Single-photon electroluminescence for on-chip quantum networks

An electrically driven single-photon source has been monolithically integrated with nano-photonic circuitry. Electroluminescent emission from a single InAs/GaAs quantum dot (QD) is channelled through a suspended nanobeam waveguide. The emission line has a linewidth of below 6 μeV, demonstrating the ability to have a high coherence, electrically driven, waveguide coupled QD source. The single-photon nature of the emission is verified by g(2) (τ) correlation measurements. Moreover, in a cross-correlation experiment, with emission collected from the two ends of the waveguide, the emission and propagation of single photons from the same QD is confirmed. This work provides the basis for the development of electrically driven on-chip single-photon sources, which can be readily coupled to waveguide filters, directional couplers, phase shifters, and other elements of quantum photonic networks

Shot noise of coupled semiconductor quantum dots

The low-frequency shot noise properties of two electrostatically coupled semiconductor quantum dot states which are connected to emitter/collector contacts are studied. A master equation approach is used to analyze the bias voltage dependence of the Fano factor as a measure of temporal correlations in tunneling current caused by Pauli's exclusion principle and the Coulomb interaction. In particular, the influence of the Coulomb interaction on the shot noise behavior is discussed in detail and predictions for future experiments will be given. Furthermore, we propose a mechanism for negative differential conductance and investigate the related super-Poissonian shot noise.Comment: submitted to PR

Magnetic field dependence of the exciton energy in a quantum disk

The groundstate energy and binding energy of an exciton, confined in a^M quantum disk, are calculated as a function of an external magnetic field. The confinement potential is a hard wall of finite height. The diamagnetic shift is investigated for magnetic fields up to 40$T$. Our results are applied to $In_{y}Al_{1-y}As/Al_{x}Ga_{1-x}As$ self-assembled quantum dots and very good agreement with experiments is obtained. Furthermore, we investigated the influence of the dot size on the diamagnetic shift by changing the disk radius. The exciton excited states are found as a function of the magnetic field. The relative angular momentum is not a quantum number and changes with the magnetic field strength.Comment: 10 pages, 17 figure

Tunable photon statistics exploiting the Fano effect in a waveguide

A strong optical nonlinearity arises when coherent light is scattered by a semiconductor quantum dot (QD) coupled to a nano-photonic waveguide. We exploit the Fano effect in such a waveguide to control the phase of the quantum interference underpinning the nonlinearity, demonstrating a tunable quantum optical filter which converts a coherent input state into either a bunched, or antibunched non-classical output state. We show theoretically that the generation of non-classical light is predicated on the formation of a two-photon bound state due to the interaction of the input coherent state with the QD. Our model demonstrates that the tunable photon statistics arise from the dependence of the sign of two-photon interference (either constructive or destructive) on the detuning of the input relative to the Fano resonance

High Purcell factor generation of coherent on-chip single photons

On-chip single-photon sources are key components for integrated photonic quantum technologies. Semiconductor quantum dots can exhibit near-ideal single photon emission but suffer from significant dephasing in on-chip geometries owing to nearby etched surfaces. A long-proposed solution is to use the Purcell effect of an optical nanocavity to reduce the radiative lifetime to much less than dephasing timescales. However, until now only modest Purcell enhancements have been observed. Here we use resonant excitation to eliminate slow relaxation paths, revealing a highly Purcell-enhanced radiative lifetime of only 22.7 ps. This is measured by applying a novel high-time-resolution double $\pi$-pulse resonance fluorescence technique to a quantum dot in a waveguide-coupled photonic crystal cavity. Coherent scattering measurements confirm the short lifetime and show that the quantum dot exhibits near-radiatively-limited coherence. Under $\pi$-pulse excitation, the waveguide coupling enables demonstration of an on-chip, on-demand single-photon source exhibiting high purity and indistinguishability without spectral filtering

Theory of Nonlinear Transport for Ensembles of Quantum Dots

This article reviews our work on the description of electronic transport through self-assembled quantum dots. Our main interest is in the effect of Coulomb interaction on quantum dot charging (capacitance-voltage characteristics), on the average current (current-voltage characteristics), and on current fluctuations (quantum shot noise) in quantum dot layers embedded in pn- or resonant tunneling devices. Our studies show the particular importance of understanding those interaction mechanisms for future device applications