Directional amplification with a Josephson circuit

TL;DR

This paper demonstrates a chip-based non-reciprocal amplifier using coupled Josephson parametric converters that achieves directional signal amplification with low noise, tunability, and potential integration with quantum circuits.

Contribution

It introduces a Josephson circuit-based directional amplifier exploiting non-reciprocal phase response, controllable via microwave pump tones, with high gain, low noise, and on-chip integration potential.

Findings

Achieves 15 dB forward gain at 8.453 GHz

Provides 8 dB suppression of reflected signals

Adds less than 1.5 photons of noise at the signal frequency

Abstract

Non-reciprocal devices, which have different transmission coefficients for propagating waves in opposite directions, are crucial components in many low noise quantum measurements. In most schemes, magneto-optical effects provide the necessary non-reciprocity. In contrast, the proof-of-principle device presented here, consists of two on-chip coupled Josephson parametric converters (JPCs), which achieves directionality by exploiting the non-reciprocal phase response of the JPC in the trans-gain mode. The non-reciprocity of the device is controlled in-situ by varying the amplitude and phase difference of two independent microwave pump tones feeding the system. At the desired working point and for a signal frequency of 8.453 GHz, the device achieves a forward power gain of 15 dB within a dynamical bandwidth of 9 MHz, a reverse gain of -6 dB and suppression of the reflected signal by 8 dB. We also find that the amplifier adds a noise equivalent to less than one and a half photons at the signal frequency (referred to the input). It can process up to 3 photons at the signal frequency per inverse dynamical bandwidth. With a directional amplifier operating along the principles of this device, qubit and readout preamplifier could be integrated on the same chip.