Photonic Cavity Modes Research Articles

Universal Quantum Optimization with Cold Atoms in an Optical Cavity.

Cold atoms in an optical cavity have been widely used for quantum simulations of many-body physics, where the quantum control capability has been advancing rapidly in recent years. Here, we show the atom cavity system is universal for quantum optimization with arbitrary connectivity. We consider a single-mode cavity and develop a Raman coupling scheme by which the engineered quantum Hamiltonian for atoms directly encodes number partition problems. The programmability is introduced by placing the atoms at different positions in the cavity with optical tweezers. The number partition problem solution is encoded in the ground state of atomic qubits coupled through a photonic cavity mode, which can be reached by adiabatic quantum computing. We construct an explicit mapping for the 3-SAT and vertex cover problems to be efficiently encoded by the cavity system, which costs linear overhead in the number of atomic qubits. The atom cavity encoding is further extended to quadratic unconstrained binary optimization problems. The encoding protocol is optimal in the cost of atom number scaling with the number of binary degrees of freedom of the computation problem. Our theory implies the atom cavity system is a promising quantum optimization platform searching for practical quantum advantage.

Design of an agile optical switcher based on a 1D silver plasmonic nanograting filled with a nonlinear Kerr material

In this paper, we investigate the nonlinear optical response characteristics of a metallic nanograting with nonlinear Kerr media within its slits using the finite element method. The proposed nanograting system is illuminated by a nanosecond Gaussian pulse laser under normal incidence and the electric filed pointing across the slits. The results show a perfect linear absorption at resonance wavelength thanks to the coupling of the surface plasmon resonance (SPR) mode and photon cavity mode. We simulate the transient nonlinear absorption variation of the system when the pulse laser is set up at either resonance or off-resonance wavelengths. The results indicate that the unit linear absorption drastically decreases by increasing the laser fluence around the center of the pulse. Interestingly, one can also enhance the weak linear off-resonance absorption to the value of unit by increasing the pulse laser fluence. The higher the laser fluence, the higher the maximum absorption contrast between linear and nonlinear regimes occurs owing to the nonlinear Kerr effect. Indeed, when the laser fluence reaches a critical value, it can excite the Kerr nonlinearity, which changes the coupling strength of SPR mode and the photon cavity mode leading to the absorption adjustment in the nanograting. These properties indicate the possibility of utilizing the proposed nanograting in dual functional absorber and nonabsorber systems, which make it an appropriate candidate for agile optical switching devices.

Acousto-optical coupling in two-dimensional air-slot phoxonic crystal heterostructure cavity

Phoxonic crystal is a periodic artificial structure that can manipulate optical and acoustic waves in the same temporal and spatial domain. It has broad application prospect in optical communication, optical mechanics sensor, quantum computations, phoxonic crystal integrated devices and so on. In this paper, we adopt a silicon-based two-dimensional square lattice structure, which can exhibit wide band gap of phonons and photons simultaneously. Then a periodic rectangular structure is introduced on the surface, the effects of the height and width of the rectangle on the optical and acoustic surface wave modes are analyzed. Based on the mode gap effect, a surface heterostructure composed of rectangles with different heights and widths is constructed. Then two identical surface heterostructures are placed face to face with an air slot in the middle, and connected with silicon substrate on both sides, which form an air slot heterostructure cavity. Five phononic cavity modes and three photonic cavity modes are obtained, the acousto-optical coupling rates between phononic and photonic cavity modes are calculated. The results show that the coupling rate between phononic and photonic cavity mode with the same symmetry and maximum overlap is the largest, and the coupling rates between the combination of phononic cavity modes α and β and photonic cavity modes can be adjusted by changing the phase difference φ of modes α and β. In this paper, the finite element method is used to simulate the calculation.

Nanostructured GaAs /( Al,Ga ) As Waveguide for Low-Density Polariton Condensation from a Bound State in the Continuum

Exciton-polaritons are hybrid light-matter states that arise from strong coupling between an exciton resonance and a photonic cavity mode. As bosonic excitations, they can undergo a phase transition to a condensed state that can emit coherent light without a population inversion. This aspect makes them good candidates for thresholdless lasers, yet short exciton-polariton lifetime has made it difficult to achieve condensation at very low power densities. In this sense, long-lived symmetry-protected states are excellent candidates to overcome the limitations that arise from the finite mirror reflectivity of monolithic microcavities. In this work we use a photonic symmetry-protected bound state in the continuum coupled to an excitonic resonance to achieve state-of-the-art polariton condensation threshold in a $\mathrm{Ga}\mathrm{As}$/($\mathrm{Al},\mathrm{Ga}$)$\mathrm{As}$ waveguide. Most important, we show the influence of fabrication control and how surface passivation via atomic layer deposition provides a way to reduce exciton quenching at the grating sidewalls.

Photonic cavity mode tuning in porous silicon-based microcavities by He+ and H+ ion irradiation

The present investigation reports the optical characteristics of the porous Si (PSi) based microcavities before and after energetic He+ and H+ ion irradiations. These PSi microcavities were fabricated by the galvanostatic electrochemical etching process and irradiated with 35 keV He+ and H+ ions with three different ion fluences: 1 × 1015, 5 × 1015, and 1 × 1016 ions/cm2. Significant color contrast is evident in the reflection images after ion irradiation. These reflection spectra of the optical microcavities are systematically investigated before and after ion irradiations. The dominant resonant cavity peak of the microcavity shows a notable shift of ∼28–48 and ∼17–26 nm toward the higher wavelength region with He+ and H+ ion irradiations at various ion fluences, respectively. The relative changes in the cavity wavelengths are about ∼5%–10% and ∼3%–5% for He+ and H+ ion irradiations, respectively. The redshift in the reflectance spectra is attributed to modification in the refractive index of microcavities induced by He+ and H+ ions. These experimental results compare well with the ion propagation and transfer matrix method simulations. The observed changes in the optical properties arise due to surface modification of the Si–Si and Si–O bonds and thereby refractive index modification of individual PSi layers of the microcavity. This study establishes that low-energetic ions produce broadly optically tunable and photonic structures suitable for optoelectronic applications.

High-Order Photonic Cavity Modes Enabled 3D Structural Colors.

It remains a challenge to directly print arbitrary three-dimensional shapes that exhibit structural colors at the micrometer scale. Woodpile photonic crystals (WPCs) fabricated via two-photon lithography (TPL) are elementary building blocks to produce 3D geometries that generate structural colors due to their ability to exhibit either omnidirectional or anisotropic photonic stop bands. However, existing approaches produce structural colors on WPCs when illuminating from the top, requiring print resolutions beyond the limit of commercial TPL, which necessitates postprocessing techniques. Here, we devised a strategy to support high-order photonic cavity modes upon side illumination on WPCs that surprisingly generate prominent reflectance peaks in the visible spectrum. Based on that, we demonstrate one-step printing of 3D photonic structural colors without requiring postprocessing or subwavelength features. Vivid colors with reflectance peaks exhibiting a full width at half-maximum of ∼25 nm, a maximum reflectance of 50%, a gamut of ∼85% of sRGB, and large viewing angles were achieved. In addition, we also demonstrated voxel-level manipulation and control of colors in arbitrary-shaped 3D objects constituted with WPCs as unit cells, which has potential for applications in dynamic color displays, colorimetric sensing, anti-counterfeiting, and light-matter interaction platforms.

Acousto-optical coupling of the side surface acoustic and optical waves in a two-dimensional phoxonic crystal slab hetero-structure cavity

Phoxonic crystal is a kind of artificial periodic structure which can manipulate light and sound in the same time and space domain. It has good application prospect in optical communication system and opto-mechnical sensor. In this paper, a two-dimensional silicon phoxonic crystal slab structure is proposed, which can exhibit large phononic and photonic bandgaps simultaneously. Then a periodic cylindrical structure is introduced on the side surface of the slab. The effects of the height and radius of the cylinder on the side surface wave modes are analyzed. On this basis, a phoxonic crystal hetero-structure cavity composed of cylinders with different radii and heights is constructed, which can simultaneously confine the acoustic and optical modes because of mode gap effect. Seven phononic cavity modes and two photonic cavity modes are obtained. The two photonic cavity modes are called dielectric mode and air mode respectively. Further, the acousto-optical coupling rates between the seven phononic cavity modes and dielectric mode are calculated. Finally, a gap is etched on each cylinder in hetero-structure cavity, which can increase the surface area of the cavity by 23%. Then two phononic cavity modes and photonic dielectric mode with higher coupling rates are considered. The results show that etching the z-direction gap in the center of the cylinder can effectively increase the acousto-optical coupling rates.

Effective mass of cavity-vibration polaritons formed in etalons with liquid carbon tetrachloride.

Etalons are pairs of parallel plate mirrors with wavelength-scale spacing that exhibit cavity modes, giving transmission maxima (fringes) due to constructive interference. Infrared transmission measurements as a function of angle were used to determine the effective mass of etalon cavity modes using a gap filled with air and then liquid carbon tetrachloride. The air-filled etalon gives results in agreement with pure photon expectations established herein. Liquids with vibrations having strong infrared transition intensity (vibrational strong coupling mode) can strongly perturb the pattern of transmission resonances, creating mixed states of infrared cavity modes and molecular vibrations, i.e., cavity-vibration polaritons. The effective mass of one cavity-vibration polariton close to the strong vibration of carbon tetrachloride is 4.36 times heavier than the pure photon cavity mode expectation, i.e., the mass factor vs pure light. The mass factors are largest when closest to the strong vibrational frequency, and they converge to the one far away from the strong vibration. This work gives quantitative values of the effective mass of cavity-vibration polariton states and is a diagnostic for the mixing of vibrations with etalon transmission.

Generalization of the Tavis–Cummings model for multi-level anharmonic systems

The interaction between anharmonic quantum emitters (e.g. molecular vibrations) and confined electromagnetic fields gives rise to quantum states with optical and chemical properties that are different from those of their precursors. The exploration of these properties has been typically constrained to the first excitation manifold, the harmonic approximation, ensembles of two-level systems [Tavis–Cummings (TC) model], or the anharmonic single-molecule case. The present work studies, for the first time, a collective ensemble of identical multi-level anharmonic emitters and their dipolar interaction with a photonic cavity mode, which is an exactly solvable many-body problem. The permutational properties of the system allow identifying symmetry classified submanifolds in the energy spectrum. Notably, in this approach, the number of particles, typically in the order of several millions, becomes only a parameter from the operational standpoint, and the size of the dimension of the matrices to diagonalize is independent of it. The formalism capabilities are illustrated by showing the energy spectrum structure, up to the third excitation manifold, and the calculation of the photon contents as a permutationally invariant quantity. Emphasis is placed on (a) the collective (superradiant) scalings of light–matter couplings and the various submanifolds of dark (subradiant) states with no counterpart in the single-molecule case, as well as (b) the delocalized modes containing more than one excitation per molecule with no equivalent in the TC model. We expect these findings to be applicable in the study of non-linear spectroscopy and chemistry of polaritons.

Entangled photon assisted multidimensional nonlinear optics of exciton–polaritons

We present a theoretical formulation of the frequency domain multidimensional pump-probe analog spectroscopy, which utilizes the spectral–temporal entanglement features of the biphoton sources. It has been shown, via a compact multi-time, convolutional Green’s function expression and the accompanying numerical simulations, that utilizing the correlation properties of non-classical sources offers a viable scheme for the exploration of dissipative kinetics of the cavity confined quantum aggregates. The cooperative and competitive modifications brought in by the photonic cavity mode and the auxiliary vibrational modes into the scattering and dephasing properties of the exciton–polaritons have been explored via their signatures in the multidimensional correlation maps. The study offers a new parameter window for the investigation of the dynamical polariton characteristics and warrants the usage of multi-mode entanglement properties of the external photonic sources in future studies.

Lithium niobate photonic-crystal electro-optic modulator

Modern advanced photonic integrated circuits require dense integration of high-speed electro-optic functional elements on a compact chip that consumes only moderate power. Energy efficiency, operation speed, and device dimension are thus crucial metrics underlying almost all current developments of photonic signal processing units. Recently, thin-film lithium niobate (LN) emerges as a promising platform for photonic integrated circuits. Here, we make an important step towards miniaturizing functional components on this platform, reporting high-speed LN electro-optic modulators, based upon photonic crystal nanobeam resonators. The devices exhibit a significant tuning efficiency up to 1.98 GHz V−1, a broad modulation bandwidth of 17.5 GHz, while with a tiny electro-optic modal volume of only 0.58 μm3. The modulators enable efficient electro-optic driving of high-Q photonic cavity modes in both adiabatic and non-adiabatic regimes, and allow us to achieve electro-optic switching at 11 Gb s−1 with a bit-switching energy as low as 22 fJ. The demonstration of energy efficient and high-speed electro-optic modulation at the wavelength scale paves a crucial foundation for realizing large-scale LN photonic integrated circuits that are of immense importance for broad applications in data communication, microwave photonics, and quantum photonics.

Thermal-stability resonators for visible light full-spectrum perfect absorbers

Perfect light absorption is desirable for applications in the devices related to photo-electrical effects, photo-thermal process and photo-chemical/catalysis solutions, etc. In this work, we propose and demonstrate a feasible way to achieve broadband perfect absorption in the full visible range based on the refractory material resonators. This structure shows excellent absorption efficiency with the average absorption up to 94% in the wavelength range from 380 nm to 760 nm (the visible region), suggesting the impressive capability of energy harvesting. The photonic cavity mode and the dipolar plasmon resonance by the half-cylinder cavity structure are the main contributions for the broadband absorption. The full-spectrum visible light absorption is observed to be maintained in a wide angle range under the oblique illumination. The high absorption is also retained under different polarization states. Moreover, the resonant materials such as titanium dioxide (TiO2) and titanium nitride (TiN) have impressive thermal stability due to their high melting points. These findings pave new insights on the refractory perfect visible light absorber for nano-scale photo-thermal process, micro-fluidic thermal disinfect and local high-temperature process, etc.

Plasmonic Surface Lattice Resonances: Theory and Computation.

Plasmonic surface lattice resonances (SLRs) are mixed light-matter states emergent in a system of periodically arranged metallic nanoparticles (NPs) under the constraint that the array spacing is able to support a standing wave of optical-frequency light. The properties of SLRs derive from two separate physical effects; the electromagnetic (plasmonic) response of metal NPs and the electromagnetic states (photonic cavity modes) associated with the array of NPs. Metal NPs, especially free-electron metals such as silver, gold, aluminum, and alkali metals, support optical-frequency electron density oscillations known as localized surface plasmons (LSPs). The high density of conduction-band electrons in these metals gives rise to plasmon excitations that strongly couple to light even for particles that are several orders of magnitude smaller than the wavelength of the excitation source. In this sense, LSPs have the remarkable ability to squeeze far-field light into intensely localized electric near-fields that can enhance the intensity of light by factors of ∼103 or more. Moreover, as a result of advances in the synthesis and fabrication of NPs, the intrinsic dependence of LSPs on the NP geometry, composition, and size can readily be exploited to design NPs with a wide range of optical properties. One drawback in using LSPs to enhance optical, electronic, or chemical processes is the losses introduced into the system by dephasing and Ohmic damping-an effect that must either be tolerated or mitigated. Plasmonic SLRs enable the mitigation of loss effects through the coupling of LSPs to diffractive states that arise from arrays satisfying Bragg scattering conditions, also known as Rayleigh anomalies. Bragg modes are well-known for arrays of dielectric NPs, where they funnel and trap incoming light into the plane of the lattice, defining a photonic cavity. The low losses and narrow linewidths associated with dielectric NPs produce Bragg modes that oscillate for ∼103-104 cycles before decaying. These modes are of great interest to the metamaterials community but have relatively weak electric fields associated with dielectric NPs and therefore are not used for applications where local field enhancements are needed. Plasmonic lattices, i.e., photonic crystals composed of metallic NPs, combine the characteristics of both LSPs and diffractive states, enabling both enhanced local fields and narrow-linewidth excitations, in many respects providing the best advantages of both materials. Thus, by control of the periodicity and global symmetry of the lattice in addition to the material composition and shape of the constituent NPs, SLRs can be designed to simultaneously survive for up to 103 cycles while maintaining the electric field enhancements near the NP surface that have made the use of LSPs ubiquitous in nanoscience. Modern fabrication methods allow for square-centimeter-scale patches of two-dimensional arrays that are composed of approximately one trillion NPs, making them effectively infinite at the nanoscale. Because of these advances, it is now possible to experimentally realize SLRs with properties that approach those predicted by idealized theoretical models. In this Account, we introduce the fundamental theory of both SLRs and SLR-mediated lasing, where the latter is one of the most important applications of plasmonic SLRs that has emerged to date. The focus of this Account is on theoretical concepts for describing plasmonic SLRs and computational methods used for their study, but throughout we emphasize physical insights provided by the theory that aid in making applications.

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.

CAVITY MODES IN DUAL PHONONIC AND PHOTONIC CRYSTAL WITH WIDE ABSOLUTE BANDGAP

In this paper, we discuss theoretically the simultaneous existence of dual phononic and photonic band gaps and cavity modes in a PhoXonic crystal. The cavity is created in the center of a square lattice PhoXonic crystal made from silicon using the one-missing-holes point defect (L1). Following the design, dispersion diagrams and the resonant frequency are numerically analyzed by the finite elements method (FEM). Optimization of the PhoXonic crystal design by modulating the structure parameter yields a complete phononic gap together with a photonic gap. Furthermore, we demonstrate the existence of the largest number of cavity modes with a high quality factor of 10 5 . This structure configuration design shows considerable promise as regards the simultaneous confinement of acoustic and optical waves and thus more attractive for experimental observation of optomechanical coupling.

Deterministic coupling of a system of multiple quantum dots to a single photonic cavity mode

We fabricated and studied a system comprising four site-controlled semiconductor quantum dots (QDs) embedded in a linear photonic crystal membrane cavity. The excellent position control and small spectral broadening permit coupling of the emission of all four QDs to the same photonic cavity modes. This is corroborated by co-polarization of the QD and cavity emission lines, as well as reduction in decay time, both with characteristic dependence on QD-cavity energy detuning. Scaling up to larger QD systems is discussed.

Influence of phonons on solid-state cavity-QED investigated using nonequilibrium Green's functions

The influence of electron-phonon interactions on the dynamics of a quantum dot coupled to a photonic cavity mode is investigated by using a nonequilibrium Green's function approach. Within a polaron frame, the self-consistent-Born approximation is used to treat the phonon-assisted scattering processes between the quantum dot polaron and the cavity. Two-time correlators of the quantum dot-cavity system are calculated by solving the Kadanoff--Baym equations, giving access to photon spectra and photon indistinguishability. The non-Markovian nature of the interaction with the phonon bath is shown to be very accurately described by our method in various regimes of cavity quantum electrodynamics (cavity-QED). The indistinguishability of the emitted photons emitted at zero temperature are found to be in very good agreement with a previously reported exact diagonalization approach [Phys. Rev. B 87, 081308 (2013)]. Besides, our method enables the calculations of photon indistinguishability at finite temperatures and for strong electron-phonon interactions. More generally, our method opens new avenues in the study of open quantum system dynamics coupled to non-Markovian environments.

Enhancement of acousto-optical coupling in two-dimensional air-slot phoxonic crystal cavities by utilizing surface acoustic waves

A phoxonic crystal is a periodically patterned material that can simultaneously localize optical and acoustic modes. The acousto-optical coupling in two-dimensional air-slot phoxonic crystal cavities is investigated numerically. The photons can be well confined in the slot owing to the large electric field discontinuity at the air/dielectric interfaces. Besides, the surface acoustic modes lead to the localization of the phonons near the air-slot. The high overlap of the photonic and phononic cavity modes near the slot results in a significant enhancement of the moving interface effect, and thus strengthens the total acousto-optical interaction. The results of two cavities with different slot widths show that the coupling strength is dependent on the slot width. It is expected to achieve a strong acousto-optical/optomechanical coupling in air-slot phoxonic crystal structures by utilizing surface acoustic modes.

Quantum statistics in a time-modulated exciton-photon system

We consider a system consisting of a large individual quantum dot with excitonic resonance coupled to a single mode photonic cavity in the nonlinear regime when exciton- exciton interaction becomes important. We show that in the presence of time-modulated external coherent pumping the system demonstrates essentially non classical behavior reflected in sub-Poissonian statistics of exciton- and photon-modes and the Wigner functions with negative values in phase-space for time-intervals exceeding the characteristic time of dissipative processes, $t\gg\gamma^{-1}$. It is shown that these results are cardinally different from the analogous results in the regime of the monomode continues-wave (cw) excitation.

Topological polaritons in a quantum spin Hall cavity

We study the topological structure of matter-light excitations, so called polaritons, in a quantum spin Hall insulator coupled to photonic cavity modes. We identify a topological invariant in the presence of time reversal (TR) symmetry, and demonstrate the existence of a TR-invariant topological phase. We find protected helical edge states with energies below the lower polariton branch and characteristic uncoupled excitonic states, both detectable by optical techniques. Applying a Zeeman field allows us to relate the topological index to the double coverage of the Bloch sphere by the polaritonic pseudospin.