High Quality Optical Cavities Research Articles

Degeneracy and Photon Trapping in a Dissipationless Two-Mode Optomechanical Model.

In this work, we theoretically study a finite and undamped two-mode optomechanical model consisting of a high quality optical cavity containing a thin, elastic, and dielectric membrane. The main objective is to investigate the precursors of quantum phase transition in such a model by studying the behavior of some observables in the ground state. By controlling the coupling between membrane and modes, we find that the two lowest energy eigenstates become degenerate, as is indicated by the behavior of the mean value of some operators and by other quantifiers as a function of the coupling. Such degenerate states are characterized by a coherent superposition of eigenstates describing one of the two modes preferentially populated and the membrane dislocated from its equilibrium position due the radiation pressure (Schrödinger's cat states). The delocalization of the compound system photons+membrane results in an increase in fluctuations as measured by Robertson-Schrödinger uncertainty relations.

Molecular Chemistry in Cavity Strong Coupling.

The coherent exchange of energy between materials and optical fields leads to strong light-matter interactions and so-called polaritonic states with intriguing properties, halfway between light and matter. Two decades ago, research on these strong light-matter interactions, using optical cavity (vacuum) fields, remained for the most part the province of the physicist, with a focus on inorganic materials requiring cryogenic temperatures and carefully fabricated, high-quality optical cavities for their study. This review explores the history and recent acceleration of interest in the application of polaritonic states to molecular properties and processes. The enormous collective oscillator strength of dense films of organic molecules, aggregates, and materials allows cavity vacuum field strong coupling to be achieved at room temperature, even in rapidly fabricated, highly lossy metallic optical cavities. This has put polaritonic states and their associated coherent phenomena at the fingertips of laboratory chemists, materials scientists, and even biochemists as a potentially new tool to control molecular chemistry. The exciting phenomena that have emerged suggest that polaritonic states are of genuine relevance within the molecular and material energy landscape.

Squeezed light generated with hyperradiance without nonlinearity.

We propose that the squeezed light accompanied by hyperradiance is induced by quantum interference in a linear system consisting of a high-quality optical cavity and two coherently driven two-level qubits. When two qubits are placed in the cavity with a distance of integer multiple and one-half of wavelengths (i.e., they have the opposite coupling coefficient to the cavity), we show that squeezed light is generated in the hyperradiance regime under the conditions of strong coupling and weak driving. Simultaneously, Klyshko's criterion alternates up and down at unity when the photon number is even or odd. Moreover, the orthogonal angles of the squeezed light can be controlled by adjusting the frequency detuning between the driving field and the qubits. It can be implemented in a variety of quantum systems, including but not limited to two-level systems such as atoms, ions, quantum dots in single-mode cavities.

Tunable exciton-polaritons emerging from WS2 monolayer excitons in a photonic lattice at room temperature

Engineering non-linear hybrid light-matter states in tailored lattices is a central research strategy for the simulation of complex Hamiltonians. Excitons in atomically thin crystals are an ideal active medium for such purposes, since they couple strongly with light and bear the potential to harness giant non-linearities and interactions while presenting a simple sample-processing and room temperature operability. We demonstrate lattice polaritons, based on an open, high-quality optical cavity, with an imprinted photonic lattice strongly coupled to excitons in a WS2 monolayer. We experimentally observe the emergence of the canonical band-structure of particles in a one-dimensional lattice at room temperature, and demonstrate frequency reconfigurability over a spectral window exceeding 85 meV, as well as the systematic variation of the nearest-neighbour coupling, reflected by a tunability in the bandwidth of the p-band polaritons by 7 meV. The technology presented in this work is a critical demonstration towards reconfigurable photonic emulators operated with non-linear photonic fluids, offering a simple experimental implementation and working at ambient conditions.

Biaxially strained germanium crossbeam with a high-quality optical cavity for on-chip laser applications.

The creation of CMOS compatible light sources is an important step for the realization of electronic-photonic integrated circuits. An efficient CMOS-compatible light source is considered the final missing component towards achieving this goal. In this work, we present a novel crossbeam structure with an embedded optical cavity that allows both a relatively high and fairly uniform biaxial strain of ∼0.9% in addition to a high-quality factor of >4,000 simultaneously. The induced biaxial strain in the crossbeam structure can be conveniently tuned by varying geometrical factors that can be defined by conventional lithography. Comprehensive photoluminescence measurements and analyses confirmed that optical gain can be significantly improved via the combined effect of low temperature and high strain, which is supported by a three-fold reduction of the full width at half maximum of a cavity resonance at ∼1,940 nm. Our demonstration opens up the possibility of further improving the performance of germanium lasers by harnessing geometrically amplified biaxial strain.

Smooth GaN membranes by polarization-assisted electrochemical etching

III-nitride membranes offer promising perspectives and improved device designs in photonics, electronics, and optomechanics. However, the removal of the growth substrate often leads to a rough membrane surface, which increases scattering losses in optical devices. In this work, we demonstrate membranes with etched surface roughness comparable to that of the as-grown epitaxial material, accomplished by the implementation of a properly designed built-in polarization field near the top of the sacrificial layer from an AlInN interlayer, which is polarization-mismatched to GaN. This leads to a steeper reduction in free carrier density during the electrochemical etching of the sacrificial layer, limiting the etching current and thus causing an abrupter etch stop. As a result, the root mean square roughness is reduced to 0.4 nm over 5 × 5 μm2. These smooth membranes open attractive pathways for the fabrication of high-quality optical cavities and waveguides operating in the ultraviolet and visible spectral regions.

Photo-Triggered Logic Circuits Assembled on Integrated Illuminants and Resonant Nanowires

High-performance photo-triggered electronic devices have already become an abiding target of optoelectronics. Current results, involving high-sensitivity phototransistors with the enhancement of material properties or the modification of electrical field, need an independent external light-source system. Nevertheless, few research studies inform of circuits in which the logic channel can be directly light controlled by a fully integrated photogate. In this paper, nanowire-based photon-effect transistors (PETs) combined with organic light-emitting diode (OLED) gates, and the photo-triggered nanowire circuits (PTNCs) are exhibited. The nanowire channels are manifested as high-quality optical cavities coupled by reflective electrodes for forming standing wave resonance. With the function of resonance, the nanowire channel under the illumination of the OLED gate can reach a high on/off ratio of ∼107, and under the different interconnected configuration of OLED gates, the functions of PETs can separately be realized as P-type and N-type of CMOS-like transistors. Then, a PTNC inverter that includes two nanowire channels with the respective OLED gates is operated utilizing electrical input voltage and logic opposite output signal. NAND and NOR gates as PTNC have also been demonstrated and indicate their corresponding outstanding arithmetic logic operation. PTNCs can effectively represent an innovative step toward multipurpose photonic circuits as to programmable logic components and photo-triggered computing.

Excitonic Lasers in Atomically Thin 2D Semiconductors

Two-dimensional (2D) atomically thin transition-metal dichalcogenides (TMD) and their van der Waals (vdW) heterostructures offer a platform with tightly bound intralayer/interlayer excitons for the on-chip fabrication of ultracompact nanolasers. Excitons in 2D TMD materials present a considerable binding energy of up to hundreds of meV, which permits a high Mott transition density of 1014 cm–2 and stable excitonic lasing under room-temperature operation and high pump fluences. Here, we review the recent progress on the lasing emission from intralayer excitons in TMD monolayers and interlayer excitons in vdW heterostructures incorporated with various high-quality optical cavities, including photonic-crystal, whispering-gallery-mode, distributed-feedback, distributed-Bragg-reflector cavities. Lasing emissions in TMD monolayers and heterostructures have been demonstrated by narrow emission peaks, a clear threshold for nonlinear amplification, time- and spatial coherence under either continuous-wave or pulsed light pumping. Finally, prospective and frontier research topics, including large-scale on-chip integration of TMD nanolasers, electrically pumped lasers, spin-polarized nanolasers, and exciton–polariton Bose–Einstein condensation (BEC) are highlighted.

Polariton Microlasers: Multiphoton‐Pumped Highly Polarized Polariton Microlasers from Single Crystals of a Dye‐Coordinated Metal–Organic Framework (Adv. Funct. Mater. 32/2020)

In article number 2003294, Wei Ji and co-workers introduce an archetypical polariton laser, for the first time, based on single-crystalline metal-organic framework microplates, which possess the potential to be titled “next-generation laser.” The discovery of polariton lasing from bare metal-organic framework microplates, without the need to be embedded in a high-quality optical cavity, eliminates all fabrication complexities usually involved in realizing polaritons.

Lasing operation in the CsPbBr3 perovskite micron hemisphere cavity grown by chemical vapor deposition

Obtaining whispering gallery mode (WGM) lasing with prominent stability and high quality optical cavities is extremely desirable but still a great challenge. Despite the recent surge of reports on microspheres, nanowires and nanoplatelets metal halide crystals, there has few reports on the morphology of Hemispheres (HSs) in the form of uniform, component-tunable microcrystals. Here, CsPbX3 (X = Cl/Br) HSs with smooth surface and regular geometry structure were synthesized on silicon substrates by chemical vapor deposition (CVD) method, and the wavelength of laser can be continuously tuned from blue to green (450–540 nm) at room temperature by varying the halide composition. WGM laser with polarization ratio of 0.70 and cavity quality factor Q of 2485 were realized in the CsPbBr3 HS cavity. Besides, the crystal cavity suggested a high photonic and thermal stability for the superb capability of continuous stable lasing output under ambient conditions. All these results illustrate that the synthesis of cesium lead halide perovskite HSs may provide an alternative solution for fundamental researches and applications in optical devices.

Optical detection and storage of entanglement in plasmonically coupled quantum-dot qubits

Recent proposals and advances in quantum simulations, quantum cryptography and quantum communications substantially rely on quantum entanglement formation. Contrary to the conventional wisdom that dissipation destroys quantum coherence, coupling with a dissipative environment can also generate entanglement. We consider a system composed of two quantum dot qubits coupled with a common, damped surface plasmon mode; each quantum dot is also coupled to a separate photonic cavity mode. Cavity quantum electrodynamics calculations show that upon optical excitation by a femtosecond laser pulse, entanglement of the quantum dot excitons occurs, and the time evolution of the $g^{(2)}$ pair correlation function of the cavity photons is an indicator of the entanglement. We also show that the degree of entanglement is conserved during the time evolution of the system. Furthermore, if coupling of the photonic cavity and quantum dot modes is large enough, the quantum dot entanglement can be transferred to the cavity modes to increase the overall entanglement lifetime. This latter phenomenon can be viewed as a signature of entangled, long-lived quantum dot exciton-polariton formation. The preservation of total entanglement in the strong coupling limit of the cavity/quantum dot interactions suggests a novel means of entanglement storage and manipulation in high-quality optical cavities.

Optomechanical state reconstruction and nonclassicality verification beyond the resolved-sideband regime

Quantum optomechanics uses optical means to generate and manipulate quantum states of motion of mechanical resonators. This provides an intriguing platform for the study of fundamental physics and the development of novel quantum devices. Yet, the challenge of reconstructing and verifying the quantum state of mechanical systems has remained a major roadblock in the field. Here, we present a novel approach that allows for tomographic reconstruction of the quantum state of a mechanical system without the need for extremely high quality optical cavities. We show that, without relying on the usual state transfer presumption between light an mechanics, the full optomechanical Hamiltonian can be exploited to imprint mechanical tomograms on a strong optical coherent pulse, which can then be read out using well-established techniques. Furthermore, with only a small number of measurements, our method can be used to witness nonclassical features of mechanical systems without requiring full tomography. By relaxing the experimental requirements, our technique thus opens a feasible route towards verifying the quantum state of mechanical resonators and their nonclassical behaviour in a wide range of optomechanical systems.

Multiorder Stimulated Raman Scattering in Colliding Droplets.

Nonlinear Raman spectroscopy is a versatile method to enhance the intensities of Raman scattering. It requires an intense light field that can be provided by a liquid droplet acting as a high-quality optical cavity. Here, colliding droplets were used as a novel optical cavity to enhance the intensity of Raman scattering. Specifically, multiorder stimulated Raman-scattered light was generated with significant intensity from colliding droplets of carbon tetrachloride (CCl4). The intensities of the Raman bands were analyzed with a simple theory that roughly reproduced the experimental spectrum. Overall, the method facilitates Raman spectroscopy of molecules in liquids because of its high sensitivity and resolution.

Building up to superradiance, one by one

Quantum Optics Superradiance is a quantum phenomenon that occurs when emitters are sufficiently close to change spontaneous emission. Controlling the position and state of emitters within an atomic ensemble, however, is technically challenging. Kim et al. show that spatial correlations can be replaced by temporal correlations to achieve superradiance (see the Perspective by Meschede). They dropped prepared atoms into a high-quality optical cavity and found that the number of photons within the cavity built up superradiantly as the atoms dropped through one by one. The method provides a versatile platform for generating nonclassical states of light. Science , this issue p. [662][1]; see also p. [641][2] [1]: /lookup/volpage/359/662?iss=6376 [2]: /lookup/volpage/359/641?iss=6376

Coherent single-atom superradiance.

Superradiance is a quantum phenomenon emerging in macroscopic systems whereby correlated single atoms cooperatively emit photons. Demonstration of controlled collective atom-field interactions has resulted from the ability to directly imprint correlations with an atomic ensemble. Here we report cavity-mediated coherent single-atom superradiance: Single atoms with predefined correlation traverse a high-quality factor cavity one by one, emitting photons cooperatively with the N atoms that have already gone through the cavity (N represents the number of atoms). Enhanced collective photoemission of N-squared dependence was observed even when the intracavity atom number was less than unity. The correlation among single atoms was achieved by nanometer-precision position control and phase-aligned state manipulation of atoms by using a nanohole-array aperture. Our results demonstrate a platform for phase-controlled atom-field interactions.

Fabrication of High-Q Nanobeam Photonic Crystals in Epitaxially Grown 4H-SiC.

Silicon carbide (SiC) is an intriguing material due to the presence of spin-active point defects in several polytypes, including 4H-SiC. For many quantum information and sensing applications involving such point defects, it is important to couple their emission to high quality optical cavities. Here we present the fabrication of 1D nanobeam photonic crystal cavities (PCC) in 4H-SiC using a dopant-selective etch to undercut a homoepitaxially grown epilayer of p-type 4H-SiC. These are the first PCCs demonstrated in 4H-SiC and show high quality factors (Q) of up to ∼7000 as well as low modal volumes of <0.5 (λ/n)(3). We take advantage of the high device yield of this fabrication method to characterize hundreds of devices and determine which PCC geometries are optimal. Additionally, we demonstrate two methods to tune the resonant wavelengths of the PCCs over 5 nm without significant degradation of the Q. Lastly, we characterize nanobeam PCCs coupled to luminescence from silicon vacancy point defects (V1, V2) in 4H-SiC. The fundamental modes of two such PCCs are tuned into spectral overlap with the zero phonon line (ZPL) of the V2 center, resulting in an intensity increase of up to 3-fold. These results are important steps on the path to developing 4H-SiC as a platform for quantum information and sensing.

Quantum Phase Transition of Bose Einstein Condensation in Optical Cavity with Nonlinear Interaction

In this paper, we investigate the quantum phase transition of Bose-Einstein condensation in a high quality optical cavity with the atoms-cavity nonlinear interaction induced by the transverse pump light. Under the mean-field approximation, we give the phase diagram in the cases of both blue and red shifts. In the case of red shift, there exists momentum reversion phenomenon, in which the atomic occupation in the nonzero momentum state surpass that in the zero momentum state. Additionally, we reveal the spontaneous symmetry breaking mechanism in the system.

Interaction between light and highly confined hypersound in a silicon photonic nanowire

In the past decade, there has been a surge in research at the boundary between photonics and phononics. Most efforts centered on coupling light to motion in a high-quality optical cavity, typically geared towards observing the quantum state of a mechanical oscillator. It was recently predicted that the strength of the light-sound interaction would increase drastically in nanoscale silicon photonic wires. Here we demonstrate, for the first time, such a giant overlap between near-infrared light and gigahertz sound co-localized in a small-core silicon wire. The wire is supported by a tiny pillar to block the path for external phonon leakage, trapping $\mathbf{10} \; \textbf{GHz}$ phonons in an area below $\mathbf{0.1 \; \boldsymbol\mu}\textbf{m}^{\mathbf{2}}$. Since our geometry can be coiled up to form a ring cavity, it paves the way for complete fusion between the worlds of cavity optomechanics and Brillouin scattering. The result bodes well for the realization of low-footprint optically-pumped lasers/sasers and delay lines on a densely integrated silicon chip.

Analysis of the positional accuracy of the self-conjugate ray in a misalignment multiple-mirror optical ring cavity

In order to analyze the characteristic of the close optical axis (conjugate optical axis) and the existence condition of resonator composed of multiple reflective mirrors, the existence condition of conjugate optical axis of the multiple-resonator consisting of many flat mirrors is analyzed and derived from the angle of beam conversion coordinate transformation. The results show that a closed ray axis in resonator with odd number of mirrors can exist only if each mirror is suitably aligned, while a closed ray axis always exists in non-planar resonators with even number of mirrors, and the angle of the cavity conjugate axis direction changes due to the misalignment of different mirrors. Then from the point of view of the optical multi-pass matrix, the incidence direction of the self-conjugate ray of the resonator consisting of spherical mirrors is analyzed. A detailed analysis of conjugated axis of the resonator consisting of two flat mirrors and one spherical mirror is conducted, and the results show that when different mirrors have angle deviations, the closed conjugated optical axis remains in the cavity, the change of resonator axis occurs, and the position and orientation of new resonance surface are given, thereby indicating that in the case of resonator with spherical mirrors there is a self-conjugate ray irrespective of the other flat mirrors positions. All of these will provide theoretical guidance for achieving the high-accuracy alignment and improving the measurement accuracy of spectral measurement technology based on high-quality optical cavity.

Monolithic optofluidic ring resonator lasers created by femtosecond laser nanofabrication.

We designed, fabricated, and characterized a monolithically integrated optofluidic ring resonator laser that is mechanically, thermally, and chemically robust. The entire device, including the ring resonator channel and sample delivery microfluidics, was created in a block of fused-silica glass using a 3-dimensional femtosecond laser writing process. The gain medium, composed of Rhodamine 6G (R6G) dissolved in quinoline, was flowed through the ring resonator. Lasing was achieved at a pump threshold of approximately 15 μJ mm(-2). Detailed analysis shows that the Q-factor of the optofluidic ring resonator is 3.3 × 10(4), which is limited by both solvent absorption and scattering loss. In particular, a Q-factor resulting from the scattering loss can be as high as 4.2 × 10(4), suggesting the feasibility of using a femtosecond laser to create high quality optical cavities.