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# Near-quantum-limited amplification from inelastic Cooper-pair tunnelling

## Abstract

The readout of microwave quantum systems, such as spin or superconducting qubits, requires low-noise amplifiers with added noise as close as possible to the quantum limit. This limit has so far been approached only by parametric amplifiers that exploit nonlinearities in superconducting circuits and are driven by a strong microwave pump tone. However, this microwave drive makes the amplifiers much more difficult to implement and operate than conventional d.c.-powered amplifiers, which currently suffer from much higher noise. Here, we show that a simple d.c.-powered set-up can provide amplification close to the quantum limit. Our amplification scheme is based on the stimulated microwave photon emission accompanying inelastic Cooper-pair tunnelling through a d.c.-biased Josephson junction. The key to the low noise of this approach is a well-defined auxiliary idler mode, which allows for operation analogous to parametric amplifiers.

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## Acknowledgements

The authors acknowledge discussions with J. Leppäkangas, C. Altimiras, M. Devoret, B. Kubala and J. Ankerhold, as well as financial support from the Grenoble Nanosciences Foundation (grant WiQOJo), the European Union (ERC starting grant 278203 WiQOJo and ICT grant 218783 SCoPE) and the ANR (grants Masquelspec, AnPhoTEQ, JosePhSCharLi).

## Author information

Authors

### Contributions

S.J., F.B. and A.G. performed the measurements and analysed the data. M.H., F.P. and D.V. designed and fabricated the sample. A.G., M.H., F.B., R.A., S.J. and D.H. built the set-up and wrote software. M.H. and S.J. wrote the manuscript with input from all authors.

### Corresponding author

Correspondence to M. Hofheinz.

## Ethics declarations

### Competing interests

The authors declare no competing interests.

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## Supplementary information

### Supplementary Information

Supplementary Note 1, Supplementary Figures 1–2

## Rights and permissions

Reprints and Permissions

Jebari, S., Blanchet, F., Grimm, A. et al. Near-quantum-limited amplification from inelastic Cooper-pair tunnelling. Nat Electron 1, 223–227 (2018). https://doi.org/10.1038/s41928-018-0055-7

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• DOI: https://doi.org/10.1038/s41928-018-0055-7

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