Proposal for a continuous wave laser with linewidth well below the standard quantum limit

TL;DR

This paper proposes a superconducting circuit design for a microwave laser that can achieve linewidths below the standard quantum limit by engineering the coupling mechanisms to minimize quantum noise.

Contribution

It introduces a novel superconducting circuit design with engineered couplings that theoretically surpass the standard quantum limit for laser linewidths.

Findings

Theoretical analysis shows linewidth reduction below quantum limit

Design uses Josephson junctions, capacitors, and inductors

Proposes low-noise couplers for improved coherence

Abstract

Due to their high coherence, a laser is a ubiquitous tool in science. We show that by engineering the coupling between the gain medium and the laser cavity as well as the laser cavity and the output port, it is possible to eliminate most of the noise due to photons entering as well as leaving the laser cavity. Hence, it is possible to reduce the laser linewidth by a factor equal to the number of photons in the laser cavity below the standard quantum limit. We design and theoretically analyze a superconducting circuit that uses Josephson junctions, capacitors and inductors to implement a microwave laser, including the low-noise couplers that allow the design to surpass the standard quantum limit. Our proposal relies on the elements of superconducting quantum information, and thus is an example of how quantum engineering techniques can inspire us to re-imagine the limits of conventional quantum systems.