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Journal of the Optical Society of America B

Optimal atomic entanglement concentration using coherent-state input–output process in low-Q cavity quantum electrodynamics system

Cong Cao, Chuan Xi Wang, Lingyan He, Xin Tong, Ming Lei, Ru Zhang

Published Jul 16, 2013• 7 citations
Publisher

Abstract

This paper presents an optimal entanglement concentration protocol (ECP) for entangled solid-state systems, using the coherent-state input–output process working in the low-Q cavity quantum electrodynamics regime. The solid-state system can be described as a three-level atom confined in a one-side optical microcavity. Using the ancillary coherent optical pulse to perform the cavity input–output process, different state-dependent phase shifts of the output coherent state can be discriminated by homodyne detection, and a less-entangled atomic pair can be concentrated to maximally entangled state in a certain probability between two remote parties nonlocally. By repeating the concentration process, the remote parties can further obtain a higher success probability. Compared with conventional ECPs, only one pair of less-entangled atoms is needed in the proposed protocol, and the coherent-state input–output process is working in a low-Q cavity in the atom–cavity intermediate coupling region. With feasible technologies, this protocol may be widely used in quantum repeaters and long-distance quantum communication.

DOI
10.1364/josab.30.002136

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We put forward an optimal entanglement concentration protocol (ECP) for recovering an arbitrary less-entangled multi-photon Greenberger–Horne–Zeilinger (GHZ) state into the maximally entangled GHZ state based on the photonic Faraday rotation in low-quality ( Q ) cavity. In the ECP, only one pair of less-entangled multi-photon GHZ state and one auxiliary photon are required, and the concentration task can be realized by local operations. Moreover, our ECP can be used repeatedly to further concentrate the discarded items of conventional ECPs, which can increase its success probability largely. Under the practical imperfect detection condition, our protocol can still work with relatively high success probability. This ECP has application potential in current and future quantum communication.
We present an efficient entanglement concentration protocol (ECP) for the less-entangled W state with some identical conventional polarized single photons. In the protocol, two of the parties say Alice and Charlie should perform the parity check measurements and they can ultimately obtain the maximally entangled W state with a certain success probability Otherwise, they can obtain another less-entangled W state, which can be reconcentrated into the maximally entangled W state. By iterating this ECP, a high success probability can be achieved. This ECP may be an optimal one and it is useful in current quantum information processing.
We present two realistic entanglement concentration protocols (ECPs) for pure partially entangled photons. A partially entangled photon pair can be concentrated to a maximally entangled pair with only an ancillary single photon with a certain probability, while the conventional ECPs require two copies of partially entangled pairs at least. Our first protocol is implemented with linear optics and the second protocol is implemented with cross-Kerr-nonlinearities. Compared with other ECPs, they do not need to know the accurate coefficients of the initial state. With linear optics, it is feasible with current experiments. With cross-Kerr-nonlinearities, it does not require sophisticated single-photon detectors and can be repeated to get a higher success probability. Moreover, the second protocol can get the higher entanglement transformation efficiency and it may be the most economical protocol by far. Meanwhile, both protocols are more suitable for multiphoton system concentration because they need less operations and classical communications. All these advantages make the two protocols useful in current long-distance quantum communications.
An entangled coherent state (ECS) is one type of entanglement, which is widely discussed in the application of quantum information processing (QIP). In this paper, we propose an entanglement concentration protocol (ECP) to distill the maximally entangled W-type ECS from the partially entangled W-type ECS. In the ECP, we adopt the balanced beam splitter (BS) to make the parity check measurement. Our ECP is quite different from the conventional ECPs. After performing the ECP, not only can we obtain the maximally entangled ECS with some success probability, but also we can increase the amplitude of the coherent state. Therefore, it is especially useful in long-distance quantum communication, if the photon loss is considered.