Cavity Mode Research Articles

Engineering Dispersive-Dissipative Modal Coupling in Hybrid Optical Microresonators.

Hybrid microresonators have served an intriguing platform for fundamental research and applied photonics. Here, we study the plasmonics-engineered coupling between degenerate optical whispering gallery modes, which can be tuned in a complex space featuring the dissipative strong, dispersive strong, and weak coupling regimes. Experimentally, the engineering of a single plasmonic resonance to a cavity mode family is examined in a waveguide-integrated high-Q microdisk, from which the complex coupling coefficients are extracted and agree well with theoretical predictions. The coupling strength over 10GHz is achieved for both dissipative and dispersive interactions, showing a remarkable enhancement compared to that induced by a dielectric scatterer. Furthermore, the far fields of hybridized cavity modes are measured, revealing the coherent interference between the radiative channels. Our results shed light on the engineering of whispering gallery modes through plasmonic resonances, and provide fundamental guidance to practical microcavity devices.

Strong coupling-induced frequency shifts of highly detuned photonic modes in multimode cavities.

Strong coupling between light and molecules is a fascinating topic exploring the implications of the hybridization of photonic and molecular states. For example, many recent experiments have explored the possibility that strong coupling of photonic and vibrational modes might modify chemical reaction rates. In these experiments, reactants are introduced into a planar cavity, and the vibrational mode of a chemical bond strongly couples to one of the many photonic modes supported by the cavity. Some experiments quantify reaction rates by tracking the spectral shift of higher-order cavity modes that are highly detuned from the vibrational mode of the reactant. Here, we show that the spectral position of these cavity modes, even though they are highly detuned, can still be influenced by strong coupling. We highlight the need to consider this strong coupling-induced frequency shift of cavity modes if one is to avoid underestimating cavity-induced reaction rate changes. We anticipate that our work will assist in the re-analysis of several high-profile results and has implications for the design of future strong coupling experiments.

Multiple hybrid Spp-Tamm modes in Ag grating/DBR microcavity

High confinement of surface plasmon polariton (SPP) have important applications in many aspects. However, access to high-Q resonant modes in metal cavity have many difficulties because of high Ohmic losses, large radiative losses and limited cavity designs. The Tamm mode is another surface plasmonic mode which has a high Q value but poor confinement. Here, we present a grating Tamm structure in which both nonradiative and radiative damping are suppressed, enabling excitation of high-Q and high confinement of hybrid SPP-Tamm mode. Theoretical analysis and simulations show that the proposed structure supports six resonance modes. By manipulating the geometric parameters of the metal grating, the multiple hybrid SPP-Tamm resonances could be well-defined and tuned with wavelength tuning sensitivity up to 1 nm. These results are promising for potential applications such as multiplexing, multi-frequency sensing and imaging.

Entanglement enhancement through magnon squeezing and optical parametric amplifier in cavity magnomechanics

We consider a cavity magnomechanical (CMM) system comprising magnon, cavity, and phonon modes. The coupling between the magnon and cavity, as well as between magnon and phonon, is mediated by the magnetic-dipole interaction and magnetostrictive interaction, respectively. By incorporating the optical parametric amplifier (OPA) and magnon squeezing mechanisms induced by the magnon self-Kerr nonlinearity, we observe a significant enhancement in entanglement between magnon-cavity, cavity-phonon, as well as tripartite entanglement, compared to the case where OPA and magnon squeezing are not introduced. We also explore the adverse effect of the thermal bath on the mechanical mode, specifically concerning the generation of magnon–phonon entanglement. Additionally, the presence of both magnon squeezing and OPA has been shown to play a crucial role in enhancing the robustness of entanglement against thermal effects compared to the cases when OPA is applied alone or when magnon squeezing is used alone. Here, the entanglement between the magnon and cavity persists up to a temperature of 284 mK, higher than previously observed values. The current CMM system shows promise for use in quantum tasks where it is necessary to enhance entanglement.

Fano resonance in one-dimensional quasiperiodic topological phononic crystals towards a stable and high-performance sensing tool

Phononic crystals (PnCs) emerge as an innovative sensor technology, especially for high-performance sensing applications. This study strives to advance this field by developing new designs of PnC structures that exhibit stability in the face of construction imperfections and deformations, focusing on the evolution of topological PnCs (TPnCs). These designs could be promising to overcome the problem of instability involved in most of the theoretical PnC sensors when they emerge in experimental verification. In particular, the fabrication process of any design could collide with some fluctuations in controlling the size of each component. Thus, Fano resonance is introduced through a one-dimensional (1D) quasiperiodic TPnC. To the best of the author’s knowledge, this study is the first to observe Fano modes in liquid cavities through 1D PnCs. Various quasiperiodic PnC designs are employed to detect the temperature of alcohols (specifically propanol) across an extensive temperature range (160–240 °C). The effects of many geometrical parameters on the sensor stability, such as material thicknesses, are studied. Numerical findings demonstrated that the designed quasiperiodic topological PnCs based on Fibonacci sequence of the second order proved superior performance. This sensing tool provides sensitivity, quality factor and figure-of-merit values of 104,533.33 Hz/°C, 223.69 and 0.5221 (/°C), respectively, through temperature detection of propanol in the range of 160–240 °C.

Photon Blockade in Cavity Optomechanics Via Parametric Amplification

AbstractPhoton blockade is a quantum phenomenon in driven nonlinear systems. It can be observed in cavity optomechanical systems when nonlinear optomechanical interaction occurs at the single‐photon level. However, achieving photon blockade in experiments is challenging due to the small single‐photon optomechanical coupling strength. Here, photon blockade in an optomechanical system is investigated, where the cavity mode is either strongly or weakly squeezed. When the cavity mode is strongly squeezed, the coupling between squeezed mode and mechanical mode will be exponentially enhanced, leading to strong optical nonlinearity that is required for the realization of photon blockade. In contrast, when the cavity mode is weakly squeezed, the nonlinear optomechanical interaction is weak. It is shown that photon blockade can also be realized through the destructive interference of two paths for two‐photon excitation. Interestingly, it is found that a larger mechanical decay rate facilitates the implementation of the interference‐based photon blockade, and thermal noise effects can be significantly suppressed by the destructive interference.

Influence of Quadrupolar Molecular Transitions within Plasmonic Cavities.

Optical nanocavities have revolutionized the manipulation of radiative properties of molecular and semiconductor emitters. Here, we investigate the amplified photoluminescence arising from exciting a dark transition of β-carotene molecules embedded within plasmonic nanocavities. Integrating a molecular monolayer into nanoparticle-on-mirror nanostructures unveils enhancements surpassing 4 orders of magnitude in the initially light-forbidden excitation. Such pronounced enhancements transcend conventional dipolar mechanisms, underscoring the presence of alternative enhancement pathways. Notably, Fourier-plane scattering spectroscopy shows that the photoluminescence excitation resonance aligns with a higher-order plasmonic cavity mode, which supports strong field gradients. Combining quantum chemistry calculations with electromagnetic simulations reveals an important interplay between the Franck-Condon quadrupole and Herzberg-Teller dipole contributions in governing the absorption characteristics of this dark transition. In contrast to free space, the quadrupole moment plays a significant role in photoluminescence enhancement within nanoparticle-on-mirror cavities. These findings provide an approach to access optically inactive transitions, promising advancements in spectroscopy and sensing applications.

High‐Speed and Low‐Power 2 × 2 Thermo‐Optic Switch Based on Dual Silicon Topological Nanobeam Cavities

AbstractA 2 × 2 thermo‐optic (TO) switch using dual topological photonic crystal nanobeam (PCN) cavities on the silicon‐on‐insulator (SOI) platform is proposed and experimentally demonstrated. A Fano resonance is observed due to the interference between the topological interface state of the 1D topological PCN cavity and the Fabry‐Perot (F‐P) cavity mode formed between the two facets of the finitely long nanobeam waveguide. Thanks to the sharp rising edge of the spectral response of the Fano resonance and the high confinement of light in the topological PCN cavities, a 2 × 2 TO switch is realized with short switching time and low power consumption. The measured switching power is only 1.55 mW, and the rising time and the falling time are 3 and 5.6 µs, respectively in the on‐off switching experiments. To the best of the knowledge, this is the first time that a dual topological PCN structure is utilized to realize a high‐speed and low‐power TO switch, revealing the possibility of designing high‐performance reconfigurable optical devices and networks using topological photonics.

Light-induced electron dynamics of molecules in cavities: comparison of model Hamiltonians

The rapidly expanding field of polaritonic chemistry requires accurate theoretical simulations to understand new phenomena at the atomic scale. Computing the optoelectronic properties of molecules using established electronic structure methods is a careful balance of accuracy and computational expense, and expanding these methods to quantum electrodynamics to describe coupled cavity-molecule systems is an active topic of development. Key to these methods are the Hamiltonian operators representing the photon cavity modes. The recently introduced quantum electrodynamics time-dependent configuration interaction (QED-TDCI) method allows for the combination of electron dynamics simulations with quantum electrodynamics, enabling the simulation of time-dependent optoelectronic properties of cavity-molecule systems. Using this method, a comparison of two many-state QED Hamiltonians—the Pauli-Fierz and quantum Rabi model Hamiltonians—is presented, with a particular focus on time-dependent properties in applied electric fields.

Strong coupling of Fabry-Pérot cavity mode, anapole, and exciton supported by an optical cavity with heterogeneous nano-optical metasurfaces

Strong coupling of Fabry-Pérot cavity mode, anapole, and exciton supported by an optical cavity with heterogeneous nano-optical metasurfaces

Highly tunable quasi-bound states in the continuum responses in subwavelength plasmonic-dielectric hybrid nanostructures

Here, we study the quasi-bound states in the continuum (Q-BIC) response in subwavelength hybrid nanostructures consisting of plasmonic antennas and subwavelength dielectric cavities. Among them, the plasmonic antennas are metal nanorods with electric dipole resonances, and the dielectric cavity is a nanodisk with an anapole mode. By reasonably adjusting the phase difference between the two modes, we can excite Q-BIC mode in the hybrid cavity. As the two modes involved in the construction of Q-BIC are on two separate structures, the Q-BIC of this hybrid nanostructure has great adjustability, and the quality factor of resonant mode can be increased several times. Our research enriches the generations of Q-BIC mode in subwavelength cavities, which may help to enhance light-matter interaction.

Band flipping and bandgap closing in a photonic crystal ring and its applications

The size of the bandgap in a photonic crystal ring is typically intuitively considered to monotonically grow as the modulation amplitude of the grating increases, causing increasingly large frequency splittings between the "dielectric" and "air" bands. In contrast, here we report that as the modulation amplitude in a photonic crystal ring increases, the bandgap does not simply increase monotonically. Instead, after the initial increase, the bandgap closes and then reopens again with the two bands flipped in energy. The air and dielectric band edges are degenerate at the bandgap closing point. We demonstrate this behavior experimentally in silicon nitride photonic crystal microrings, where we show that the bandgap is closed to within the linewidth of the optical cavity mode, whose intrinsic quality factor remains unperturbed with a value ≈ 1×106. Moreover, through finite-element simulations, we show that such bandgap closing and band flipping phenomena exist in a variety of photonic crystal rings with varying unit cell geometries and cladding layers. At the bandgap closing point, the two standing wave modes with a degenerate frequency are particularly promising for single-frequency lasing applications. Along this line, we propose a compact self-injection locking scheme that integrates many core functionalities in one photonic crystal ring. Additionally, the single-frequency lasing might be applicable to distributed-feedback (DFB) lasers to increase their manufacturing yield.

Entanglement and quantum coherence of two YIG spheres in a hybrid Laguerre–Gaussian cavity optomechanics

We theoretically investigate continuous variable entanglement and macroscopic quantum coherence in the hybrid L–G rotational cavity optomechanical system containing two YIG spheres. In this system, a single L–G cavity mode and both magnon modes (which are due to the collective excitation of spins in two YIG spheres) are coupled through the magnetic dipole interaction whereas the L–G cavity mode can also exchange orbital angular momentum (OAM) with the rotating mirror (RM). We study in detail the effects of various physical parameters like cavity and both magnon detunings, environment temperature, optorotational and magnon coupling strengths on the bipartite entanglement and the macroscopic quantum coherence as well. We also explore parameter regimes to achieve maximum values for both of these quantum correlations. We also observed that the parameters regime for achieving maximum bipartite entanglement is completely different from macroscopic quantum coherence. So, our present study shall provide a method to control various nonclassical quantum correlations of macroscopic objects in the hybrid L–G rotational cavity optomechanical system and have potential applications in quantum sensing, quantum meteorology, and quantum information science.

Macroscopic entanglement between ferrimagnetic magnons and atoms via crossed optical cavities.

We consider a two-dimensional opto-magnomechanical (OMM) system including two optical cavity modes, a magnon mode, a phonon mode, and a collection of two-level atoms. We show how the stationary entanglement between two-level atoms and magnons can be achieved. The presence of two optical cavities leads the atom-magnon entanglement to be achieved in a wide parameter regime. Furthermore, it is shown that one optical cavity can get entangled with magnons, phonons, and the other optical cavity. The entanglement is robust against thermal noise. The work may find applications in building hybrid quantum networks and quantum information processing.

Efficient multimode Wigner tomography.

Advancements in quantum system lifetimes and control have enabled the creation of increasingly complex quantum states, such as those on multiple bosonic cavity modes. When characterizing these states, traditional tomography scales exponentially with the number of modes in both computational and experimental measurement requirement, which becomes prohibitive as the system size increases. Here, we implement a state reconstruction method whose sampling requirement instead scales polynomially with system size, and thus mode number, for states that can be represented within such a polynomial subspace. We demonstrate this improved scaling with Wigner tomography of multimode entangled W states of up to 4 modes on a 3D circuit quantum electrodynamics (cQED) system. This approach performs similarly in efficiency to existing matrix inversion methods for 2 modes, and demonstrates a noticeable improvement for 3 and 4 modes, with even greater theoretical gains at higher mode numbers.

Influence of the Experimental Setup on Electromagnetic Pulses in the VHF Band at Relativistic High-Power Laser Facilities

We present experimental results for the controlled mitigation of the electromagnetic pulses (EMPs) produced in the interactions of a 1 PW high-power 30 fs Ti:Sa laser VEGA-3 with solid-density targets transparent to laser-forward-accelerated relativistic electrons. This study aims at the band of very high frequencies (VHFs), i.e., those in the hundreds of MHz, which comprise the fundamental cavity modes of the rectangular VEGA-3 vacuum chamber. We demonstrate mode suppression by a tailoring of the laser-produced space charge distribution.

Understanding the cavity Born-Oppenheimer approximation.

Experiments have demonstrated that vibrational strong coupling between molecular vibrations and light modes can significantly change molecular properties, such as ground-state reactivity. Theoretical studies toward the origin of this exciting observation can roughly be divided into two categories, with studies based on Hamiltonians that simply couple a molecule to a cavity mode via its ground-state dipole moment on the one hand, and on the other hand ab initio calculations that self-consistently include the effect of the cavity mode on the electronic ground state within the cavity Born-Oppenheimer (CBO) approximation; these approaches are not equivalent. The CBO approach is more rigorous, but unfortunately it requires the rewriting of electronic-structure code, and its results may sometimes be hard to physically interpret. In this work, we exploit the relation between the two approaches and demonstrate on a real molecule (hydrogen fluoride) that for realistic coupling strengths, we can recover CBO energies and spectra to high accuracy using only out-of-cavity quantities from standard electronic-structure calculations. In doing so, we discover what thephysical effects underlying the CBO results are. Our methodology can aid in incorporating more possibly important features in models, play a pivotal role in demystifying CBO results, and provide a practical and efficient alternative to full CBO calculations.

Generation of stationary entanglement and quantum discord in an optomechanical system through three-level atoms

In this paper, we investigate the stationary entanglement and quantum discord between the cavity and mechanical oscillator mode of an optomechanical system whose cavity contains three-level atoms. We examine how sharing entanglement and correlations would be affected by increasing the level of atoms injected into the cavity. In particular, using the appropriate preference of injected atoms to the cavity and optical cavity detuning, we found the impact of atoms and couplings on the degree of steady-state entanglement and quantum discord. Consequently, the stationary entanglement and quantum discord together rise to a certain range of normalized detuning and atom injection levels. Furthermore, both entanglement and Gaussian quantum discord are enhanced when three-level atoms are present, and the maximum entanglement manifests closest to the ringing case. Moreover, we are aware that the system’s physical parameters affect the generation of stationary entanglement and quantum correlation. Therefore, these results may provide a platform for a valuable asset in the practical realization of continuous variable entanglement and quantum information processing.

Observation of Extraneous Axial Cavity Modes of a Single-Mode Solid-State Laser Using Ultrahigh-Contrast Fabry–Perot Interferometry

Extraneous axial optical cavity modes produced by a single-mode frequency-doubled neodymium-doped yttrium orthovanadate (Nd:YVO[Formula: see text]) laser were observed in spectra obtained via ultrahigh-contrast Fabry–Perot interferometry. These modes, which are much weaker than the primary axial mode emission, are separated by [Formula: see text] GHz and display decreasing intensity with increasing shift from the primary laser line and with increasing laser output power. The possible presence of such modes in target sample spectra necessitates that caution be used in the interpretation of spectral peaks in laser spectroscopy studies, particularly Brillouin light scattering experiments. This work also showcases the remarkable capabilities of modern multipass Fabry–Perot interferometry in the detection of exceedingly weak optical signals shifted in frequency by only a few gigahertz from the primary laser emission line.

Fully Quantum Simulation of Polaritonic Vibrational Spectra of Large Cavity-Molecule System.

The formation of molecular vibrational polaritons, arising from the interplay between molecular vibrations and infrared cavity modes, is a quantum phenomenon necessitating accurate quantum dynamical simulations. Here, we introduce the cavity vibrational self-consistent field/virtual state configuration interaction method, enabling quantum simulation of the vibrational spectra of many-molecule systems within the optical cavity. Focusing on the representative (H2O)21 system, we showcase this parameter-free quantum approach's ability to capture both linear and nonlinear vibrational spectral features. Our findings highlight the growing prominence of molecular couplings among OH stretches and bending excited bands with increased light-matter interaction, revealing distinctive nonlinear spectral features induced by vibrational strong coupling.