A chiral one-dimensional atom using a quantum dot in an open microcavity

TL;DR

This paper demonstrates a chiral quantum optical device using a quantum dot in an open microcavity, achieving non-reciprocal single-photon transmission with high contrast, enabling advanced quantum information processing applications.

Contribution

It introduces a novel implementation of chiral quantum optics with a quantum dot in an open microcavity, showing non-reciprocal photon transmission at the single-photon level.

Findings

Achieved non-reciprocal transmission ratio up to 10.7 dB.

Demonstrated nonlinearity and photon statistics consistent with single-emitter behavior.

Showed potential for single-photon phase shifters and quantum gates.

Abstract

In nanostructures, the light-matter interaction can be engineered to be chiral. In the fully quantum regime, a chiral one-dimensional atom, a photon propagating in one direction interacts with the atom; a photon propagating in the other direction does not. Chiral quantum optics has applications in creating nanoscopic single-photon routers, circulators, phase-shifters and two-photon gates. Furthermore, the directional photon-exchange between many emitters in a chiral system may enable the creation of highly exotic quantum states. Here, we present a new way of implementing chiral quantum optics $-$ we use a low-noise quantum dot in an open microcavity. Specifically, we demonstrate the non-reciprocal absorption of single photons, a single-photon diode. The non-reciprocity, the ratio of the transmission in the forward-direction to the transmission in the reverse direction, is as high as 10.7 dB, and is optimised $\textit{in situ}$ by tuning the photon-emitter coupling to the optimal operating condition ($\beta = 0.5$). Proof that the non-reciprocity arises from a single quantum emitter lies in the nonlinearity with increasing input laser power, and in the photon statistics $-$ ultralow-power laser light propagating in the diode's reverse direction results in a highly bunched output ($g^{(2)}(0) = 101$), showing that the single-photon component is largely removed. The results pave the way to a single-photon phase shifter, and, by exploiting a quantum dot spin, to two-photon gates and quantum non-demolition single-photon detectors.