Parameters adaptive adjustment strategy of quantum communication channel in free-space based on software-defined quantum communication

Abstract

Quantum communication in free space will be disturbed by natural environment, such as fog, dust, and rain, which is a difficult problem in the construction of quantum communication system. In order to solve this problem and improve the survivability of quantum communication system, we propose an adaptive parameter adjustment strategy for free-space quantum communication based on software-defined quantum communication (SDQC). Firstly, we propose a software-defined quantum communication model based on the idea of software defined networks. The architecture of SDQC is divided into four layers: transport layer, access layer, control layer, and management layer. The SDQC system sends the link information to the preset program at a management level through the real-time monitoring of channel state by the access layer. According to the link information, the management level issues instructions to the control layer to adjust the parameters such as the initial quantum state and the existence time of single quantum state, in order to improve the quantum entanglement and fidelity. Secondly, we analyze the relationship between quantum fidelity and parameters in SDQC system under three noise channels, i.e. depolarization channel, spontaneous amplitude decay channel, and phase damping channel. In the depolarized channel, the quantum fidelity <i>F</i> decreases with the increase of the error probability <i>P</i><sub>d</sub> of the qubit. When the error probability of qubit is certain, the system has the maximum quantum fidelity with the value of parameter <i>x</i> is 0.5. In the spontaneous amplitude decay channel, the quantum fidelity <i>F</i> decreases with the increase of the quantum state transition probability <i>p</i><sub>t</sub>. When the transition probability of quantum state is certain, the higher the value of parameter <i>x</i>, the higher the fidelity will be. In the phase-damped channel, the quantum fidelity <i>F</i> decreases with the increase of the probability <i>p</i><sub>c</sub> with which the qubit and the background interference equivalent quantum state have complete elastic scattering. When the probability is certain, the larger the value of |1/2 – <i>x</i>|, the higher the quantum fidelity of the system will be. Finally, we study the optimal values of SDQC system parameters under different environmental disturbances. The simulation results show that the optimal parameters of SDQC system are different when the parameters of three noise channels, namely depolarization, spontaneous amplitude decay and phase damping, are different. The system adaptively selects the initial quantum state and the existence time of single quantum state according to the environmental change and business demand, so that the quantum fidelity is always at the peak in the communication process. This strategy effectively improves the adaptability and comprehensive immunity of the quantum communication system.