Efficient qubit measurement with a nonreciprocal microwave amplifier

Published

January 13, 2021

Author(s)

Florent Lecocq, Leonardo Ranzani, Gabriel A. Peterson, Katarina Cicak, Xiaoyue Jin, Raymond Simmonds, John Teufel, Jose Aumentado

Abstract

The act of observing a quantum object fundamentally perturbs its state, resulting in a random walk toward an eigenstate of the measurement operator. Ideally, the measurement is responsible for all dephasing of the quantum state. In practice, imperfections in the measurement apparatus limit or corrupt the flow of information required for quantum feedback protocols, an effect quantified by the measurement efficiency. Here we demonstrate the efficient measurement of a superconducting qubit using a nonreciprocal parametric amplifier to directly monitor the microwave field of a readout cavity. By mitigating the losses between the cavity and the amplifier we achieve a measurement efficiency of 72%. The directionality of the amplifier protects the readout cavity and qubit from excess backaction caused by amplified vacuum fluctuations. In addition to providing tools for further improving the fidelity of strong projective measurement, this work creates a testbed for the experimental study of ideal weak measurements, and it opens the way towards quantum feedback protocols based on weak measurement such as state stabilization or error correction.

Citation

Physical Review Letters

Pub Type

Journals

Citation

Lecocq, F. , Ranzani, L. , Peterson, G. , Cicak, K. , Jin, X. , Simmonds, R. , Teufel, J. and Aumentado, J. (2021), Efficient qubit measurement with a nonreciprocal microwave amplifier, Physical Review Letters (Accessed March 7, 2026)