Experimental demonstration of post-selection-based continuous-variable quantum key distribution in the presence of Gaussian noise

Abstract

In realistic continuous variable quantum key distribution protocols, an eavesdropper may exploit the additional Gaussian noise generated during transmission to mask her presence. We present a theoretical framework for a post-selection based protocol which explicitly takes into account excess Gaussian noise. We derive a quantitative expression of the secret key rates based on the Levitin and Holevo bounds. We experimentally demonstrate that the post-selection based scheme is still secure against both individual and collective Gaussian attacks in the presence of this excess noise.PACS numbers: 03.67. Dd, 42.50.Dv, 89.70.+c Continuous variable quantum key distribution (CV-QKD) [1] was introduced as an alternative to the original discrete variable single photon schemes [2]. CV-QKD promises to offer higher secret key rates, better detection efficiencies and higher bandwidths than its single photon counterpart and is easily adapted to current communication systems. Currently the two main protocols in CV-QKD are post-selection (PS) [3] and reverse reconciliation (RR) [4]. These protocols are based on the random Gaussian modulation of coherent states using either homodyne [4] or heterodyne [5] detection and both have been experimentally demonstrated [6,7,8,9,10]. At present PS-based CV-QKD has practical advantages in terms of key distillation and has been demonstrated experimentally for up to 90% channel loss [7].Reverse reconciliation CV-QKD, due to its inherent nature, easily incorporates excess noise into the protocols, and security proof have been demonstrated in the case of individual Gaussian attacks [4,5], non-Gaussian attacks [11], collective attacks [12,13] (with their Gaussian optimality [14]) and coherent states using homodyne detection [15]. For PS CV-QKD, the addition of excess noise into the analysis is quite difficult. The original protocol [3] only considered pure or vacuum states in its scheme and so far all post-selection protocols since have concentrated on the unrealistic case of zero excess noise [7,16,17]. Recently however, excess noise using a hybrid protocol, consisting of both post-selection and either direct or reverse reconciliation, was considered for the case of collective attacks [18].In this paper, we present a protocol for calculating the effect of excess Gaussian noise (EGN) on post-selection where two way classical communication is permitted, and show its security when considering either individual or collective attacks. We apply our analysis to an experimental demonstration and conclude that good key rates can be obtained under the realistic condition of channel with loss and excess Gaussian noise.We extend the original PS CV-QKD protocol [3] as follows. The sender, Alice draws two random numbers S x A and S p A from Gaussian distributions of variances V x A and V p A re-AM

Gaussian quantum information

“…Therefore, a subtler analysis has to be carried out to obtain tighter bounds. Here we present the basic security analysis for the postselection protocol against collective entangling cloner attacks (Heid and Lütkenhaus, 2007;Symul et al, 2007). When Bob performs homodyne detection, the mutual information between Alice and Bob for a given pair of variables (|a q(p) |, |b|) is given by Shannon's formula for a binary channel (Shannon, 1948) I(a : b) = 1 + p e log p e + (1 − p e ) log(1 − p e ) .…”

Continuous-variable quantum key distribution in non-Markovian channels

“…Different proposals for CV QKD have been put forward, either based on singlemode coherent [3,4] and squeezed [5][6][7][8][9][10][11] signals or EinsteinPodolsy-Rosen (EPR) correlated beams [12,13]. Experimental demonstrations have been reported for coherent [3,4,[14][15][16], squeezed [10], and EPR beams-based [13] protocols, and unconditional security proofs have also been investigated [17,18].…”

Partially random phase attack to the practical two-way quantum-key-distribution system

“…The homodyne detection is a well-established quantitative method to measure the quadrature-amplitude operator of the signal field [27,28] or implement the continuous variable quantum cryptography [29,30]. A simple illustration of the homodyne detection is shown in Fig.…”