Continuous-variable quantum key distribution anti-noise method and system based on frequency switching

Abstract

The application provides a frequency switching-based continuous variable quantum key distribution anti-noise method and system, which comprises the following steps: a frequency switching step: acquiring a channel state, calculating a channel noise power spectrum, and finding a position with the lowest channel noise power, which is recorded as a window; and moving a transmission signal spectrum of a sending end to the window for transmission; an optimal filtering step: moving a received signal spectrum of a receiving end back to a baseband, and then filtering the received signal by using a low-pass filter to retain the transmission signal. The application combines the frequency switching idea with the filter, avoids the transmission signal from being submerged by the channel noise, is beneficial to reducing the noise components received by the receiving end of the continuous variable quantum key distribution system as much as possible, can effectively reduce the excessive noise in the system, and improves the system key rate.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of quantum secure communication, in particular to a continuous variable quantum key distribution anti-noise method and system based on frequency switching. BACKGROUND

[0002] Since human beings entered the information age, information security has been an important issue. How to protect encrypted information from being obtained or deciphered by eavesdroppers is the key to solving the problem of information security, and quantum secure communication is considered to be one of the important means to ensure information security. In quantum secure communication, the most important part is quantum key distribution. Quantum key distribution has very high security, which uses quantum characteristics such as the uncertainty principle and the non-cloning principle to ensure that quantum signals cannot be obtained by eavesdroppers, so that the security key obtained by distribution is used to encrypt the plaintext in the subsequent steps.

[0003] Continuous variable quantum key distribution is an important type of quantum variable key distribution. The most classic key distribution protocol is the GG02 protocol proposed in 2002, which uses coherent states as quantum signals carrying information, and the receiving end uses coherent detection to receive signals. Coherent state signals can be obtained by combining common lasers with optical attenuators, which is easier to implement than discrete variable quantum key distribution based on single photons, and is easier to integrate into a classical optical communication system, and has been proven to be theoretically secure, so it is a promising quantum key distribution technology.

[0004] Because coherent state signals are used to transmit information, the transmission signal power in the continuous variable quantum key distribution system is low, and the signal-to-noise ratio is lower than that of the classical optical communication system. For continuous variable quantum key distribution systems using optical fibers as quantum channels, external interference can easily be introduced into the system in the form of random noise. In particular, with the development of quantum networks, there is already a technology that densely wavelength-division multiplexes the quantum channel of continuous variable quantum key distribution with the classical communication channel. In such an information transmission process, quantum signals are easily subject to random interference from other signals, especially in the face of high-power classical signals, quantum signals are easily overwhelmed, affecting the reception of quantum signals by the receiving end. Therefore, a method is needed to resist large-power random noise for continuous variable quantum key distribution systems to ensure that the receiving end can receive quantum signals and maintain good key distribution performance. SUMMARY

[0005] In view of the defects in the prior art, the purpose of the present application is to provide a continuous variable quantum key distribution anti-noise method and system based on frequency switching.

[0006] According to the continuous variable quantum key distribution anti-noise method based on frequency switching provided by the present application, the method comprises the steps of:

[0007] frequency switching step: obtaining channel state, calculating channel noise power spectrum and finding the position of the lowest channel noise power, denoted as window, moving the transmission signal spectrum of the sending end to the window for transmission;

[0008] optimal filtering step: moving the received signal spectrum back to baseband, and then filtering the received signal using a low-pass filter to retain the transmission signal.

[0009] Preferably, the frequency switching step comprises:

[0010] Step A1: the receiving end obtains channel state;

[0011] Step A2: the receiving end calculates channel noise power spectrum, finds the local minimum value therein, denoted as window, and feeds back the window information to the sending end;

[0012] Step A3: the sending end moves the spectrum of the transmission signal according to the received window information, and moves to the window position.

[0013] Preferably, the optimal filtering step comprises:

[0014] Step B1: after receiving the signal from the sending end, the receiving end moves the signal spectrum back to baseband together with the received noise;

[0015] Step B2: the signal moved back to baseband is filtered through a low-pass filter to filter out the noise outside the passband and retain the transmission signal in the passband.

[0016] Preferably, the amplitude characteristic of the low-pass filter is:

[0017]

[0018] wherein |H(jω)| is the amplitude characteristic of the low-pass filter, ω is frequency, ω c is 3dB cutoff frequency, and N is the order of the low-pass filter.

[0019] Preferably, the low-pass filter is a Butterworth low-pass filter.

[0020] According to the present application, a frequency switching-based continuous variable quantum key distribution anti-noise system is provided, comprising a receiving end and a sending end;

[0021] The receiving end obtains channel state, calculates channel noise power spectrum and finds the position of the lowest channel noise power, denoted as window, and the sending end moves the transmission signal spectrum to the window for transmission;

[0022] The receiving end moves the received signal spectrum back to baseband, and then filters the received signal using a low-pass filter to retain the transmission signal.

[0023] Preferably, the receiving end calculates the channel noise power spectrum and finds the local minimum value therein, denoted as a window, and feeds back the window information to the sending end, and the sending end shifts the spectrum of the transmission signal according to the received window information to the window position.

[0024] Preferably, the receiving end shifts the spectrum of the signal received from the sending end back to the baseband together with the received noise, and filters the signal shifted back to the baseband through a low-pass filter to filter out the noise outside the passband and reserve the transmission signal within the passband.

[0025] Preferably, the amplitude characteristic of the low-pass filter is:

[0026]

[0027] wherein |H(jω)| is the amplitude characteristic of the low-pass filter, ω is the frequency, ω c is the 3dB cutoff frequency, and N is the order of the low-pass filter.

[0028] Preferably, the low-pass filter is a Butterworth low-pass filter.

[0029] Compared with the prior art, the present application has the following beneficial effects:

[0030] The present application combines the frequency switching idea with the filter, avoids the transmission signal from being submerged by the channel noise, is beneficial to reduce the noise components received by the receiving end of the continuous variable quantum key distribution system as much as possible, can effectively reduce the over noise in the system, and improves the system key rate. BRIEF DESCRIPTION OF DRAWINGS

[0031] Other features, objects and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments with reference to the attached drawings:

[0032] Figure 1 is a flowchart of the present application. DETAILED DESCRIPTION

[0033] The present application will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present application. These all belong to the protection scope of the present application.

[0034] In order to avoid the quantum signal in the continuous variable quantum key distribution system from being interfered by the large power random noise, so that the receiving end cannot correctly identify, the application designs a continuous variable quantum key distribution anti-noise method based on frequency switching, separates the transmission signal from the noise, and reduces the noise components received together with the transmission signal at the receiving end as much as possible, and improves the problem that the continuous variable quantum key distribution system is too noisy and the key rate is reduced due to the random noise.

[0035] The noise in the quantum channel can be mainly divided into two categories, namely, trusted noise and untrusted noise. The noise such as thermal noise and shot noise, which appears as long as the system is running and has a constant power spectrum, is considered as trusted noise; and other noise introduced by external interference is considered as untrusted noise. The untrusted noise is characterized in that the frequency spectrum appears at a random position and the noise power is also random. If the frequency spectrum of the untrusted noise appears at the position of the transmission signal spectrum, the transmission signal will be submerged, which affects the subsequent reception of the signal, so it is necessary to separate the transmission signal from the noise. Since the channel noise spectrum has fluctuations, the application first uses the frequency switching mode to move the transmission signal spectrum to a frequency band where the noise spectrum amplitude is generally low, and then adds a filter at the receiving end, so that the transmission signal spectrum passes through the passband of the filter, and the noise outside the passband is filtered out, so as to achieve the purpose of reducing the influence of noise on the receiving end as much as possible.

[0036] The operation steps of the application are as follows:

[0037] Frequency switching. The channel noise spectrum with random noise has large fluctuations, and the frequency band with the lowest spectrum amplitude is recorded as a window. The sending end moves the spectrum of the transmission signal to the window position and sends it to the receiving end, so as to separate the transmission signal from the noise.

[0038] Optimal filtering. The receiving end moves the received signal from the window position to the baseband, and passes the spectrum-moved signal through a low-pass filter, so that the spectrum of the transmission signal passes through the passband, and the noise components on other frequency bands are filtered out, so that the receiving end can receive the correct transmission signal.

[0039] As shown in Figure 1 , a continuous variable quantum key distribution anti-noise method based on frequency switching comprises:

[0040] (1) The receiving end acquires the channel state. The receiving end estimates the channel state and acquires the channel noise spectrum without transmission signal. Since the spectrum has strong randomness, in order to obtain correct window information, the receiving end calculates the power spectrum of the channel noise.

[0041] (2) Obtain the window position. According to the obtained channel noise power spectrum, search for a local minimum value in the power spectrum, and mark the local minimum value as a window. Find the frequency position corresponding to the window, and feed back the position information to the sending end.

[0042] (3) Perform frequency switching on the transmission signal. After the sending end obtains the window information, shift the transmission signal spectrum to the window position, and send to the receiving end.

[0043] (4) Optimal filtering. Set a Butterworth low-pass filter at the receiving end. Before filtering, shift the received signal (containing the transmission signal and channel noise) spectrum from the window position back to the baseband. The signal after the spectrum is shifted back to the baseband passes through the Butterworth low-pass filter, and the filter retains the transmission signal spectrum located at the baseband and a small amount of noise, and filters out the noise components outside the passband. The receiving end can accurately extract the transmission signal, avoiding the situation that the transmission signal cannot be correctly received by the receiving end under random noise interference.

[0044] The amplitude characteristic of the Butterworth low-pass filter can be represented as:

[0045]

[0046] where |H(jω)| is the amplitude characteristic of the Butterworth filter, ω is the frequency, ω c is the 3dB cutoff frequency, and N is the order of the Butterworth filter.

[0047] (5) Repeat steps (1)-(4) after a certain period of time. Since the channel noise is random, the channel state may change after a period of time, and the actual window position may also change. If the transmission signal spectrum cannot be shifted to the correct window position, the signal will be overwhelmed by noise. In order to stabilize the performance of the continuous variable quantum key distribution system, it is necessary to update the position of the window at a certain time interval.

[0048] The application also provides a continuous variable quantum key distribution anti-noise system based on frequency switching, comprising a receiving end and a sending end. The receiving end obtains the channel state, calculates the channel noise power spectrum, and finds the position with the lowest channel noise power, which is marked as a window. The sending end shifts the transmission signal spectrum to the window for transmission. The receiving end shifts the received signal spectrum back to the baseband, and then uses a low-pass filter to filter the received signal, and retains the transmission signal.

[0049] Specifically, the receiving end calculates the channel noise power spectrum and finds the local minimum value therein, denoted as window, and feeds back the window information to the sending end, and the sending end shifts the spectrum of the transmission signal according to the received window information to the window position. After receiving the signal from the sending end, the receiving end shifts the signal spectrum together with the received noise back to the baseband, and filters the signal shifted back to the baseband through a low-pass filter to filter out the noise outside the passband and retain the transmission signal within the passband.

[0050] The low-pass filter adopts a Butterworth low-pass filter, and the amplitude characteristic can be represented as:

[0051]

[0052] wherein |H(jω)| is the amplitude characteristic of the Butterworth filter, ω is the frequency, ω c is the 3dB cutoff frequency, and N is the order of the Butterworth filter.

[0053] Those skilled in the art understand that, in addition to implementing the system provided by the present application and each device, module and unit thereof in the form of pure computer readable program code, the system provided by the present application and each device, module and unit thereof can also be implemented in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers and embedded microcontrollers, etc. by logically programming the method steps to achieve the same functions. Therefore, the system provided by the present application and each device, module and unit thereof can be considered as a hardware component, and the devices, modules and units included therein for achieving various functions can also be considered as structures within the hardware component; the devices, modules and units for achieving various functions can also be considered as both software modules for implementing the method and structures within the hardware component.

[0054] The specific embodiments of the present application are described above. It should be understood that the present application is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essential content of the present application. The embodiments of the present application and the features in the embodiments can be combined with each other in any manner without conflict.

Claims

1. A noise-resistant method for continuous-variable quantum key distribution based on frequency switching, characterized in that, include: Frequency switching steps: Obtain the channel state, calculate the channel noise power spectrum and find the position with the lowest channel noise power as the window, and move the transmission signal spectrum of the transmitting end to the window for transmission; Optimal filtering steps: Move the spectrum of the signal received at the receiving end back to the baseband, and then use a low-pass filter to filter the received signal while retaining the transmitted signal; The frequency switching steps include: Step A1: The receiving end acquires the channel status; Step A2: The receiver calculates the channel noise power spectrum, finds the local minimum value and records it as a window, and feeds back the window information to the transmitter; Step A3: The transmitting end shifts the spectrum of the transmitted signal to the window position according to the received window information; The optimal filtering steps include: Step B1: After receiving the signal from the transmitter, the receiver moves the signal spectrum along with the received noise back to the baseband. Step B2: Pass the signal brought back to baseband through a low-pass filter to remove noise outside the passband and retain the transmitted signal within the passband.

2. The noise-resistant method for continuous variable quantum key distribution based on frequency switching according to claim 1, characterized in that, The amplitude characteristics of the low-pass filter are as follows: Where |H(jω)| is the amplitude characteristic of the low-pass filter, ω is the frequency, and ω c The cutoff frequency is 3dB, and N is the order of the low-pass filter.

3. The noise-resistant method for continuous variable quantum key distribution based on frequency switching according to claim 1, characterized in that, The low-pass filter is a Butterworth low-pass filter.

4. A noise-resistant continuous-variable quantum key distribution system based on frequency switching, characterized in that, Includes: receiver and transmitter; The receiving end acquires the channel state, calculates the channel noise power spectrum, and finds the position with the lowest channel noise power, which is recorded as a window. The transmitting end moves the transmission signal spectrum to the window for transmission. The receiving end moves the received signal spectrum back to the baseband, and then uses a low-pass filter to filter the received signal, retaining the transmitted signal; The receiver calculates the channel noise power spectrum and finds the local minimum value as the window. It feeds back the window information to the transmitter. The transmitter then shifts the spectrum of the transmitted signal to the window position based on the received window information. After receiving the signal from the transmitter, the receiver moves the signal spectrum along with the received noise back to the baseband. The signal moved back to the baseband is then passed through a low-pass filter to filter out noise outside the passband and retain the transmitted signal within the passband.

5. The noise-resistant system for continuous variable quantum key distribution based on frequency switching according to claim 4, characterized in that, The amplitude characteristics of the low-pass filter are as follows: Where |H(jω)| is the amplitude characteristic of the low-pass filter, ω is the frequency, and ω c The cutoff frequency is 3dB, and N is the order of the low-pass filter.

6. The noise-resistant system for continuous variable quantum key distribution based on frequency switching according to claim 4, characterized in that, The low-pass filter is a Butterworth low-pass filter.

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