Microcavity exciton-polaritons are bosonic quasiparticles that result from the hybridization of excitons and modes of a confined electromagnetic field in a regime known as strong light-matter coupling. Having a low effective mass, polaritons can undergo condensation, the macroscopic occupation of the lowest energy and momentum state. Two-dimensional (2D) perovskites are promising candidates for polariton condensation due to their high exciton binding energies, low non-radiative recombination rates and strong oscillator strengths. However, despite their optimal optoelectronic properties, there are no reports of room temperature polariton condensation in 2D perovskites and only one unreproduced report at low temperature. In this study, we systematically examine the interplay between the emission from the exciton reservoir and the population of the lower polariton. We gain insights on how the spectral features of the emission of 2D perovskites affect polariton relaxation and onto one of the mechanisms making polariton condensation challenging in 2D perovskites.
The emergence of van der Waals (vdW) magnets with strongly coupled electronic and spin degrees of freedom offers an intriguing platform to study light-matter interaction in low-dimensional magnets. Specifically, magnetic materials that host excitons in the visible frequencies with strong correlation to underlying magnetic order are very attractive in this context. I will present our recent work on realizing exciton-polaritons (strongly coupled light-matter states) in such magnetic systems and the prospects of controlling the magneto-optical response with light [1, 2]. I will conclude with a discussion on realizing active nanophotonic devices using vdW magnets.
[1] “Observation of spin-correlated exciton-polaritons in a van der Waals magnet, F. Dirnberger, et al. Nature Nanotechnology 17, 1060 (2022)
[2] “Cavity-controlled magneto-optical properties of a strongly coupled van der Waals magnet,” F. Dirnberger et al. arXiv:2301.07593 (2023)
Strong light-matter coupling enabled polariton states were extensively exploited for enhanced optical nonlinearities, development of low threshold lasers and quantum simulators. Here, we will report our recent work on demonstration of novel topological polaritonic phases by leveraging the strong coupling between the photonic topological boundary states and two different material degrees of freedom in 2D Van der Waals materials; first transverse optical phonons in a hexagonal boron nitride (hBN) thin film and second excitons in 2D WSe2 monolayer. Our results will demonstrate emergence of topological boundary states of phonon-polariton and exciton-polariton character, and their resilient unidirectional propagation around sharp corner with avoided backscattering.
Strong light-matter interaction results in the formation of polaritons, quasiparticles that take on the properties of both light and material excitations. In this talk we will discuss our recent work on coupling of magnetically correlated excitons in van der Waals magnets with cavity photons. The prospects for modifying magneto-optical response and realizing opto-magnetic devices based on these magneto-polaritons will also be discussed.
Here we directly emulate a two-dimensional Dirac equation with a position-dependent mass term in a photonic crystal and present a new type of photonic resonators with light confinement originating in relativistic Dirac physics. Some of the modes of such resonators represent eigenmodes of a supersymmetric Hamiltonian. To test our concept, we designed, fabricated, and studied a resonator operating in the mid-IR region. Direct imaging of the structure in both real and Fourier spaces confirmed existence of the modes. The demonstrated approach offers a new route for designing photonic devices and probing supersymmetric quantum physics by using a classical photonic platform.
We report novel topological polaritonic states of half-light and half-phonon character in a topological mid-infrared metasurface integrating hexagonal boron nitride (hBN). A custom-built Fourier-space imaging microscope was used to investigate a three-dimensional band diagram of the photonic topological phonon-polaritonic states in our system for the first time. Our Fourier- and real-space imaging experimental findings, supported by theoretical models, demonstrate that topological properties of photonic modes are transcribed to the in-plane lattice vibrations (phonons) supported by hBN. As a result, the observed topological phonon-polaritons exhibit unidirectional propagation with the helical nature of vibrations and the resilience of the modes to sharp bends.
The WS2 monolayer encapsulated in two thin hBN layers was pumped at room temperature by a circularly polarized laser in order to excite one of the valleys (K or K’ valley). The refractivity spectra measured using both left- and right- CP probe with low intensity, revealed the nonreciprocal response at exciton resonance wavelength. Based on this effect, we propose a novel design of an isolator containing SiN ring resonator integrating an asymmetrically places WS2 monolayer. By applying the coupled mode theory and parameter extracted from the experiment, the isolation of the device was estimated to be ~20dB.
The concept of modifying molecular dynamics in strongly coupled exciton-polariton systems is an emerging topic in photonics. However, there is no consensus on the types of molecular systems whose dynamics can be modified using strong coupling. These open questions stem from persistent uncertainties concerning the lifetime and conversion dynamics of exciton-polaritons and localized excited states as well as the proper way to measure such interactions in the time-domain. Here, we provide a framework for measuring dynamical interactions between exciton-polaritons and a diverse manifold of singlet, triplet, and multiexciton states, using a model molecular spin conversion (singlet fission) system that is strongly coupled to an optical microcavity. In addition to the usual population dynamics, transient optical measurements on microcavities are sensitive to transient modifications of the exciton-polariton transition energies, exciton-photon coupling conditions, and thermal excitations of the cavity mirrors.
Single photon sources (quantum emitters) are a key building block for emerging quantum technologies. Especially attractive for quantum photonic circuitry is the prospect of integrating such sources with conventional photonic structures such as resonators and waveguides. In this talk, we will first present our work on realizing single photon emitters (SPEs) in hexagonal boron nitride (hBN), a van der Waals material, via strain engineering. Following this we will discuss the coupling of such SPEs to silicon nitride microdisk resonators and to plasmonic surface lattice resonances. Prospects of realizing electrically driven SPEs using few layer hBN placed in van der Waals heterostructures will also be discussed.
Two-dimensional van der Waals (vdW) materials have emerged as a very attractive class of optoelectronic material due to their extraordinarily strong interaction with light. In this talk we will present our recent work on strong light-matter coupling and control of the excitons in 2D transition metal dichalcogenides. Specifically, we will discuss nonlinear optical response of the strongly coupled states, control of chiral light-matter interaction in these materials using metamaterials, and the use of strain and artifical gauge fields to control transport and valley properties of the excitons.
In this talk we will discuss our recent work on electrical and optical control of strongly-coupled exciton-polaritons in two-dimensional Van der Waals materials. The possibility to optically address the valley degree of freedom of polariton states via optical excitation will be discussed [1]. Following this we will discuss the modulation of coupling strength between excitons and photons in a microcavity via electric field [2]. The possibility to enhance the nonlinear optical response of the polariton states by exploiting the higher order Rydberg states will also be presented. Finally, we will discuss the realization of room temperature quantum emitter array using strain engineered hexagonal boron nitride and coupling them to high quality factor resonators [3].
[1] Optical control of room temperature valley polaritons, Z. Sun, et al., Nature Photonics 11, 491 (2017).
[2] Control of strong light-matter interaction in monolayer WS2 through electric field gating, B. Chakraborty et al., Nano. Lett. (2018) DOI: 10.1021/acs.nanolett.8b02932
[3] Near-deterministic activation of room temperature quantum emitters in hexagonal boron nitride, N. Proscia et al. Optica (In Press) [ArXiv: 1712.01352 ]
In this talk we will discuss our recent work on strong light-matter coupling of excitons in two-dimensional Van der Waals materials [1, 2]. Formation of microcavity exciton-polaritons at room temperature in these materials and their valley polarization properties will be discussed. Prospects for electrical control and the nonlinear optical properties of the polariton states will also be addressed. Finally, we will also discuss the formation of room-temperature quantum emitters via strain engineering in these materials.
[1] Strong light-matter coupling in two-dimensional atomic crystals, X. Liu, et al., Nature Photonics 9, 30 (2015)
[2] Optical control of room temperature valley polaritons, Z. Sun, et al., Nature Photonics 11, 491 (2017).
Photonic crystals and metamaterials have emerged as the most widely used artificial media for controlling light-matter interaction in solid state systems. The former relies on Bragg scattering from wavelength sized periodic modulation in the dielectric environment while the latter has sub-wavelength sized sub-structures that are designed to give an effective medium response. Here we report a new class of artificial photonic media: “photonics hypercrystals” for control of light matter interaction. Hypercrystals are distinct from photonic crystals, as both material scales involved - the hypercrystal period and the unit cells of its material components - are sub-wavelength. And they are also not metamaterials, as their electromagnetic response is qualitatively different from the expected averaged behavior. This fundamental difference results in a number of nontrivial electromagnetic properties of the hypercrystals, that can be observed in experiment and even lead to practical devices - from broadband enhancement of spontaneous emission and light out-coupling which has never to date been demonstrated simultaneously in either metamaterials or photonic crystals, to Dirac physics and singularities in sub-wavelength sized lattice. Specifically, we demonstrate enhanced spontaneous emission rate (x20) and light out-coupling (x100) from a two-dimensional metal-dielectric hypercrystal embedded with quantum dots. Such designer photonic media with complete control over the optical properties provide a new platform for broadband control of light-matter interaction.
In this talk we will discuss our recent work on the formation of organic-inorganic hybrid excitons in microcavities as well as the nonlinear optical response of hybrid excitonic systems. Using thin film 3,4,7,8-napthalenetetracarboxylic dianhydride (NTCDA) and ZnO nanocrystals/nanowires we demonstrate enhanced Rabi splitting of hybrid polaritons and improved third order nonlinear optical response. In the former case, the hybrid materials are embedded in an optical microcavity.
Transition metal dichalcogenides (TMDs) have emerged as an attractive class of two-dimensional (2D) semiconductors that show unprecedented strength in its interaction with light. Here we will discuss our recent work on embedding such a 2D TMD layer of molybdenum disulphide in a dielectric microcavity showing the forming of strongly coupled half-light half-matter quasiparticles called microcavity polaritons. Realizing strong coupling at room temperature in a disorder free landscape such as 2D materials offers a practical and attractive route to realizing devices such as switches and logic gates that exploit the benefits of the half-light half-matter composition of the polaritons.
Hyperbolic metamaterials (HMMs) have become one of the most attractive classes of metamaterials due to their wide array of applications in combination with ease of realization. Here we will discuss our recent work on “active hyperbolic metamaterials” where demonstrate enhanced light emission and extraction from metamaterials embedded with quantum dots. We will also discuss our recent efforts on realizing tunable HMMs as well as sub-wavelength cavities.
Results are presented here towards robust room-temperature SPSs based on fluorescence in nanocrystals: colloidal
quantum dots, color-center diamonds and doped with trivalent rare-earth ions (TR3+). We used cholesteric chiral
photonic bandgap and Bragg-reflector microcavities for single emitter fluorescence enhancement. We also developed
plasmonic bowtie nanoantennas and 2D-Si-photonic bandgap microcavities. The paper also provides short outlines of
other technologies for room-temperature single-photon sources.
Integrated photonic devices were realized using colloidal quantum dot composites such as flexible microcavity laser, microdisk emitters and integrated active-passive waveguides. The microcavity laser structure was realized using spin coating and consisted of an all-polymer distributed Bragg reflector with a poly-vinyl carbazole cavity layer embedded with InGaP/ZnS colloidal quantum dots. These microcavities can be peeled off the substrate yielding a flexible structure that can conform to any shape and whose emission spectra can be mechanically tuned. Planar photonic devices consisting of vertically coupled microring resonators, microdisk emitters, active-passive integrated waveguide structures and coupled active microdisk resonators were realized using soft lithography, photo-lithography, and electron beam lithography, respectively. The gain medium in all these devices was a composite consisting of quantum dots embedded in SU8 matrix. Finally, the effect of the host matrix on the optical properties of the quantum dots using results of steady-state and time-resolved luminescence measurements was determined. In addition to their specific functionalities, these novel device demonstrations and their development present a low-cost alternative to the traditional photonic device fabrication techniques.
We discuss our work on light emitters and photonic circuits realized using colloidal quantum dot composites.
Specifically we will report our recent work on flexible microcavity laser, microdisk emitters and integrated active -
passive waveguides. The entire microcavity laser structure was realized using spin coating and consisted of an all-polymer
distributed Bragg reflector with a poly-vinyl carbazole cavity layer embedded with InGaP/ZnS colloidal
quantum dots. These microcavities can be peeled off the substrate yielding a flexible structure that can conform to any
shape and whose emission spectra can be mechanically tuned. The microdisk emitters and the integrated waveguide
structures were realized using soft lithography and photo-lithography, respectively and were fabricated using a
composite consisting of quantum dots embedded in SU8 matrix. Finally, we will discuss the effect of the host matrix on
the optical properties of the quantum dots using results of steady-state and time-resolved luminescence measurements. In
addition to their specific functionalities, these novel device demonstrations and their development present a low cost
alternative to the traditional photonic device fabrication techniques.
We propose to develop a submillimeter quantum cascade laser in the GaAs/AlGaAs material system. This device relies on intersubband transitions in GaAs quantum wells of the device for lasing. Preliminary calculations show that there is sufficient gain to produce lasing in the wavelength range 80 to 125 micrometer. The active region of the laser structure consists of coupled quantum wells which can be grown by molecular beam epitaxy (MBE). The model uses a 30 nm-wide active quantum well which contains two levels separated by 14.8 meV which corresponds to a wavelength of 83.5 micrometer at a bias of 8850 V/cm with 12.2 nm and 29.8 nm wide quantum well energy filters inserted on either side of the active well. The energy filters are designed to allow only electrons with the energy of the upper state to be injected into the active well and only electrons with the energy of the lower state to be extracted from the active well. The proposed device uses a 10-period injector/active well/collector structure. The collector/injector is a superlattice region, which acts as a reservoir for the electrons. The gain of this system has been calculated to be approximately 2500 cm-1. Threshold current density has been calculated to be about 622 A/cm2 at 77 K.
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