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Analog information processing at the quantum limit with a Josephson ring modulator


Amplifiers are crucial in every experiment carrying out a very sensitive measurement. However, they always degrade the information by adding noise. Quantum mechanics puts a limit on how small this degradation can be. Theoretically, the minimum noise energy added by a phase-preserving amplifier to the signal it processes amounts at least to half a photon at the signal frequency. Here we propose a practical microwave device that can fulfil the minimal requirements to reach the quantum limit. The availability of such a device is of importance for the readout of solid-state qubits, and more generally for the measurement of very weak signals in various areas of science. We discuss how this device can be the basic building block for a variety of practical applications, such as amplification, noiseless frequency conversion, dynamic cooling and production of entangled signal pairs.

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Figure 1: Electrical modes and energy states of the Josephson ring modulator.
Figure 2: Description of the Josephson parametric converter.
Figure 3: Gain of the JPC.
Figure 4: Main constraint on the gain × bandwidth product of the JPC.


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This work was supported by NSA through ARO grant number W911NF-05-01-0365, the Keck foundation and the NSF through grant number DMR-032-5580. M.H.D. acknowledges partial support from College de France. We are indebted to B. Abdo for help with the proof corrections.

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Authors and Affiliations



M.H.D. proposed the original idea of the ring modulator. N.B. and M.H.D. developed the device, carried out the theoretical analysis and wrote the article. R.V., V.E.M. and I.S. contributed extensively to discussions of the results. S.M.G. introduced all authors to the multifunctional aspect of three-wave mixing. R.J.S. contributed by his knowledge of ultralow-noise microwave circuits and measurements.

Corresponding authors

Correspondence to N. Bergeal or M. H. Devoret.

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The authors declare no competing financial interests.

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Bergeal, N., Vijay, R., Manucharyan, V. et al. Analog information processing at the quantum limit with a Josephson ring modulator. Nature Phys 6, 296–302 (2010).

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