Widely tunable, non-degenerate three-wave mixing microwave device operating near the quantum limit

TL;DR

This paper reports the first experimental realization of a widely tunable, non-degenerate three-wave mixing device operating near the quantum limit, based on a novel superconducting Josephson junction ring with flux control.

Contribution

It introduces a new superconducting device with a unique phase configuration that allows wide frequency tunability and low noise operation for quantum microwave signals.

Findings

Device operates as a low-noise, tunable amplifier.

Achieved precise measurement of zero-point-fluctuations and shot noise crossover.

Provides an upper bound on intrinsic noise and dissipation.

Abstract

We present the first experimental realization of a widely frequency tunable, non-degenerate three-wave mixing device for quantum signals at GHz frequency. It is based on a new superconducting building-block consisting of a ring of four Josephson junctions shunted by a cross of four linear inductances. The phase configuration of the ring remains unique over a wide range of magnetic fluxes threading the loop. It is thus possible to vary the inductance of the ring with flux while retaining a strong, dissipation-free, and noiseless non-linearity. The device has been operated in amplifier mode and its noise performance has been evaluated by using the noise spectrum emitted by a voltage biased tunnel junction at finite frequency as a test signal. The unprecedented accuracy with which the crossover between zero-point-fluctuations and shot noise has been measured provides an upper-bound for the noise and dissipation intrinsic to the device.