Optically addressable spins in materials are important platforms for quantum technologies, such as repeaters and sensors. Identification of such systems in two-dimensional (2d) layered materials offers advantages over their bulk counterparts, as their reduced dimensionality enables more feasible on-chip integration into devices. Here, we report room-temperature optically detected magnetic resonance (ODMR) from previously identified carbon-related single defects in 2d hexagonal boron nitride (hBN). We show that single-defect ODMR contrast is up to 100x stronger than that of ensembles and displays a magnetic-field dependence with both positive or negative sign per defect. Further, the ODMR lineshape comprises a doublet resonance, indicating a S=1 state with low but finite zero-field splitting. Our results offer a promising route towards realising a room-temperature spin-photon quantum interface in hexagonal boron nitride.

This Conference Presentation, “Nonlinear plasmonics in atomically-thin materials”, was recorded at SPIE Photonics West 2022 held in San Francisco, California, United States.

Nonlinear optical processes resulting from light-matter interaction are essential for control of light by light in photonic technologies. Here, based on first-principles calculations, we investigate the linear and nonlinear optical response of monolayer hBN in the mid-infrared polaritonic region following time-domain and perturbative schemes, from which we conclude an extraordinarily large nonlinear response, which can be modulated by lateral electrical gating and presents an opportunity to achieve quantum blockade at the level of a few quanta. Our study reveals a range of potential applications that include harmonic generation, optical modulation, and quantum information in the mid-infrared range.

We present here experimental investigations of 2D material integrated with large area laterally confined heterostructure photonic crystal (PC) cavities. Both exfoliated and CVD synthesized WS2 materials have been investigated. Room temperature lasing was achieved for both material systems, with narrow spectral linewidth and highly directional emission. Multi-wavelength lasing was achieved through high yield transfer printing of large area CVD WS2 material onto photonic crystal cavity arrays. The scaling challenges of gain and laser cavities will also be discussed with the ultimate goal of attojoule lasers.

Here, we demonstrate a 2D p–n van der Waals heterojunction photodetector constructed by vertically stacking p-type and n-type few-layer indium selenide (InSe) 2D flakes. This heterojunction charge-separation-based photodetector shows a three-fold enhancement in responsivity at near-infrared spectral region (980 nm) as compared to a photoconductor detector based on p- or n-only doped regions, respectively. We show, that this junction device exhibits self-powered photodetection operation and hence enables few pA-low dark currents, which is about 3-4 orders of magnitude more efficient than state-of-the-art foundry-based devices. Such capability opens doors for small signal-to-noise environments and low photon-count detectability without having to rely on external gain. We further demonstrate millisecond response rates in this sensitive zero-bias voltage regime.

Here we present our latest PIC-integrated TMD-based slot-enhanced photodetector. The metallic slot enhances the light-matter-interaction and hence absorption into the semiconductor TMD layer. Unlike Graphene detectors, this device based on a 1+eV wide Eg detector (MoTe2) shows a low dark-current Of 100’s pA (i.e. 3 orders of magnitude lower than graphene). Utilizing the plasmonic slot allows to harness scaling effects known from FETs, and reduce carrier transit times. Thus, we demonstrate 10GHz roll-offs despite a rather low mobility. We further show that the short-channel allows for near-ballistic transport, and more importantly high gain-bandwidth-products (GPB), which scales with the source-drain distance squared. The combination of a TMD semiconductor with a slot for short transit times, enables we new class of efficient yet compact PIC-integrated detectors offering high GBP.

Monolayer transition-metal dichalcogenides (TMDs) are the first truly two-dimensional (2D) semiconductor, providing an excellent platform to investigate light−matter interaction in the 2D limit. The inherently strong excitonic response in monolayer TMDs can be further enhanced by exploiting the temporal confinement of light in nanophotonic structures. Here, we demonstrate a 2D exciton−polariton system by strongly coupling atomically thin tungsten diselenide (WSe2) monolayer to a silicon nitride (SiN) metasurface. Via energy-momentum spectroscopy of the WSe2-metasurface system, we observed the characteristic anticrossing of the polariton dispersion both in the reflection and photoluminescence spectrum. A Rabi splitting of 18 meV was observed which matched well with our numerical simulation.

Polaritons in 2D materials are fundamentally interesting for different technological applications, but their coupling to light is generally weak due to their momentum mismatch. In this work, we remarkably show that a small scatterer placed at a suitable distance from a given surface can couple light completely into the surface modes supported by the surface, under illumination by a modulated field. We present rigorous closed-form prescriptions for the modulation of the incident light beam which maximizes this coupling, depending on the characteristics of the scatterer and surface, and use the derived expressions to provide a rigorous theoretical analysis of the extremal light coupling to plasmons in different 2D materials (namely thin metals and graphene). We corroborate the analytical results by performing fully-numerical simulations using realistic setups, which exhibit a very strong enhancement of the absorption into surface plasmons under the prescribed optimal conditions.

Due graphene’s robustness as an element in a variety of optoelectronic and photonic platforms, the material can be coupled to other resonant structures to realize functionality beyond that predicted by its constituent optical properties alone. Here we demonstrate a tunable graphene metasurface that exhibits near-unity absorptance over a narrowband range of wavelengths. We hybridize a guided mode resonance of a silicon photonic crystal with the localized surface plasmon of a graphene ribbon to produce a critically coupled system. We investigate various geometric configurations to realize a diversity of Fano lineshapes and incorporate coupled mode theory to quantitatively describe our results.

The scalable and patterned growth of two-dimensional (2D) quantum materials is essential for wafer-scale device integration in order to transition their exciting properties and performance from lab to fab. However, the current gas-phase synthesis methods are incompatible with conventional patterning technologies (e.g., lithography) or require extensive top-down processing steps (e.g., etching) to create the desired device structures on the substrates. In this talk, I will describe some of the laser-based approaches we are undertaking to control the synthesis and integration of various 2D materials. I will particularly highlight our recently developed condensed phase growth approach compatible with direct laser writing as well as the conventional lithography and device integration technologies.

Recent progress in the fabrication of metallic thin films allows for a precise control of the surface crystallographic orientation and thickness, turning them to be a great appeal in plasmonic devices. Considering such a crystalline quality and going towards smaller optical designs; surface, nonlocal, and quantum finite-size effects play a major role in metallic thin films when interacting with light. Here we explore various strategies to seek for the linear and nonlinear optical response manifested in a variety of scenarios and configurations which are based on precise quantum-mechanical formalisms that describe the dynamics of electrons in such films, e.g. EELS, Feibelman d-parameters, periodic- and finite-systems, etc. We believe that our results can inspire future devices based on crystalline metal films as well as motivate further numerical implementation strategies.