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Journal of Modern Optics

Cavity-QED-based phase gate for photonic qubits

Yuli Dong, Xu‐Bo Zou, ShengLi Zhang, Song Yang, Chuan‐Feng Li, Guang‐Can Guo

Published Jun 20, 2009• 13 citations
Publisher

Abstract

We present a two-qubit phase gate for photonic qubits using a three-level atom trapped in an optical cavity. In the scheme, the two ground states are coupled to the excited state by two cavity fields, respectively, and one of them is driven by a classical laser field. It is shown that, based on the large-detuning condition, the decay of atomic spontaneous emission can be effectively suppressed. The influence of cavity decay on our scheme is also investigated.

DOI
10.1080/09500340903003339

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We propose a scheme for realization of three-qubit controlled-phase gate via passing two three-level atoms through a high-Q optical cavity in a cavity QED system. In the presented protocol, the two stable ground states of the atoms act as the two controlling qubits and the zero- and one-photon Fock states of the cavity-field form the target qubit, and no auxiliary state or any measurement is required. The numerical simulation shows that the gate fidelities remain at a high level under the influence of the atomic spontaneous emission, the decay of the cavity mode and deviation of the coupling strength. The experimental feasibility of our proposal is also discussed.
We propose a scheme for implementing a two-qubit quantum phase gate for intracavity fields. In the scheme, two qubits are encoded in zero- and one-photon Fock states of two intracavity modes, and a four-level N\mathsf{N}N-type atomic ensemble trapped in a cavity mediates the conditional phase gate within a given interaction time. We also discuss the influence of the atomic spontaneous emission and the decay of the cavity modes on the photon loss and gate fidelity, showing the scheme is within the current experiment technology.
A two-qubit quantum swap gate scheme based on coherent state qubit is proposed in cavity quantum electrodynamics system. Our scheme adopt the interaction between the Λ-type atomic ensemble and the two-mode optical cavity, and the swap gate can be realized directly only one step, so as to save a lot of quantum resources and reduce the number of single qubit rotation operations in the actual quantum information processing. It is found that under the condition of large detuning limit, the excited states of atoms are adiabatically eliminated, and the decoherence caused by the spontaneous emission of atoms is effectively suppressed. All atoms in the optical cavity are universally addressed, which reduces the experimental operation difficulty of the scheme. The fidelity of the quantum logic gate is maintained at a very high level when the photon loss of the cavity field is considered. Compared with the single-atom scheme, it is found that the atom-cavity interaction time required by the atomic ensemble scheme is inversely proportional to the number of atoms, so that the speed of the quantum logic gate can be increased by N times. Therefore, in principle, as long as enough atoms interacting with the optical field, an effective coupling of any atom-cavity field can be generated, which is conducive to selecting the appropriate quantum gate operation time in practical operation and effectively avoiding decoherence.
We describe a quantum phase gate in which the two qubits are represented by the photons in the two modes of the cavity field. The gate is implemented by passing a three-level atom in a cascade configuration through the cavity. The upper levels of the atom are resonant with one of the cavity modes whereas the lower levels are appropriately detuned from the other mode of the cavity. A $\ensuremath{\pi}$ phase shift is introduced when there is one photon each in the two modes and the atom is initially in the ground state. We also discuss the one-bit unitary gate in such a system and discuss potential applications.