Electrically Driven Site-Controlled Single Photon Source.

Single photon sources are fundamental building blocks for quantum communication and computing technologies. In this work, we present a device geometry consisting of gold pillars embedded in a van der Waals heterostructure of graphene, hexagonal boron nitride, and tungsten diselenide. The gold pillars serve to both generate strain and inject charge carriers, allowing us to simultaneously demonstrate the positional control and electrical pumping of a single photon emitter.

Inverse Design of Whispering-Gallery Nanolasers with Tailored Beam Shape and Polarization.

Control over the shape and polarization of the beam emitted by a laser source is important in applications such as optical communications, optical manipulation and high-resolution optical imaging. In this paper, we present the inverse design of monolithic whispering-gallery nanolasers which emit along their axial direction with a tailored laser beam shape and polarization. We design and experimentally verify three types of submicron cavities, each one emitting into a different laser radiation mode: an azimuthally polarized doughnut beam, a radially polarized doughnut beam and a linearly polarized Gaussian-like beam.

Coherence protection of spin qubits in hexagonal boron nitride.

Spin defects in foils of hexagonal boron nitride are an attractive platform for magnetic field imaging, since the probe can be placed in close proximity to the target. However, as a III-V material the electron spin coherence is limited by the nuclear spin environment, with spin echo coherence times of ∽100 ns at room temperature accessible magnetic fields. We use a strong continuous microwave drive with a modulation in order to stabilize a Rabi oscillation, extending the coherence time up to ∽ 4μs, which is close to the 10 μs electron spin lifetime in our sample.

Excited State Spectroscopy of Boron Vacancy Defects in Hexagonal Boron Nitride Using Time-Resolved Optically Detected Magnetic Resonance.

We report optically detected magnetic resonance (ODMR) measurements of an ensemble of spin-1 negatively charged boron vacancies in hexagonal boron nitride. The photoluminescence decay rates are spin-dependent, with intersystem crossing rates of 1.02 ns and 2.

Stimulated Emission Depletion Spectroscopy of Color Centers in Hexagonal Boron Nitride.

We demonstrate the use of Stimulated Emission Depletion (STED) spectroscopy to map the electron-optical-phonon sideband of the ground state of the radiative transition of color centers in hexagonal boron nitride emitting at 2.0-2.2 eV, with in-plane linear polarization.

Single vs double anti-crossing in the strong coupling between surface plasmons and molecular excitons.

Strong coupling between surface plasmons and molecular excitons may lead to the formation of new hybrid states-polaritons-that are part light and part matter in character. A key signature of this strong coupling is an anti-crossing of the exciton and surface plasmon modes on a dispersion diagram. In a recent report on strong coupling between the plasmon modes of a small silver nano-rod and a molecular dye, it was shown that when the oscillator strength of the exciton is large enough, an additional anti-crossing feature may arise in the spectral region where the real part of the permittivity of the excitonic material is zero.

Optical Gating of Photoluminescence from Color Centers in Hexagonal Boron Nitride.

We report on multicolor excitation experiments with color centers in hexagonal boron nitride at cryogenic temperatures. We demonstrate controllable optical switching between bright and dark states of color centers emitting around 2 eV. Resonant, or quasi-resonant, excitation of photoluminescence also pumps the color center, via a two-photon process, into a dark state, where it becomes trapped.

Gate tunable graphene-integrated metasurface modulator for mid-infrared beam steering.

The ability to integrate graphene into metasurface devices has attracted enormous interest as a means of achieving dynamic electrical control of their electromagnetic response. In this manuscript, we experimentally demonstrate a graphene-integrated metasurface modulator that establishes the potential to actively control the amplitude and phase of mid-infrared light with high modulation depth and speed, in good agreement with simulation results. Our simulations also show it is possible to construct a reconfigurable surface with tunable phase profile by incorporating graphene-integrated metasurface modulators with specific geometric parameters.

Metamaterial-enhanced infrared attenuated total reflection spectroscopy.

The use of Fourier transform infrared spectroscopy with attenuated total reflection (FTIR-ATR) allows solid or liquid samples to be characterised directly without specific sample preparation. In such a system, the evanescent waves generated through total internal reflection within a crystal interact with the sample under test. In this work we explore the use of a mid-infrared metasurface to enhance the interaction between molecular vibrations and the evanescent waves.

Highly tunable hybrid metamaterials employing split-ring resonators strongly coupled to graphene surface plasmons.

Metamaterials and plasmonics are powerful tools for unconventional manipulation and harnessing of light. Metamaterials can be engineered to possess intriguing properties lacking in natural materials, such as negative refractive index. Plasmonics offers capabilities of confining light in subwavelength dimensions and enhancing light-matter interactions.

Waveguide coupled resonance fluorescence from on-chip quantum emitter.

Resonantly driven quantum emitters offer a very promising route to obtain highly coherent sources of single photons required for applications in quantum information processing (QIP). Realizing this for on-chip scalable devices would be important for scientific advances and practical applications in the field of integrated quantum optics. Here we report on-chip quantum dot (QD) resonance fluorescence (RF) efficiently coupled into a single-mode waveguide, a key component of a photonic integrated circuit, with a negligible resonant laser background and show that the QD coherence is enhanced by more than a factor of 4 compared to off-resonant excitation.

Waveguide-coupled photonic crystal cavity for quantum dot spin readout.

We present a waveguide-coupled photonic crystal H1 cavity structure in which the orthogonal dipole modes couple to spatially separated photonic crystal waveguides. Coupling of each cavity mode to its respective waveguide with equal efficiency is achieved by adjusting the position and orientation of the waveguides. The behavior of the optimized device is experimentally verified for where the cavity mode splitting is larger and smaller than the cavity mode linewidth.

III-V quantum light source and cavity-QED on silicon.

Non-classical light sources offer a myriad of possibilities in both fundamental science and commercial applications. Single photons are the most robust carriers of quantum information and can be exploited for linear optics quantum information processing. Scale-up requires miniaturisation of the waveguide circuit and multiple single photon sources.

Interfacing spins in an InGaAs quantum dot to a semiconductor waveguide circuit using emitted photons.

An in-plane spin-photon interface is essential for the integration of quantum dot spins with optical circuits. The optical dipole of a quantum dot lies in the plane and the spin is optically accessed via circularly polarized selection rules. Hence, a single waveguide, which can transport only one in-plane linear polarization component, cannot communicate the spin state between two points on a chip.

Effect of a GaAsP shell on the optical properties of self-catalyzed GaAs nanowires grown on silicon.

We realize the growth of self-catalyzed core-shell GaAs/GaAsP nanowires (NWs) on Si substrates using molecular-beam epitaxy. Transmission electron microscopy of single GaAs/GaAsP NWs demonstrates their high crystal quality and shows domination of the GaAs zinc-blende phase. Using continuous-wave and time-resolved photoluminescence (PL), we make a detailed comparison with uncapped GaAs NWs to emphasize the effect of the GaAsP capping in suppressing the nonradiative surface states.

Coherent optical control of the spin of a single hole in an InAs/GaAs quantum dot.

We demonstrate coherent optical control of a single hole spin confined to an InAs/GaAs quantum dot. A superposition of hole-spin states is created by fast (10-100 ps) dissociation of a spin-polarized electron-hole pair. Full control of the hole spin is achieved by combining coherent rotations about two axes: Larmor precession of the hole spin about an external Voigt geometry magnetic field, and rotation about the optical axis due to the geometric phase shift induced by a picosecond laser pulse resonant with the hole-trion transition.

Electrical properties of individual CoPt/Pt multilayer nanowires characterized by in situ SEM nanomanipulators.

Here we report for the first time accurate and comprehensive measurements of electrical properties of individual CoPt/Pt multilayer nanowires both with periodic and non-periodic layer structures. A remarkably high failure current density of 1.69 × 10(12) A m(-2) for the periodic MNW and a similar 1.

A p-type-doped quantum dot superluminescent LED with broadband and flat-topped emission spectra obtained by post-growth intermixing under a GaAs proximity cap.

Broadband superluminescent light emitting diodes are realized by a post-growth annealing process, on modulation p-doped multiple InAs/InGaAs/GaAs quantum dot layer structures, under a GaAs proximity cap. The device exhibits a large and flat emission with spectral width up to 132 nm at 2 mW. This is mainly attributed to the reduction of the energy separation between the ground state and the excited state, in addition to the optical quality of the intermixed modulation p-doped quantum dot materials being comparable to that of the as-grown sample.