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Chinese Journal of Quantum Electronics

Realization of two-atom quantum controlled phase gate with high efficiency via cavity QED

SU Xiao-qin

Published Jan 1, 2006• 0 citations
OpenAlex

Abstract

Any quantum computation can be simplified to a gate sequence. But the quantum computation is carried out by a certain physical system. We propose here a scheme to carry out two-atom quantum controlled phase gate through cavity QED. In our scheme, the atomic transition is largely detuned with the cavity mode of interest, so the atomic spontaneous emission loss is strongly suppressed, and this leads to the enhancement of probability of gate operation. But fidelity is decided by constantsα,β,γ. The numerical calculation based on current experimental technology shows that our scheme has high gate fidelity, the average value of fidelity F = 0.982318. That scheme can be realized by experiment.

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Any quantum computation can be simplified to a gate sequence. But the quantum computation is carried out by a certain physical system. We propose here a scheme to carry out two-atom quantum controlled phase gate through cavity QED. In our scheme, the atomic transition is largely detuned with the cavity mode of interest, so the atomic spontaneous emission loss is strongly suppressed, and this leads to the enhancement of probability of gate operation. But fidelity is decided by constantsα,β,γ. The numerical calculation based on current experimental technology shows that our scheme has high gate fidelity, the average value of fidelity F = 0.982318. That scheme can be realized by experiment.
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 the implementation of the quantum-controlled phase gate between distant atoms. Two special lasers adiabatically drive an atom trapped in a cavity that unidirectionally couples to the other cavity trapping an atom; then the phase gate between the two atoms is realized by introduction of measurement and local operations. The numerical simulations show that the quality factor of the gate operation is close to unity even if the atomic spontaneous emission is taken into account; the success probability approaches unity in principle.
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.
A scheme is proposed to realize a two-qubit quantum phase gate for the intracavity modes. In the scheme, two qubits are encoded in zero- and one-photon Fock states of two intracavity modes, and the three-level $\ensuremath{\Lambda}$-type atom trapped in a high-QQQ cavity mediates the conditional phase gate within a given interaction time. The influence of cavity decay and atomic spontaneous emission on the gate fidelity is also discussed.
We propose a scheme for realizing two-qubit quantum phase gates via an unconventional geometric phase shift with atoms in a cavity. In the scheme the atoms interact simultaneously with a highly detuned cavity mode and a classical field. The atoms undergo no transitions during the gate operation, while the cavity mode is displaced along a circle in the phase space, aquiring a geometric phase conditional upon the atomic state. Under certain conditions, the atoms are disentangled with the cavity mode and thus the gate is insensitive to both the atomic spontaneous emission and the cavity decay.