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

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.

4 pages,2 figures, Corrected typos and added contents. Accepted to Phys. Rev. B(R)

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• Dephasing of solid-state qubits at optimal points
• Nondestructive readout for a superconducting flux qubit
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Cited by in corpus (4)

• Coherence times of dressed states of a superconducting qubit under extreme driving
• Selective coupling of superconducting qubits via tunable stripline cavity
• Quantum detection of electronic flying qubits
• Time-Resolved Measurement of a Charge Qubit