Ultimate on-chip quantum amplifier

TL;DR

This paper demonstrates a fundamental quantum amplifier using a superconducting artificial atom, highlighting its gain limitations and noise performance dictated by spontaneous emission in an open 1D space.

Contribution

It introduces the first on-chip quantum amplifier based on a three-level superconducting circuit coupled to a transmission line.

Findings

Achieved amplification of electromagnetic waves with a superconducting quantum circuit.

Characterized the noise performance and gain limitations due to spontaneous emission.

Presented the system as the most fundamental quantum amplifier with intrinsic quantum noise.

Abstract

We report amplification of electromagnetic waves by a single artificial atom in open 1D space. Our three-level artificial atom -- a superconducting quantum circuit -- coupled to a transmission line presents an analog of a natural atom in open space. The system is the most fundamental quantum amplifier whose gain is limited by a spontaneous emission mechanism. The noise performance is determined by the quantum noise revealed in the spectrum of spontaneous emission, also characterized in our experiments.