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Physical Review A

Quantum gate operations in the decoherence-free subspace of superconducting quantum-interference devices

Chunfeng Wu, Xun‐Li Feng, X. X. Yi, Isabel Meiqi Chen, C. H. Oh

Published Dec 11, 2008• 23 citations
Publisher

Abstract

We propose a scheme for implementing single-qubit and nontrivial two-qubit gate operations in a system with superconducting quantum interference devices (SQUIDs) via Raman transitions in circuit QED. The gate operations only involve the two lower flux states of the SQUID, and hence the effect of the excited state can be neglected. By encoding quantum information into the decoherence free subspace of the SQUID system, the evolution of the system results in fault-tolerant quantum gates. The effect of decoherence caused by the decay of the transmission line resonator is investigated.

DOI
10.1103/physreva.78.062321

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We propose a scheme for implementing single-qubit and nontrivial two-qubit gate operations in a system with superconducting quantum interference devices (SQUIDs) via Raman transitions in circuit QED. The gate operations only involve the two lower flux states of the SQUID, and hence the effect of the excited state can be neglected. By encoding quantum information into the decoherence free subspace of the SQUID system, the evolution of the system results in fault-tolerant quantum gates. The effect of decoherence caused by the decay of the transmission line resonator is investigated.
We put forward a simple scheme for one-step realization of a two-qubit SWAP gate with SQUIDs (super-conducting quantum-interference devices) in cavity QED via Raman transition. In this scheme, the cavity field is only virtually excited and thus the cavity decay is suppressed. The SWAP gate is realized by using only two lower flux states of the SQUID system and the excited state would not be excited. Therefore, the effect of decoherence caused from the levels of the SQUID system is possibly minimized. The scheme can also be used to implement the SWAP gate with atoms.
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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.