DC-powered broadband quantum-limited microwave amplifier

TL;DR

This paper introduces a novel DC-powered broadband quantum-limited microwave amplifier, the ICTA, which simplifies hardware and maintains near-quantum-limited noise performance for superconducting qubit readout.

Contribution

The first DC-powered broadband amplifier operating close to the quantum limit, eliminating the need for a pump tone and reducing hardware complexity.

Findings

Achieves 13 dB gain over 3.5 GHz bandwidth in a single stage

Operates within 0.2 photons of the quantum limit

Semiclassical simulations match experimental results

Abstract

Fast, high-fidelity, single-shot readout of superconducting qubits in quantum processors demands quantum-limited amplifiers to preserve the optimal signal-to-noise ratio. Typically, quantum-limited amplification is achieved with parametric down-conversion of a strong pump tone, which imposes significant hardware overhead and severely limits scalability. Here, we demonstrate the first DC-powered broadband amplifier operating within 0.2 photons of the quantum limit. Our impedance-engineered Inelastic Cooper-pair Tunneling Amplifier (ICTA)-a voltage-biased SQUID in which Cooper pairs tunnel inelastically by emitting signal-idler photon pairs-operates in reflection, delivering 13 dB of average gain across a 3.5 GHz bandwidth in a single stage. Semiclassical simulations accurately predict the gain and saturation power, enabling further design improvements. By eliminating the pump-tone infrastructure, the broadband ICTA promises to dramatically reduce the hardware complexity of quantum-limited amplification in superconducting quantum processors.