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arXiv:0902.1372 · Physical Review A

Quantum-information processing with a single photon by an input-output process with respect to low- Q cavities

Jun‐Hong An, Mang Feng, C. H. Oh

Published Mar 4, 2009• 199 citations
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Abstract

Both cavity quantum electrodynamics and photons are promising candidates for quantum information processing. We consider a combination of both candidates with a single photon going through spatially separate cavities to entangle the atomic qubits, based on the input-output process of the cavities. We present a general expression for the input-output process regarding the low-$Q$ cavity confining a single atom, which works in a wide range of parameters. Focusing on low-$Q$ cavity case, we propose some schemes for quantum information processing with Faraday rotation using single photons, which is much different from the high-$Q$ cavity and strong-coupling cases.

DOI
10.1103/physreva.79.032303

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Both cavity quantum electrodynamics and photons are promising candidates for quantum information processing. We consider a combination of both candidates with a single photon going through spatially separate cavities to entangle the atomic qubits, based on the input-output process of the cavities. We present a general expression for the input-output process regarding the low-QQQ cavity confining a single atom, which works in a wide range of parameters. Focusing on low-QQQ cavity case, we propose some schemes for quantum information processing with Faraday rotation using single photons, which is much different from the high-QQQ cavity and strong-coupling cases.
We investigate the possibility to achieve quantum gates using atoms confined in low-QQQ cavities by single-photon input-output process. Different from in high-QQQ cavities with strong coupling, we may accomplish universal quantum gates on the atoms by Faraday rotations. Our idea could be applied to multiqubit gating on local and nonlocal atoms as well as on encoded qubits in decoherence-free subspace.
We consider the input-output process with low-QQQ cavities confining atoms for quantum-information processing, based on a general expression for reflection coefficient of the single photon. Focusing on the qubit encoding in decoherence-free subspace (DFS), we propose entanglement generation, universal quantum computing, and multiqubit controlled phase flip, using individual photon input and output from the cavities. Because of the DFS and no requirement for high-QQQ cavities, our schemes are not only immune to dephasing but also feasible with currently available technology.
Both cavity quantum electrodynamics and photons are promising candidates for quantum information processing. Here we present two efficient schemes for universal quantum gates, that is, Fredkin gates and SWAP gates on atomic systems, assisted by Faraday rotation catalyzed by an auxiliary single photon. These gates are achieved by successfully reflecting an auxiliary single photon from an optical cavity with a single-trapped atom. They do not require additional qubits and they only need some linear-optical elements besides the nonlinear interaction between the flying photon and the atoms in the optical cavities. Moreover, these two universal quantum gates are robust. A high fidelity can be achieved in our schemes with current experimental technology. They may be very useful in quantum information processing in future, with the great progress on controlling atomic systems.
Based on the input-output relation in low-Q cavities, we propose a feasible scheme to prepare remotely a single-atom state via photonic Faraday rotation, and then the scheme is generalized to the case of remote preparation of a two-atom entangled state. Our results show that when the coefficients of the initial atomic state to be prepared are real, both remote preparation of the single-atom state and that of the two-atom entangled state can be achieved deterministically by selecting appropriate parameters of the systems for the interactions among the atom, polarized single-photon pulse, and cavity field. Compared with the existing schemes for remote preparation of atomic states, in our scheme photons are used as flying qubits to transmit quantum information, which is suitable indeed to achieve a long-distance atomic state preparation in principle. Due to the fact that the information of atomic state is encoded in two degenerate ground-state levels of a -type three-level atom confined in a unilateral dissipative cavity, and that the atoms are only virtually excited, our schemes are insensitive to both cavity decay and atomic spontaneous emission. Besides, the two schemes we proposed do not need two- or multi-particle orthogonal measurements, only product-state measurements are involved, as well as they work in low-Q regime and do not require a strong coupling condition between the atoms and the optical cavities, which greatly reduce the experimental difficulty.
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.