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Communications in Theoretical Physics

Unconventional Geometric Phase-Shift Gates Based on Superconducting Quantum Interference Devices Coupled to a Single-Mode Cavity

Kehui Song, Zheng-Wei Zhou, Guo Guang-Can

Published Oct 1, 2006• 0 citations
Publisher

Abstract

We present a scheme to realize geometric phase-shift gate for two superconducting quantum interference device (SQUID) qubits coupled to a single-mode microwave field. The geometric phase-shift gate operation is performed in two lower flux states, and the excited state |2⟩ would not participate in the procedure. The SQUIDs undergo no transitions during the gate operation. Thus, the docoherence due to energy spontaneous emission based on the levels of SQUIDs are suppressed. The gate is insensitive to the cavity decay throughout the operation since the cavity mode is displaced along a circle in the phase space, acquiring a phase conditional upon the two lower flux states of the SQUID qubits, and the cavity mode is still in the original vacuum state. Based on the SQUID qubits interacting with the cavity mode, our proposed approach may open promising prospects for quantum logic in SQUID-system.

DOI
10.1088/0253-6102/46/4/014

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We propose a potential scheme for carrying out two-qubit unconventional geometric logic gates on two identical superconducting quantum-interference-device (SQUID) qubits coupled to a single-mode microwave field. The geometric logic gate operation is performed in two lower flux states, and the excited state |2 does not participate in the procedure. The SQUIDs undergo no transitions during gate operation. Thus, the decoherence due to energy spontaneous emission based on the levels of SQUIDs is suppressed. We present the two-qubit unconventional geometric logic gates in both an ideal cavity and a real cavity with decay. Discussions about the fidelity and the success probability of the proposed scheme as well as the experimental feasibility are given in detail.
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In the system with superconducting quantum interference devices (SQUID) in cavity,a scheme for con- structing two-qubit quantum phase gate via a conventional geometric phase-shift is proposed by using a quantized cavity field and classical microwave pulses.In this scheme,the gate operation is realized in the subspace spanned by the two lower flux states of the SQUID system and the population operator of the excited state has no effect on it.Thus the effect of decoherence caused from the levels of the SQUID system is possible to minimize.Under cavity decay,our strictly numerical simulation shows that it is also possible to realize the unconventional geometric phase gate.The experimental feasibility is discussed in detail.
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.
We propose a scheme for realizing two-qubit quantum phase gates via an unconventional geometric phase shift using two four-level superconducting artificial atoms with cyclic population transfer (broken symmetry) in a cavity. In this scheme, the logical gates' operation only involves the metastable states of each artificial atom. Moreover, under certain conditions, the atoms are disentangled with the cavity mode. Thus, the gate is insensitive to both the atomic spontaneous emission and the cavity decay.
Based on superconducting quantum interference devices (SQUID's) coupled to a cavity, we propose a scheme for implementing a quantum phase-shift gate and generating a WWW state by an adiabatic evolution of dark eigenstates, without any contributions from dynamical and geometric gates. The Sole requirement is of adiabatically increasing or decreasing Rabi frequencies of classical microwave pluses. Thus, the manipulation is robust against certain types of errors. We also analyze the experimental possibility that identical coupling can be achieved between SQUID qubits and cavity fields, and the cavity decay can be ignored in certain conditions. Based on a simple operation, our scheme may be realized in this solid-state system.