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Efficient readout of flux qubits at degeneracy

A. Kack·F. K. Wilhelm
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Abstract

We present a superconducting circuit consisting of a flux qubit and a single-charge transistor serving as a detector. As flux and charge are conjugate, the transistor can detect states of the qubit close to the flux degeneracy point, when the eigenstates are quantum superpositions of fluxes. The coupling has a flip-flop symmetry conserving the total number of excitations, and so the measurement outcome results in the absence or presence of an incoherent tunneling cycle. We evaluate the performance of a practical device and show that it is an attractive tool for measuring at the degeneracy point.

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A. Kack, F. K. Wilhelm. 2005-05-21. Efficient readout of flux qubits at degeneracy. https://arxiv.org/abs/cond-mat/0505537

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