Abstract
Entanglement distribution between distant parties is an essential component to most quantum communication protocols. Unfortunately, decoherence effects such as phase noise in optical fibres are known to demolish entanglement. Iterative (multistep) entanglement distillation protocols have long been proposed to overcome decoherence, but their probabilistic nature makes them inefficient since the success probability decays exponentially with the number of steps. Quantum memories have been contemplated to make entanglement distillation practical, but suitable quantum memories are not realised to date. Here, we present the theory for an efficient iterative entanglement distillation protocol without quantum memories and provide a proof-of-principle experimental demonstration. The scheme is applied to phase-diffused two-mode-squeezed states and proven to distil entanglement for up to three iteration steps. The data are indistinguishable from those that an efficient scheme using quantum memories would produce. Since our protocol includes the final measurement it is particularly promising for enhancing continuous-variable quantum key distribution.
Highlights
Entanglement distribution between distant parties is an essential component to most quantum communication protocols
The hardware-efficient pumping Gaussifier proposed in ref. 19 requires only a single quantum memory unit on each side, and enables sequential processing of the individual copies of distilled quantum state but achieves inefficient distillation rate as a purely optical scheme without quantum memory
The starting point of our work is the iterative Gaussification scheme[24,25] illustrated in Fig. 1, which can serve for entanglement distillation of non-Gaussian quantum states of light
Summary
Entanglement distribution between distant parties is an essential component to most quantum communication protocols. All elementary two-copy distillation steps need to succeed simultaneously, which imposes an exponential overhead in terms of required resources, and drastically reduces the success rate of the protocol. Single-copy entanglement concentration[10,13,14,16,20], and elementary two-copy entanglement distillation[11,12] have been demonstrated for both discrete- and continuous-variable quantum states of light. Aside from this, an efficient realization of the full iterative multicopy entanglement distillation protocol could never be done because it is pending on operating an efficient quantum memory We address this challenge from an opposite viewpoint and cancel out the need for quantum memories by exploiting the recently proposed concept of emulation of a quantum protocol[21,22]. The emulation of noiseless quantum amplification and attenuation by processing the data resulting from (eight-port) homodyne detection was proposed[21,22], and a proof-of-principle experimental emulation of single-mode noiseless quantum amplification was reported[23]
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