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.
"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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