Single-photon frequency conversion via a giant $\Lambda$-type atom

TL;DR

This paper investigates how a giant $ ext{Lambda}$-type atom coupled at two points in a waveguide can enable phase-dependent elastic and inelastic single-photon scattering, leading to efficient, tunable frequency conversion.

Contribution

It introduces a model of a giant $ ext{Lambda}$-type atom with phase-dependent interference effects for frequency conversion, combining it with Sagnac interferometry for enhanced control.

Findings

Phase-dependent interference modifies decay rates and transition frequencies.

Optimal frequency conversion condition is phase-dependent.

Combining giant-atom interference with Sagnac interferometry achieves near-unit efficiency.

Abstract

We study single-photon scattering via a giant $\Lambda$-type atom, where both atomic transitions are coupled with the modes of a single waveguide at two separated points. The giant-atom structure introduces phase-dependent interference effects to both elastic (frequency-preserving) and inelastic (frequency-converting) scattering processes, which modify the corresponding decay rates (as well as the transition frequencies) such that the giant atom is capable of accessing the various limits of a small one. The condition of the optimal frequency conversion is also identified and shown to be phase dependent. Moreover, we consider the combination of the giant-atom interference and the Sagnac quantum interference by further inserting a Sagnac interferometer at each of the coupling points. It is shown that the two kinds of interference effects are compatible and play independent roles, such that efficient frequency conversion with unit efficiency can be achieved in addition to the phase-dependent phenomena induced by the giant-atom structure.