arXiv subjects

Luke R. Wilson

Publications and source records attributed to Luke R. Wilson.

8 recordsLinked to original sources

arXiv2026

Near-Field Characterisation of Guided Modes in WS2 Nanobeams and Quasi-Bulk Crystals

The exceptionally high in-plane refractive index, low sub-bandgap absorption, and strong optical anisotropy of WS2 make it a promising material platform for next-generation integrated circuits for nanophotonics. Its layered van der Waals structure further enables heterogeneous integration with silicon photonics and emerging two-dimensional optoelectronic materials. However, despite increasing interest in the waveguiding properties of WS2, experimental studies of wavelength-dependent modal confinement and attenuation remain limited. Additionally, though the extinction coefficient of WS2 is expected to be near-negligible beneath the bandgap, reported values span orders of magnitude, leading to large uncertainty in predicted modal decay lengths and wafer-scale integration feasibility. To resolve these ambiguities we perform hyperspectral cavity-enhanced imaging, determining high-resolution upper and lower bounds on the extinction coefficient of WS2 within the visible-NIR edge. We further employ scattering-type scanning near-field optical microscopy (s-SNOM) to probe TE0, TM0, and higher-order modes in both quasi-bulk and nanobeam WS2 waveguides across the 800-1400 nm spectral range, enabling identification of mode-specific trends in wavevector dispersion and loss. This work simultaneously assesses s-SNOM as a probe of waveguide performance, and we find that while absolute loss values depend on measurement geometry, s-SNOM reliably captures relative modal trends and provides upper bounds on propagation loss, supporting its use as a diagnostic tool for anisotropic waveguides. We further identify significant artefacts in nanobeam measurements arising from transverse interference and spatial sampling effects when the structure size approaches the excitation wavelength, which can shift extracted effective indices by up to 0.25.

physics.optics↗

arXiv2026

Observation of Electrically Tunable Chirality Inversion in a Slow-Light Waveguide

We identify chiral inversion points in slow-light, glide-plane-symmetric, photonic-crystal waveguides, defined as fixed locations where the local optical chirality changes sign over a narrow wavelength range. We experimentally access this behaviour using a waveguide-embedded InAs/InGaAs quantum dot. The slow-light spectral region is determined from time-integrated and time-resolved photoluminescence, and the dot exciton is electrically tuned across the slow-light bandwidth via the quantum-confined Stark effect. As the emission wavelength is swept through the slow-light region, the directional emission contrast shows a strong wavelength dependence and a sign reversal, consistent with the identified chiral inversion point. Numerical simulations attribute the switching primarily to the pronounced spectral variation of the local optical chirality for emitters displaced from the waveguide center. These results demonstrate on-demand electrical switching of chiral light-matter coupling in nanophotonic waveguides and enable tunable chiral interfaces for integrated quantum photonic devices.

physics.optics↗

arXiv2025

Routing single photons with quantum emitters coupled to nanostructures

Quantum emitters coupled to nanophotonic structures are an excellent platform for controllable single-photon scattering. The tunable light-matter interaction enables the construction of a single-photon switch -- a device that can route a single photon from an input port to a selected output port. Such single-photon switching devices can be integrated into reconfigurable photonic circuits to actively control the photon propagation direction in a quantum network. Ideally, a single-photon switch should operate with high speed, efficiency, and fidelity, preserving the state of the input photon in the routing process. This review brings together key input-output methods from quantum optics, theoretical proposals of emitter-based single-photon routing mechanisms, and experimental demonstrations of single-photon switching devices across different physical platforms, including semiconductor quantum dots, neutral atoms, superconducting qubits, and color centers. We highlight the need for reporting the key figures of merit (speed/efficiency/fidelity) in future single-photon switch demonstrations to support further developments in the field.

quant-ph↗

arXiv2025

Electro-mechanically tunable, waveguide-coupled photonic-crystal cavities with embedded quantum dots

On-chip micro-cavities with embedded quantum emitters provide an excellent platform for high-performance quantum technologies. A major difficulty for such devices is overcoming the detrimental effects of fluctuations in the device dimensions caused by the limitations of the fabrication processes. We present a fully tunable system based on a 1D photonic-crystal cavity with an embedded quantum dot, which enables tuning of both the quantum dot emission energy and the cavity mode wavelength. A micro-electromechanical cantilever is used to tune the cavity mode wavelength via index modulation and the quantum-confined Stark effect is used to tune the quantum dot emission energy, mitigating the effect of fabrication imperfections. To demonstrate the operation of the device, a maximum, voltage-controllable cavity tuning range of $\Delta \lambda = 1.8$ nm is observed. This signal is measured at the end of a bus waveguide which side-couples to the cavity, enabling the coupling of multiple cavities to a common waveguide, a key requirement for scale-up in these systems. Additionally, a quantum dot is tuned into resonance with the cavity mode, exhibiting an enhanced emission rate with a resolution limited Purcell factor of $F_P = 3.5$.

physics.optics↗

arXiv2025

Waveguide Excitation and Spin Pumping of Chirally Coupled Quantum Dots

We report on an integrated semiconductor chip where a single quantum dot (QD) is excited in-plane via a photonic-crystal waveguide through its nearest p-shell optical transition. The chirality of the waveguide mode is exploited to achieve both directional absorption and directional emission, resulting in a substantial enhancement in directional contrast, as measured for the Zeeman components of the waveguide-coupled QD. This remote excitation scheme enables high directionality (greater than or equal to 0.95) across approximately 56% of the waveguide area, with significant overlap with the Purcell-enhanced region, where the electric field intensity profile is near its peak. In contrast, local excitation methods using an out-of-plane excitation beam focused directly over the area of the QD achieve only approximately 25% overlap. This enhancement increases the likelihood of locating Purcell-enhanced QDs in regions that support high directionality, enabling the experimental demonstration of a six-fold enhancement in the decay rate of a QD with greater than 90% directionality. The remote p-shell excitation protocol establishes a new benchmark for waveguide quantum optics in terms of the combination of Purcell enhancement and high directionality, thereby paving the way for on-chip excitation of spin-based solid-state quantum technologies in regimes of high beta-factor.

cond-mat.mes-hall↗

arXiv2025

Purcell-Enhanced, Directional Light-Matter Interaction in a Waveguide-Coupled Nanocavity

We demonstrate electrically tunable, spin-dependent, directional coupling of single photons by embedding quantum dots (QDs) in a waveguide-coupled nanocavity. The directional behavior arises from direction-dependent interference between two cavity modes when coupled to the device waveguides. The small mode volume cavity enables simultaneous Purcell enhancement (${10.8\pm0.7}$) and peak directional contrast (${88\pm1\%}$), exceeding current state-of-the-art waveguide-only systems. We also present a scattering matrix model for the transmission through this structure, alongside a quantum trajectory-based model for predicting the system's directionality, which we use to explain the observed asymmetry in directional contrast seen in QD devices. Furthermore, the nanocavity enables wide-range electrical tuning of the emitter's directional contrast. We present results showing precise tuning of a QD emission line from a directional contrast of ${2\%}$ to ${96\%}$. In combination, these characteristics make this cavity-waveguide approach promising for use as a building block in directional nanophotonic circuits.

physics.optics↗

arXiv2024

Efficient, High-Fidelity Single-Photon Switch Based on Waveguide-Coupled Cavities

We demonstrate theoretically that waveguide-coupled cavities with embedded two-level emitters can act as a highly efficient, high-fidelity single-photon switch. The photon switch is an optical router triggered by a classical signal -- the propagation direction of single input photons in the waveguide is controlled by changing the emitter-cavity coupling parameters in situ, for example using applied fields. The switch reflects photons in the weak emitter-cavity coupling regime and transmits photons in the strong coupling regime. By calculating transmission and reflection spectra using the input-output formalism of quantum optics and the transfer matrix approach, we obtain the fidelity and efficiency of the switch with a single-photon input in both regimes. We find that a single waveguide-coupled cavity can route input photon wave packets with near-unity efficiency and fidelity if the wave packet width is smaller than the cavity mode linewidth. We also find that using multiple waveguide-coupled cavities increases the switching bandwidth, allowing wider wave packets to be routed with high efficiency and fidelity. For example, an array of three waveguide-coupled cavities can reflect an input Gaussian wave packet with a full width at half-maximum of 1 nm (corresponding to a few-picosecond pulse) with an efficiency E_r = 96.4% and a fidelity F_r = 97.7%, or transmit the wave packet with an efficiency E_t = 99.7% and a fidelity F_t = 99.8%. Such efficient, high-fidelity single-photon routing is essential for scalable photonic quantum technologies.

quant-ph↗

arXiv2020

Chiral topological photonics with an embedded quantum emitter

Topological photonic interfaces support topologically non-trivial optical modes with helical character. When combined with an embedded quantum emitter that has a circularly polarised transition dipole moment, a chiral quantum optical interface is formed due to spin-momentum locking. Here, we experimentally realise such an interface by integrating semiconductor quantum dots into a valley-Hall topological photonic crystal waveguide. We harness the robust waveguide transport to create a ring resonator which supports helical modes. Chiral coupling of quantum dot transitions, with directional contrast as high as $75\%$, is demonstrated. The interface also supports a topologically trivial mode, comparison with which allows us to clearly demonstrate the protection afforded by topology to the non-trivial mode.

physics.optics↗