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Communications in Theoretical Physics

Controlled Phase Flip Gate and Its Application in Low-Q Cavities by Single-Photon Input-Output Process

Bo Wang, Qiong Chen, Wan-Li Yang, Su-Peng Kou

Published Aug 1, 2012• 1 citation
Publisher

Abstract

By employing an auxiliary cavity, we investigate the possibility to implement the conditional phase flip (CPF) gate on two atoms confined in separate low-Q cavities by single-photon input-output process, based on the Faraday rotation. This indicates a universal quantum computing available with sophisticated cavity QED techniques. As examples, we carry out generation of cluster states of distant atomic qubits and accomplish a teleportation based on Bell-state measurement in low-Q cavities.

DOI
10.1088/0253-6102/58/2/10

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By employing an auxiliary cavity, we investigate the possibility to implement the conditional phase flip (CPF) gate on two atoms confined in separate low-Q cavities by single-photon input-output process, based on the Faraday rotation. This indicates a universal quantum computing available with sophisticated cavity QED techniques. As examples, we carry out generation of cluster states of distant atomic qubits and accomplish a teleportation based on Bell-state measurement in low-Q cavities.
We propose a basic scheme to construct a hybrid controlled phase-flip (CPF) gate between a flying pulse qubit and a stationary atomic qubit, assisted by a cavity input–output process for a low-Q cavity in the atom–cavity intermediate coupling region. The qubits can be encoded on the coherent states and ground states of the single-trapped L-level atom, respectively. We present a theoretical model of the hybrid CPF gate, whose basic strategy is to control the reflectivity of the input coherent optical pulse to obtain a phase shift conditioned by the different internal atomic states by adjusting the parameters of the cavity quantum electrodynamics (CQED) system. The resulting basic scheme can be used to construct nonlocal gates between remote atomic qubits confined in spatially separated cavities, and also for the generation of an atomic cluster state. The performance and experimental feasibilities of the proposed scheme indicate that it is robust against practical noise and feasible with current technologies. Thus, our scheme is applicable for use in large-scale quantum computation.
Quantum controlled-phase-flip (CPF) gate between a flying photon qubit and a stationary atomic qubit could allow the linking of distant computational nodes in a quantum network. Here we present a scheme to realize quantum CPF gate between a flying optical photon and an atomic ensemble based on cavity input-output process and Rydberg blockade. When a flying single-photon pulse is reflected off the cavity containing a Rydberg atomic ensemble, the dark resonance and Rydberg blockade induce a conditional phase shift for the photon pulse, thus we can achieve the CPF gate between the photon and the atomic ensemble. Assisted by Rydberg blockade interaction, our scheme works in the N-atoms strong-coupling regime and significantly relaxes the requirement of strong coupling of single atom to photon in the optical cavity.
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.
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Cavity quantum electrodynamics (cQED) enables deterministic controlled gates between neutral atom and photon qubits, such as the controlled phase flip (CPF) gate [1] , which is a key component for implementing quantum computation. The gate fidelity drops sharply when the length of an input-photon pulse is shorter than the inverse of the bandwidth of a cavity, because of the distortion of the output pulse. This limits the operational speed of the gates. One way to boost the limit of gate speed may be to reduce cavity length, since this increases the bandwidth of the cavity with keeping high cooperativity [2] .