arXiv subjects

A. P. Foster

Publications and source records attributed to A. P. Foster.

7 recordsLinked to original sources

arXiv2022

Engineering strong chiral light-matter interactions in a waveguide-coupled nanocavity

Spin-dependent, directional light-matter interactions form the basis of chiral quantum networks. In the solid state, quantum emitters commonly possess circularly polarised optical transitions with spin-dependent handedness. We demonstrate numerically that spin-dependent chiral coupling can be realised by embedding such an emitter in a waveguide-coupled nanocavity, which supports two near-degenerate, orthogonally-polarised cavity modes. The chiral behaviour arises due to direction-dependent interference between the cavity modes upon coupling to two single-mode output waveguides. Notably, an experimentally realistic cavity design simultaneously supports near-unity chiral contrast, efficient ($β> 0.95$) waveguide coupling and enhanced light-matter interaction strength (Purcell factor $F_P > 70$). In combination, these parameters could enable the development of highly coherent spin-photon interfaces, ready for integration into nanophotonic circuits.

physics.optics↗

arXiv2021

A chiral topological add-drop filter for integrated quantum photonic circuits

The integration of quantum emitters within topological nano-photonic devices opens up new avenues for the control of light-matter interactions at the single photon level. Here, we realise a spin-dependent, chiral light-matter interface using individual semiconductor quantum dots embedded in a topological add-drop filter. The filter is imprinted within a valley-Hall photonic crystal (PhC) membrane and comprises a resonator evanescently coupled to a pair of access waveguides. We show that the longitudinal modes of the resonator enable the filter to perform wavelength-selective routing of light, protected by the underlying topology. Furthermore, we demonstrate that for a quantum dot located at a chiral point in the resonator, selective coupling occurs between well-defined spin states and specific output ports of the topological device. This behaviour is fundamental to the operation of chiral devices such as a quantum optical circulator. Our device therefore represents a topologically-protected building block with potential to play an enabling role in the development of chiral integrated quantum photonic circuits.

physics.optics↗

arXiv2020

A Semiconductor Topological Photonic Ring Resonator

Unidirectional photonic edge states arise at the interface between two topologically-distinct photonic crystals. Here, we demonstrate a micron-scale GaAs photonic ring resonator, created using a spin Hall-type topological photonic crystal waveguide. Embedded InGaAs quantum dots are used to probe the mode structure of the device. We map the spatial profile of the resonator modes, and demonstrate control of the mode confinement through tuning of the photonic crystal lattice parameters. The intrinsic chirality of the edge states makes them of interest for applications in integrated quantum photonics, and the resonator represents an important building block towards the development of such devices with embedded quantum emitters.

physics.optics↗

arXiv2019

Tunable photon statistics exploiting the Fano effect in a waveguide

A strong optical nonlinearity arises when coherent light is scattered by a semiconductor quantumdot (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, experimentally 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.

quant-ph↗

arXiv2018

Electro-mechanical control of an on-chip optical beam splitter containing an embedded quantum emitter

We demonstrate electro-mechanical control of an on-chip GaAs optical beam splitter containing a quantum dot single-photon source. The beam splitter consists of two nanobeam waveguides, which form a directional coupler (DC). The splitting ratio of the DC is controlled by varying the out-of-plane separation of the two waveguides using electro-mechanical actuation. We reversibly tune the beam splitter between an initial state, with emission into both output arms, and a final state with photons emitted into a single output arm. The device represents a compact and scalable tuning approach for use in III-V semiconductor integrated quantum optical circuits.

physics.app-ph↗

arXiv2017

Electrical control of nonlinear quantum optics in a nano-photonic waveguide

Local control of the generation and interaction of indistinguishable single photons is a key requirement for photonic quantum networks. Waveguide-based architectures, in which embedded quantum emitters act as both highly coherent single photon sources and as nonlinear elements to mediate photon-photon interactions, offer a scalable route to such networks. However, local electrical control of a quantum optical nonlinearity has yet to be demonstrated in a waveguide geometry. Here, we demonstrate local electrical tuning and switching of single photon generation and nonlinear interaction by embedding a quantum dot in a nano-photonic waveguide with enhanced light-matter interaction. A power-dependent transmission extinction as large as 40$\pm$2% and clear, voltage-controlled bunching in the photon statistics of the transmitted light demonstrate the single photon character of the nonlinearity. The deterministic nature of the nonlinearity is particularly attractive for the future realization of photonic gates for scalable nano-photonic waveguide-based quantum information processing.

quant-ph↗

arXiv2016

Electrically pumped single-defect light emitters in WSe$_2$

Recent developments in fabrication of van der Waals heterostructures enable new type of devices assembled by stacking atomically thin layers of two-dimensional materials. Using this approach, we fabricate light-emitting devices based on a monolayer WSe$_2$, and also comprising boron nitride tunnelling barriers and graphene electrodes, and observe sharp luminescence spectra from individual defects in WSe$_2$ under both optical and electrical excitation. This paves the way towards the realization of electrically-pumped quantum emitters in atomically thin semiconductors. In addition we demonstrate tuning by more than 1 meV of the emission energy of the defect luminescence by applying a vertical electric field. This provides an estimate of the permanent electric dipole created by the corresponding electron-hole pair. The light-emitting devices investigated in our work can be assembled on a variety of substrates enabling a route to integration of electrically pumped single quantum emitters with existing technologies in nano-photonics and optoelectronics.

physics.optics↗