Microwave Measurement beyond the Quantum Limit with a Nonreciprocal Amplifier

F. Lecocq, L. Ranzani, G. A. Peterson, K. Cicak, A. Metelmann, S. Kotler, R. W. Simmonds, J. D. Teufel, J. Aumentado

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


The measurement of a quantum system is often performed by encoding its state in a single observable of a light field. The measurement efficiency of this observable can be reduced by loss or excess noise on the way to the detector. Even a quantum-limited detector that simultaneously measures a second noncommuting observable would double the output noise, therefore limiting the efficiency to 50%. At microwave frequencies, an ideal measurement efficiency can be achieved by noiselessly amplifying the information-carrying quadrature of the light field but this has remained an experimental challenge. Indeed, while state-of-the-art Josephson-junction-based parametric amplifiers can perform an ideal single-quadrature measurement, they require lossy ferrite circulators in the signal path, drastically decreasing the overall efficiency. In this paper, we present a nonreciprocal parametric amplifier that combines single-quadrature measurement and directionality without the use of strong external magnetic fields. We extract a measurement efficiency of 62-9+17% that exceeds the quantum limit and that is not limited by fundamental factors. The amplifier can be readily integrated with superconducting devices, creating a path for ideal measurements of quantum bits and mechanical oscillators.

Original languageAmerican English
Article number044005
JournalPhysical Review Applied
Issue number4
StatePublished - Apr 2020
Externally publishedYes

Bibliographical note

Funding Information:
This work was supported by the NIST Quantum Information Program. Contributions to this paper by workers at NIST, an agency of the U.S. Government, are not subject to U.S. copyright.

Publisher Copyright:
© 2020 American Physical Society. © 2020 American Physical Society. US.


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