Distribution of a modulated squeezed state over a lossy channel

Shuhong Hao Shuhong Hao, Xiaowei Deng Xiaowei Deng, Qiang Zhang Qiang Zhang, and Xiaolong Su and Xiaolong Su
2015 Chinese Optics Letters (COL)  
The distribution of a modulated squeezed state over a quantum channel is the basis for quantum key distribution (QKD) with a squeezed state. In this Letter, a modulated squeezed state is distributed over a lossy channel. The Wigner function of the distributed state is measured to observe the evolution of the quantum state over a lossy channel, which shows that the squeezing level and the displacement amplitude of the quantum state are decreased along with the increase of the channel loss. We
more » ... channel loss. We also measure the squeezing level in the frequency domain by the frequency shift technique. The squeezing of the modulated squeezed state at the modulation frequency is observed in this way. The presented results supply a reference for a QKD with a squeezed state. Quantum key distribution (QKD) allows two legitimate parties, Alice and Bob, who are linked by a quantum channel and an authenticated classical channel, to establish a secret key only known to themselves. Continuous variable (CV) QKD using a Gaussian quantum resource state, such as the entangled state, squeezed state, or coherent state, as the resource state, along with reconciliation and a privacy amplification procedure, can distill the secret key [1] . Recently, quantum discord has also been applied to complete QKD [2, 3] . CV QKDs exploiting the coherent state [4] [5] [6] [7] [8] [9] [10] and the entangled state [11] [12] [13] have been experimentally realized in recent years. In the proposed QKD scheme with the squeezed state [14] [15] [16] [17] [18] , squeezed states that are randomly displaced along the squeezed quadrature, which is obtained by modulating the squeezed states, are transmitted from Alice to Bob. Bob performs homodyne or heterodyne detection on the received quantum state. Then, Alice and Bob use the classical data process, such as post-selection, reconciliation (reverse reconciliation), and privacy amplification, to distill the secret key [1] . Loss and excess noise in the quantum channel are two parameters that limit the secret key rate and transmission distance of the CV QKD scheme. It has been shown that QKD based on the squeezed state and heterodyne detection can tolerate more excess noise than a QKD scheme with the coherent state [17] . Recently, a squeezed state was distributed through an atmospheric channel, which supplies a reference for free-space CV QKD with the squeezed state [19] . The distribution of modulated squeezed states over a quantum channel is the precondition for a QKD with the squeezed state. What we are concerned with is the squeezing property of the modulated squeezed state after it is transmitted through a lossy channel. In this Letter, COL 13(12), 122701(2015) CHINESE OPTICS LETTERS
doi:10.3788/col201513.122701 fatcat:3e6ct7ahnra7tadczg7hkdsy74