Phase-sensitive cascade quantum amplifier with nearly noiseless operation

Abstract

Phase-sensitive parametric devices enable quadrature-selective amplification with the potential for sub-quantum-limited noise performance. In this work, we investigate the operation of a SQUID-based Josephson Parametric Amplifier (JPA), comparing its performance in the phase-preserving and phase-sensitive regimes. The device, fabricated using VTT SWAPS technology, is driven in a three-wave mixing configuration and characterized in a reflection-based measurement setup at millikelvin temperatures. To directly probe the noise performance at low JPA gains, we employ a cascaded amplification scheme in which a Traveling-Wave Parametric Amplifier (TWPA) provides low-noise pre-amplification of the JPA output. In a phase-preserving operation, the JPA exhibits near-quantum-limited performance with a system noise temperature of $351\pm53$ mK at 6 GHz. In contrast, phase-sensitive operation yields a minimum system noise temperature of $94\pm12$ mK, well below the standard quantum limit of 288 mK. Our results demonstrate that a JPA-TWPA amplifier cascade opens the door to direct, high-fidelity probing of quantum devices without the need for background noise subtraction.