Abstract
In 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. Here, we implement chiral quantum optics using a low-noise quantum dot in an open microcavity. 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. This is achieved by tuning the photon-emitter coupling in situ to the optimal operating condition (β = 0.5). Proof that the non-reciprocity arises from a single quantum emitter lies 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.
Highlights
In a non-chiral one-dimensional atom, an atom is coupled to a right-propagating and to a left-propagating mode in a singlemode waveguide
In the ideal limit, the atom acts as a perfect mirror: the reflectivity is R = 1; the transmission T = 01,2
The optical setup consists of a polarising beam-splitter and a quarter-wave plate set at 45∘ with respect to the polarising beam-splitter axes
Summary
In a non-chiral one-dimensional atom, an atom is coupled to a right-propagating and to a left-propagating mode in a singlemode waveguide. In the ideal limit (perfect atom with β = 1, where β is the probability that the excited atom emits a photon into the waveguide mode, a single photon at the input in resonance with the atom), the atom acts as a perfect mirror: the reflectivity is R = 1; the transmission T = 01,2. This changes completely in a chiral one-dimensional atom: R and T depend on the propagation direction, left-to-right (1 → 2) or rightto-left (2 → 1), i.e., the system exhibits non-reciprocity (T1→2 ≠ T2→1).
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