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Fast quantum limited read-out of a superconducting qubit using a slow oscillator

G. Johansson·L. Tornberg·C. M. Wilson
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Abstract

We describe how to perform fast quantum limited read-out of a solid state qubit biased at its degeneracy point. The method is based on homodyne detection of the phase of a microwave signal reflected by a slow oscillator coupled to the qubit. Analyzing the whole quantum read-out process, we find that the detection is indeed quantum limited and that this limit may be reached even using a resonance circuit with a low quality factor, thus enabling the use of short measurement pulses. As an example, we discuss in detail the read-out of a Cooper-pair box capacitively coupled to a lumped element LC-oscillator. Furthermore, we give formulas for the backaction while not measuring, and discuss optimal parameters for a realistic design capable of fast (~50 ns) single-shot read-out.

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G. Johansson, L. Tornberg, C. M. Wilson. 2006-10-26. Fast quantum limited read-out of a superconducting qubit using a slow oscillator. https://doi.org/10.1103/physrevb.74.100504

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