Quantum coder and decoder of phase modulated polarizing state and its application method

Abstract

The present invention relates to a quantum coder and decoder with phase modulated polarization state and their application method in the quantum secure communication. Four-state quantum coder or decoder is formed from a phase-polarization controller and a ture random generator, and can implement quantum secure communication using "two linear polarization states and two circular polarization states" four-state coded BB84 protocol; and six-state quantum coder or decoder is formed from two phase-polarization controllers and a synchronous trigger, and can implement six-state coded quantum secure communication.

Description

technical field [0001] The invention relates to a quantum secret communication method used in the BB84 protocol in the communication field. Background technique [0002] In the existing quantum secure 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 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 in...

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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.

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