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Journal of the Optical Society of America B

Atomic quantum information processing in low-Q cavity in the intermediate coupling region

Shi‐Lei Su, Qi Guo, Long Zhu, Hong‐Fu Wang, Shou Zhang

Published Sep 19, 2012• 10 citations
Publisher

Abstract

We present an atomic-state entangler with single atoms trapped in separated low-Q cavities, a coherent optical pulse as a quantum channel, a photon detector that only distinguishes the vacuum and nonvacuum states, and basic optical elements based on the input–output process in the intermediate coupling region with a higher probability and fidelity. The atomic-state entangler is meaningful because it does not need a strong coupling cavity and a single-photon source and could be feasible for large-scale quantum computation and quantum communication in the future. Based on this entangler, quantum information nonlocal transfer without classical communication, the quantum controlled-NOT gate, the four-particle |χ〉 state, the N-particle Greenberger-Horne-Zeilinger (GHZ) state, and cluster-state generation can be realized completely, which is useful in large-scale and nonlocal quantum information processing.

DOI
10.1364/josab.29.002827

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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.
We present a physical scheme to teleport an unknown atomic entangled state via cavity decay. In the teleportation process, four-particle Greenberger–Horne–Zeilinger (GHZ) state is used as quantum channel, and two unknown entangled atoms and two of four atoms in the four-particle GHZ state are trapped in four leaky cavities, respectively. Based on the joint detection of the photons leak out from the four cavities, we can teleport an unknown entangled state to two other remote atoms with certain probability and high fidelity.
We propose schemes to prepare n-atom Greenberger–Horne–Zeilinger (GHZ) state via two-sided cavities interacting with single-photon pulses, and achieve quantum state transfer (QST) from one atom to another atom. Entanglement particle pair and the control of coupling between qubits are of no need in the QST process. Some practical quantum noises only decrease the success probabilities of the schemes but have no influence on the fidelity of prepared state. In addition, the success probabilities of our schemes are close to unity in the ideal case.