A single-photon optical diode operates on individual photons and allows unidirectional propagation of photons. By exploiting the unique polarization configuration in a waveguide, we show here that a single-photon optical diode can be accomplished by coupling a quantum impurity to a passive, linear optical waveguide which possesses a locally planar, circular polarization. We further show that the diode provides a near unitary contrast for an input pulse with finite frequency bandwidth and can be implemented in a variety of types of waveguides. Moreover, the performance of the diode is not sensitive to the intrinsic dissipation of the quantum impurity.
"During the last decade experiments have succeeded in coupling single quantum emitters to 1D systems , in a variety of well-established technologies, such as superconducting circuits, semiconductor quantum dots, and nitrogen vacancy centers in diamonds    . Likewise , theoretical studies have been directed toward conceiving basic optoelectronic devices that are able to work at the single-or few-photon level, such as quantum optical diodes     . "
[Show abstract][Hide abstract] ABSTRACT: Unidirectional light transport in one-dimensional nanomaterials at the
quantum level is a crucial goal to achieve for upcoming computational devices.
We here employ a full-quantum mechanical approach based on master equation to
describe unidirectional light transport through a pair of two-level systems
coupled to a one-dimensional waveguide. By comparing with published
semi-classical results, we find that the nonlinearity of the system is reduced,
thereby reducing also the unidirectional light transport efficiency. Albeit not
fully efficient, we find that the considered quantum system can work as a light
diode with an efficiency of approximately 60%. Our results may be used in
quantum computation with classical and quantized light.
"This can be exploited to create non-reciprocal transmission at certain frequencies in the waveguide by having the cavity interact with a system sensitive to the helicity of the electric field. As in  and , we consider a V-type three-level system consisting of a ground state, |g, and two excited states, |e 1 and |e 2 with transitions to each excited state driven by opposite electric field helicity (Fig. 3b). Such a system could be realized by a quantum dot with a Zeeman-like splitting (Sec. "
[Show abstract][Hide abstract] ABSTRACT: We describe an approach to optical non-reciprocity that exploits the local
helicity of evanescent electric fields in axisymmetric resonators. By
interfacing an optical cavity to helicity-sensitive transitions, such as Zeeman
levels in a quantum dot, light transmission through a waveguide becomes
direction-dependent when the state degeneracy is lifted. Using a linearized
quantum master equation, we analyze the configurations that exhibit
non-reciprocity, and we show that reasonable parameters from existing cavity
QED experiments are sufficient to demonstrate a coherent non-reciprocal optical
isolator operating at the level of a single photon.
"Furthermore, the access to photon nonlinearities that are sensitive at the SP level   would open for novel opportunities of constructing highly efficient deterministic quantum gates       . A single quantum emitter that is efficiently coupled to a photonic waveguide  would facilitate such a SP nonlinearity, enabling the realization of single-photon switches and diodes   , as well as serve as a highly efficient single-photon source. So far, experimental progress has been limited to superconducting qubit systems where the generation of nonclassical states at microwave frequencies was reported . "
[Show abstract][Hide abstract] ABSTRACT: A quantum emitter efficiently coupled to a nanophotonic waveguide constitutes
a promising system for the realization of single-photon transistors,
quantum-logic gates based on giant single-photon nonlinearities, and high
bit-rate deterministic single-photon sources. The key figure of merit for such
devices is the beta-factor, which is the probability for an emitted single
photon to be channeled into a desired waveguide mode. Here we report on the
experimental achievement of beta = 98.43 +- 0.04% for a quantum dot coupled to
a photonic-crystal waveguide. This constitutes a nearly ideal photon-matter
interface where the quantum dot acts effectively as a 1D "artificial" atom
since it interacts almost exclusively with just a single propagating optical
mode. The beta-factor is found to be remarkably robust to variations in
position and emission wavelength of the quantum dots. Our work demonstrates the
extraordinary potential of photonic-crystal waveguides for highly efficient
single-photon generation and on-chip photon-photon interaction.
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