Enhanced energy relaxation process of a quantum memory coupled to a superconducting qubit

Abstract

For quantum information processing, each physical system has a different advantage as regards implementation, so hybrid systems that benefit from the advantage of several systems would provide a promising approach. One common hybrid approach involves combining a superconducting qubit as a controllable qubit and another quantum system with a long coherence time as a memory qubit. The use of a superconducting qubit gives us excellent controllability of the quantum states, and the memory qubit is capable of storing information for a long time. It has been believed that selective coupling can be realized between a superconducting qubit and a memory qubit by tuning the energy splitting between them. However, we have shown that this detuning approach has a fundamental drawback as regards energy leakage from the memory qubit. Even if the superconducting qubit is effectively separated by reasonable detuning, a non-negligible incoherent energy relaxation in the memory qubit occurs via residual weak coupling when the superconducting qubit is affected by severe dephasing. This energy transport from the memory qubit to the control qubit can be interpreted as the appearance of the anti–quantum Zeno effect induced by the fluctuation in the superconducting qubit. We also discuss possible ways to avoid this energy relaxation process, which is feasible with existing technology.

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