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Quantum encoder whose polarization state is modulated by phase and decoder and its application

A phase modulator and quantum encoding technology, applied in the field of polarization compensation, can solve problems such as difficulty in high-speed encoding, halving of efficiency, and difficulty in generating entangled photons

Inactive Publication Date: 2005-10-19
SOUTH CHINA NORMAL UNIVERSITY
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Problems solved by technology

[0003] The BB84 protocol usually adopts the phase modulation encoding method, that is, two identical Mach-Zehnder interferometers are used as the encoder and decoder. The bit error rate of this encoding method is mainly determined by the interference contrast ratio of the Mach-Zehnder interferometer in addition to the electrical noise. decision, and the interference contrast is determined by the coherence of light, because the coherence of light is inevitably destroyed in the process of modulation and transmission, and once the coherence is destroyed, it cannot be compensated, therefore, the bit error rate of this coding method relatively high
[0004] Although the BB84 protocol can also be implemented using four non-orthogonal linear polarization states or a four-state encoding method of two linear polarizations plus two circular polarization states, there is still no breakthrough in technology.
[0005] The B92 protocol usually has two methods of phase modulation and polarization modulation. The phase modulation coding method is basically the same as the BB84 protocol, except that the B92 protocol uses binary coding, and the efficiency is halved; while the polarization modulation coding method usually uses two linear polarization states of photons. Coding, that is, using electro-optic crystals (such as KD * P, LiNbO 3 etc.) or the Pockels cell modulates and encodes the two linear polarization states of the photon. Because the half-wave voltage of the electro-optic crystal or the Pockels cell is very high (several thousand volts), it is very inconvenient to use, and it is difficult to achieve high-speed encoding, especially for optical The polarization state of the fiber is easily affected by factors such as stress birefringence and polarization mode dispersion in the fiber during transmission, as well as environmental interference, so the bit error rate is relatively high
[0006] The E91 protocol uses entangled photons for encoding. Because it is difficult to generate entangled photons, the required equipment is relatively expensive, and it is difficult to popularize and apply.

Method used

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  • Quantum encoder whose polarization state is modulated by phase and decoder and its application
  • Quantum encoder whose polarization state is modulated by phase and decoder and its application
  • Quantum encoder whose polarization state is modulated by phase and decoder and its application

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Embodiment 1

[0038] Embodiment 1: Carry out quantum cryptography communication of BB84 protocol with four-state quantum encoder and decoder

[0039] For the first time, we have experimentally realized the quantum cryptography communication of the BB84 protocol using the 4-state encoding method of "two linear polarization states plus two circular polarization states". Optical path such as image 3 As shown, the method is as follows: the sender uses a four-state quantum encoder to randomly prepare photons of four non-orthogonal polarization states, and transmits them to the receiver through an optical fiber, and the receiver uses a four-state quantum decoder to randomly generate four groups of non-orthogonal polarization states Polarization state measurement base, which detects the four non-orthogonal polarization state photons sent by the sender. When a photon is detected, the receiver sends the measurement base used to the sender through a public channel, and the sender tells the receiver ...

Embodiment 2

[0040] Embodiment 2: Use a six-state quantum encoder and a decoder to perform six-state encoded quantum cryptography communication.

[0041] For the first time, we have carried out six-state quantum cryptography communication with six-state encoding, and the optical path is as follows Figure 5 As shown, the sender uses a six-state quantum encoder to randomly prepare photons of six non-orthogonal polarization states, and transmits them to the receiver through an optical fiber, and the receiver uses a six-state quantum decoder to randomly generate six non-orthogonal polarization states for measurement base, to detect the six non-orthogonal polarization state photons sent by the sender. In the case of detecting photons, the receiver sends the measurement base used to the sender through a public channel, and the sender tells the receiver which measurement bases are selected. By the way, then the sender and the receiver keep the corresponding bits when the measurement base is cons...

Embodiment 3

[0042] Embodiment 3: Polarization Compensation by Phase Modulation of Polarization State

[0043] For the first time, we used the method of phase-modulating the polarization state to Figure 4 , Figure 5 The communication line shown has carried out the polarization compensation experiment, and the method is as follows: the sender sends a standard 45° linearly polarized photon to the receiver, and the receiver uses a 135° linear polarization measurement base to detect (according to Table 1, V 1 =V 0 / 2, V 2 =V 0 / 2, can produce this kind of measurement basis), if the polarization state of the photon does not change during the transmission process, then the receiver cannot measure the photon, if the photon depolarizes during the transmission process, for example, it becomes a right-handed ellipse polarized light, then the receiver may measure the photons, at this time, the receiver only needs to change V 1 voltage, making it in Fine-tuning is performed within the range u...

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Abstract

The present invention relates to a quantum coder with phase modulated polarization state, decoder and polarization compensating method used in the quantum secret communication, four-state quantum coder and decoder are formed from a phase-polarization controller and a true random generator, and the six-state quantum coder and decoder are formed from two phase-polarization controllers and a synchronous trigger, in the quantum secret communication it utilizes the quantum coder and decoder to effectively compensate the polarization state distortion resulted in the course of signal transmission, so that its error code rate can be greatly reduced to 10 to the minus fifth, and its modulation speed can be up to several GHz from tens Hz.

Description

technical field [0001] The invention relates to special equipment for quantum secure communication in the communication field and an application method thereof, in particular to a quantum encoder and decoder for phase modulation polarization state and a polarization compensation method for quantum secure communication. Background technique [0002] In the existing quantum cryptography communication technology, there are three types of protocols such as BB84 protocol, B92 protocol and E91 protocol, and three coding methods such as two-state coding, four-state coding and six-state coding. The BB84 protocol belongs to the four-state coding method, while the B92 protocol and the E91 protocol belong to the two-state coding method. The efficiency of the four-state coding method is relatively high, while the efficiency of the two-state coding method is halved. [0003] The BB84 protocol usually adopts the phase modulation encoding method, that is, two ide...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): G02B6/27G02B6/28G09C1/00H04J14/06H04K1/00H04L9/00
Inventor 唐志列廖常俊刘颂豪
Owner SOUTH CHINA NORMAL UNIVERSITY
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