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Control of entanglement and two-qubit quantum gates with atoms crossing a detuned optical cavity

Gonta, D., Fritzsche, S.

Published Jan 1, 2009• 4 citations
OpenAlex

Abstract

A scheme is proposed to generate an entangled state between two (Λ-type) four-level atoms that interact effectively by means of a detuned optical cavity and a laser beam that acts perpendicularly to the cavity axis.It is shown how the degree of entanglement for two atoms passing through the cavity can be controlled by manipulating their velocity and the (initial) distance between the atoms.In addition, three realistic schemes are suggested to implement the two-qubit gates within the framework of the suggested atom-cavity-laser setup, namely, the i-swap gate, controlled-Z gate, and the controlled-NOT gate.For all these schemes, we analyze and discuss the atomic velocities and inter-atomic distances for which these gates are realized most reliably.

Related papers

Control of entanglement and two-qubit quantum gates with atoms crossing a detuned optical cavity

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A scheme is proposed to generate an entangled state between two (Lambda-type) four-level atoms that interact effectively by means of a detuned optical cavity and a laser beam that acts perpendicularly to the cavity axis. It is shown how the degree of entanglement for two atoms passing through the cavity can be controlled by manipulating their velocity and the (initial) distance between the atoms. In addition, three realistic schemes are suggested to implement the two-qubit gates within the framework of the suggested atom-cavity-laser setup, namely, the i-swap gate, controlled-Z gate and the controlled-NOT gate. For all these schemes, we analyze and discuss the atomic velocities and inter-atomic distances for which these gates are realized most reliably.

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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.

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Realization of Three-Qubit Controlled-Phase Gate Operation with Atoms in Cavity QED System

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Feasible schemes for quantum swap gates of optical qubits via cavity QED

Deng-Yu Zhang, Shi-Qing Tang, Xin-Wen Wang +2 more

Feasible schemes for implementing quantum swap gates of both coherent-state qubits and photonic qubits are proposed using a Λ-type atomic ensemble trapped in a bimodal optical cavity. In both protocols, the decoherence from atomic spontaneous emission is negligible due to the fact that the excited states of the atoms are adiabatically eliminated under large detuning condition and the swap gates can be created in a single step. In our schemes, the required atoms—cavity interaction time decreases with the increase of the number of atoms, which is very important in view of decoherence. The experimental feasibilities of the schemes are also discussed.

Chinese Physics B•Apr 1, 2011•4 citations
A scheme is proposed to generate an entangled state between two (Λ-type) four-level atoms that interact effectively by means of a detuned optical cavity and a laser beam that acts perpendicularly to the cavity axis.It is shown how the degree of entanglement for two atoms passing through the cavity can be controlled by manipulating their velocity and the (initial) distance between the atoms.In addition, three realistic schemes are suggested to implement the two-qubit gates within the framework of the suggested atom-cavity-laser setup, namely, the i-swap gate, controlled-Z gate, and the controlled-NOT gate.For all these schemes, we analyze and discuss the atomic velocities and inter-atomic distances for which these gates are realized most reliably.
A scheme is proposed to generate an entangled state between two (Lambda-type) four-level atoms that interact effectively by means of a detuned optical cavity and a laser beam that acts perpendicularly to the cavity axis. It is shown how the degree of entanglement for two atoms passing through the cavity can be controlled by manipulating their velocity and the (initial) distance between the atoms. In addition, three realistic schemes are suggested to implement the two-qubit gates within the framework of the suggested atom-cavity-laser setup, namely, the i-swap gate, controlled-Z gate and the controlled-NOT gate. For all these schemes, we analyze and discuss the atomic velocities and inter-atomic distances for which these gates are realized most reliably.
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 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.
Feasible schemes for implementing quantum swap gates of both coherent-state qubits and photonic qubits are proposed using a Λ-type atomic ensemble trapped in a bimodal optical cavity. In both protocols, the decoherence from atomic spontaneous emission is negligible due to the fact that the excited states of the atoms are adiabatically eliminated under large detuning condition and the swap gates can be created in a single step. In our schemes, the required atoms—cavity interaction time decreases with the increase of the number of atoms, which is very important in view of decoherence. The experimental feasibilities of the schemes are also discussed.