Zhuang Quntao
Department of Electrical and Computer Engineering and James C. Wyant College of Optical Sciences, University of Arizona, Tucson, Arizona 85721, USA.
Phys Rev Lett. 2021 Feb 12;126(6):060502. doi: 10.1103/PhysRevLett.126.060502.
A phase reference has been a standard requirement in continuous-variable quantum sensing and communication protocols. However, maintaining a phase reference is challenging due to environmental fluctuations, preventing quantum phenomena such as entanglement and coherence from being utilized in many scenarios. We show that quantum communication and entanglement-assisted communication without a phase reference are possible, when a short-time memory effect is present. The degradation in the communication rate of classical or quantum information transmission decreases inversely with the correlation time. Exact solutions of the quantum capacity and entanglement-assisted classical and quantum capacity for pure dephasing channels are derived, where non-Gaussian multipartite-entangled states show strict advantages over usual Gaussian sources. For thermal-loss dephasing channels, lower bounds of the capacities are derived. The lower bounds also extend to scenarios with fading effects in the channel. In addition, for entanglement-assisted communication, the lower bounds can be achieved by a simple phase-encoding scheme on two-mode squeezed vacuum sources, when the noise is large.
在连续变量量子传感和通信协议中，相位参考一直是一项标准要求。然而，由于环境波动，维持相位参考具有挑战性，这使得诸如纠缠和相干等量子现象在许多场景中无法得到利用。我们表明，当存在短时记忆效应时，无需相位参考的量子通信和纠缠辅助通信是可行的。经典或量子信息传输的通信速率下降与相关时间成反比。推导了纯退相通道的量子容量以及纠缠辅助经典和量子容量的精确解，其中非高斯多体纠缠态相对于通常的高斯源具有严格优势。对于热损耗退相通道，推导了容量的下限。这些下限也适用于具有信道衰落效应的场景。此外，对于纠缠辅助通信，当噪声较大时，通过对双模压缩真空源进行简单的相位编码方案即可达到下限。
