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arXiv:quant-ph/0003116 · Physical Review A

Physical implementation for entanglement purification of Gaussian continuous-variable quantum states

L.-M. Duan, G. Giedke, J. I. Cirac, P. Zoller

Published Aug 14, 2000• 43 citations
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Abstract

We give a detailed description of the entanglement purification protocol which generates maximally entangled states with high efficiencies from realistic Gaussian continuous variable entangled states. The physical implementation of this protocol is extensively analyzed using high finesse cavities and cavity enhanced cross Kerr nonlinearities. In particular, we take into account many imperfections in the experimental scheme and calculate their influences. Quantitative requirements are given for the relevant experimental parameters.

DOI
10.1103/physreva.62.032304

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We give a detailed description of the entanglement purification protocol which generates maximally entangled states with high efficiencies from realistic Gaussian continuous variable entangled states. The physical implementation of this protocol is extensively analyzed using high finesse cavities and cavity enhanced cross Kerr nonlinearities. In particular, we take into account many imperfections in the experimental scheme and calculate their influences. Quantitative requirements are given for the relevant experimental parameters.
Summary form only given. One of the key elements of quantum communication is the generation of maximally entangled states between distant nodes of a quantum network. We present an entanglement purification scheme which generates maximally entangled states in finite Hilbert spaces from the continuous two-mode squeezed states. With high probabilities, we get a more entangled stale, and the entanglement in the continuous partially entangled state is transferred to the maximally entangled states with high efficiency. Furthermore, in several practical cases this purification protocol can be readily extended to distill maximally entangled states from the mixed Gaussian continuous states.
In our previous paper [D. Gon\ifmmode \mbox{\c{t}}\else \c{t}\fi{}a and P. van Loock, Phys. Rev. A 84, 042303 (2011)], we proposed an efficient scheme to purify dynamically a bipartite entangled state using short chains of atoms coupled to high-finesse optical cavities. In contrast to conventional entanglement purification protocols, we avoid controlled-not gates and thus reduce complicated pulse sequences and superfluous qubit operations. In this paper, we significantly improve the output fidelity of remotely entangled atoms by introducing one additional entanglement protocol in each of the repeater nodes and by optimizing the laser beams required to control the entire scheme. Our improved distillation scheme yields an almost-unit output fidelity that, together with the entanglement distribution and swapping, opens an attractive route towards an efficient and experimentally feasible quantum repeater for long-distance quantum communication.
We propose schemes for entanglement concentration and purification for qubit systems encoded in flying atomic pairs. We use cavity-quantum electrodynamics as an illustrative setting within which our proposals can be implemented. Maximally entangled pure states of qubits can be produced as a result of our protocols. In particular, the concentration protocol yields Bell states with the largest achievable theoretical probability while the purification scheme produces arbitrarily pure Bell states. The requirements for the implementation of these protocols are modest, within the state of the art, and we address all necessary steps in two specific setups based on experimentally mature microwave technology.
We present a proposal for entanglement purification of the continuous-variable quantum state of two propagating optical fields. The scheme is based on each field interacting with a local node-atomic ensemble whose internal collective excitation plays the role of an ancillary continuous-variable resource. Entanglement purification is achieved by a dichotomic measurement, representing the required non-Gaussian element, which consists of detecting the presence or absence of collective excitations in the atomic ensemble. This scheme can be extended to networks, where the nodes are single trapped atoms, and constitutes an important building block for the implementation of a continuous-variable quantum repeater.