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arXiv:cond-mat/0312696 · Physical Review B

Reading out the state inductively and microwave spectroscopy of an interferometer-type charge qubit

Detlef Born, V. I. Shnyrkov, Wolfram Krech, Th. Wagner, E. V. Il’ichev, M. Grajcar, Uwe Hübner, H.‐G. Meyer

Published Nov 9, 2004• 40 citations
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Abstract

We implemented experimentally an interferometer-type charge qubit consisting of a single-Cooper-pair transistor closed by a superconducting loop that is in flip-chip configuration inductively coupled to a radio-frequency tank circuit. The tank permits us to readout the qubit state, acting as an inductance measuring apparatus. By applying continuous microwave power to the quantum device, we observed inductance alterations caused by redistributions of the energy-level populations. From the measured data we extracted the energy gap between ground and upper levels as a function of the transistor quasicharge as well as the Josephson phase across both junctions.

DOI
10.1103/physrevb.70.180501

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We use the density matrix formalism to analyze the interaction of interferometer-type superconducting qubits with a high quality tank circuit, which frequency is well below the gap frequency of a qubit. We start with the ground state characterization of the superconducting flux and charge qubits. Then, by making use of a dressed state approach, we describe the qubits' spectroscopy when the qubit is irradiated by a microwave field which is tuned to the gap frequency. The last section of the paper is devoted to continuous monitoring of qubit states by using a dc superconducting quantum interference device in the inductive mode.