be seen that the present invention proposes for the first time a technical concept for weakening the discriminability of QKD decoy state spectra by controlling the modulation voltage at the weak light position between pulses. By making the modulation voltages corresponding to different state positions have rising edges and / or falling edges with the same slope, the frequency shift amount and frequency shift direction of the weak light before and after different state positions are ensured to be consistent, thereby weakening the discriminability between different state spectra. According to the present invention, it is only necessary to set the magnitude of the weak light modulation voltage between the intensity modulator pulses, or to cascade the intensity modulators and reasonably distribute the modulation voltage of each intensity modulator at each state position and weak light position, so as to significantly weaken the discriminability of the decoy state spectra. This method is simple, efficient, and low-cost (even almost cost-free), which is extremely beneficial to the practical application of decoy state QKD systems.

[0063] Although the present invention has been described above through specific embodiments in conjunction with the accompanying drawings, it is easy for those skilled in the art to recognize that the above embodiments are merely exemplary and are used to illustrate the principles of the present invention. They do not limit the scope of the present invention. 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 invention.

Claims

1. A method for weakening the spectral resolution of QKD decoy states, wherein the states are prepared by applying a modulation voltage to an intensity modulator to modulate the intensity of a pulsed light signal; in, The modulation voltages applied to the same intensity modulator and corresponding to different state positions have rising edges and / or falling edges with the same slope.

2. The method according to claim 1, wherein Apply to the intensity modulator IM i The modulation voltage V corresponding to the weak light position Ei Configured as V Ei =(V i_1 +V i_2 ) / 2,V i_1 and V i_2 is applied to the intensity modulator IM i Different modulation voltages on the CMOS and corresponding to different state positions.

3. The method according to claim 1 or 2, wherein By applying a first modulation voltage V to the intensity modulator IM1, 1_1 =V S and the second modulation voltage V 1_2 =V D To prepare the signal state and the decoy state, and the third modulation voltage V corresponding to the weak light position on the intensity modulator IM1 is E1 Configured as V E1 =(V S +V D ) / 2.

4. The method according to claim 1 or 2, wherein The signal state, the decoy state and the vacuum state are prepared by means of two cascaded intensity modulators IM1 and IM2; and Configure the intensity modulator IM1 with a first modulation voltage V corresponding to the signal state and vacuum state positions 1_1 =V S , the second modulation voltage V corresponding to the decoy state position 1_2 =V D , and the third modulation voltage V corresponding to the weak light position E1 =(V S +V D ) / 2; The intensity modulator IM2 is configured with a first modulation voltage V corresponding to the signal state and the decoy state position. 2_1 =V S , the second modulation voltage V corresponding to the vacuum state position 2_2 =V V , and the modulation voltage V corresponding to the weak light position E2 =(V S +V V ) / 2.

5. The method according to claim 1, wherein The pulsed light signal has an extinction ratio of not less than 40 dB.

6. A transmitter capable of weakening the spectral resolution of a QKD decoy state, comprising a light source, N intensity modulators IM i and control unit, N is 1 or other natural number; The light source is configured to generate a pulsed light signal; The intensity modulator is configured to perform intensity modulation on the pulsed light signal based on a modulation voltage to achieve the preparation of the state; The control unit is configured to enable the modulation voltages applied to the same intensity modulator and corresponding to different state positions to have rising edges and / or falling edges with the same slope.

7. The transmitting end according to claim 6, wherein: The control unit is configured to provide the intensity modulator IM with a signal corresponding to the weak light position. i Apply modulation voltage V Ei =(V i_1 +V i_2 ) / 2,V i_1 and V i_2 is applied to the intensity modulator IM i Different modulation voltages on the CMOS and corresponding to different state positions.

8. The transmitting end according to claim 6 or 7, wherein: N is 1, and the control unit is configured to apply a first modulation voltage V to the intensity modulator IM1 respectively. 1_1 =V S and the second modulation voltage V 1_2 =V D To prepare the signal state and the decoy state, and apply a third modulation voltage V to the intensity modulator IM1 corresponding to the weak light position E1 =(V S +V D ) / 2.

9. The transmitting end according to claim 6 or 7, wherein: N=2 intensity modulators IM1 and IM2 are arranged in cascade, and the control unit is configured to: A first modulation voltage V is applied to the intensity modulator IM1 corresponding to the signal state and the vacuum state. 1_1 =V S , a second modulation voltage V is applied to the intensity modulator IM1 corresponding to the decoy state position. 1_2 =V D , and applying a third modulation voltage V to the intensity modulator IM1 corresponding to the weak light position E1 =(V S +V D ) / 2; and, A first modulation voltage V is applied to the intensity modulator IM2 corresponding to the signal state and the decoy state. 2_1 =V S , a second modulation voltage V is applied to the intensity modulator IM2 corresponding to the vacuum state position 2_2 =V V , and applying a third modulation voltage V to the intensity modulator IM2 corresponding to the weak light position E2 =(V S +V V ) / 2.

10. The transmitting end according to claim 6, wherein: The light source has an extinction ratio of not less than 40 dB.

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