Advantages of the coherent state compared with squeezed state in unidimensional continuous variable quantum key distribution

Abstract

In this work, a comparison study between unidimensional (UD) coherent-state and UD squeeze-state protocols is performed in the continuous variable quantum key distribution domain. First, the UD squeeze-state protocol is proposed, and the equivalence between the prepare-and-measure and entanglement-based schemes of UD squeezestate protocol is proved. Then, the security of the UD squeeze-state protocol under collective attack in realistic conditions is analyzed. Lastly, the performances of the two UD protocols are analyzed. Based on the uniform expressions established in our study, the squeeze-state and coherent-state protocols can be analyzed simultaneously. Our results show that the UD squeeze-state protocols are quite different from the two-dimensional (TD) protocols in that the UD squeeze-state protocols have a poorer performance compared with UD coherent-state protocols, which is opposite in the case of TD protocols. PACS number(s): 03.67.Dd, 03.67.Hk I. INTRODUCTIONThe unconditional security of quantum key distribution (QKD) prevents information from being eavesdropped; it is expected that this technology will be used for a wide variety of applications in the future with the advent of quantum information technology. In general, QKD technology can be categorized into discrete-variable and continuousvariable (CV) QKD protocols [1-2]. CV-QKD protocols encode information into continuous quadrature components of quantum states and utilize homodyne detectors instead of single-photon detectors. The CV-QKD protocols typically provide a high secret key rate at a relatively short distance; in addition, they have good compatibility with the classical communication networks . Based on the utilized quantum states, the CV-QKD protocols can be classified as coherent-state protocols, squeezestate protocols, and entanglement-state protocols. In general, it is believed that the squeeze-state and entanglementstate protocols perform better than the coherent-state protocols; however, because coherent state sources are easy to prepare, coherent-state protocols have also been widely researched. Till date, many protocols to enhance the performance of or simplify a QKD system have been proposed, including a unidimensional (UD) coherent-state protocol [26], three coherent-state protocols [27], and method for passive state preparation [28]. The advantages of the UD coherent-state protocol include easy modulation, low costs, and only needs less random numbers [29,30]. In the case of a small amount of excess noise, the UD coherent-state protocol performs as well as the two-dimensional (TD) coherent-state protocol (GG02). Therefore, the UD coherent-state protocol has the potential to be used for applications in various scenarios, such as in QKD local area networks, where the transmission distance between users is typically short and cost is a key concern.Thus far, the UD modulation method has only focused on the coherent-state protocol. Therefore, in this study, a UD squeeze-state protocol was proposed; in addition, the equivalence betwee...

Improvement of unidimensional continuous-variable quantum key distribution systems by using a phase-sensitive amplifier

“…The PM scheme and the entanglement-based (EB) scheme of the UD CV-QKD protocol using coherent states are illustrated separately in figure 2(a) and figure 2(b). The equivalence between the two schemes in the UD CV-QKD protocols has been proved in [27], and the detailed calculation process of secret key rates can be found in [25].…”

“…Compared with the Gaussian-modulated protocols, the features of the UD CV-QKD protocols include easy modulation, low cost, and only a small number of random numbers required [26]. Moreover, the performance of the UD coherent-state CV-QKD protocol is comparable to the Gaussian-modulated coherent-state protocol under the condition of low thermal excess noise [27]. Therefore, the UD CV-QKD protocol using coherent states has a clear potential for application to various scenarios.…”

Security analysis of unidimensional continuous-variable quantum key distribution with discretized amplitude modulation

“…This asymmetric modulation can effectively simplify the implementation at the transmitter and significantly enhance the practicability of CVQKD. Recently, while original UD-CVQKD protocol has been studied in-depth both theoretically and experimentally [15][16][17][18][19], the scheme is further generalized to the squeezed state case [20,21] as well as the discrete modulation scheme [22]. In addition, the unidimensional continuous variable measurementdevice-independent QKD (CV-MDI QKD) protocol [23] and the unidimensional two-way CVQKD protocol [24] were proposed to simplify the system realization.…”

Photon Subtraction-Induced Plug-and-Play Scheme for Enhancing Continuous-Variable Quantum Key Distribution with Discrete Modulation

“…Quantum key distribution (QKD) [1][2][3] is a primary application of quantum cryptography, which enables two remote legitimate communication parties, Alice and Bob, to share random secret key sequences [4][5][6] in public channel preventing the eavesdropper Eve by physical laws [7][8][9][10]. There are two research fields for QKD, i.e., discrete-variable QKD(DVQKD) and continuous-variable QKD (CVQKD) [11][12][13][14]. In DVQKD, information is encoded on properties of single photon, and it uses single-photon detector at the receiver side.…”