Cavity Photon Research Articles

Cavity-mediated electron hopping in disordered quantum Hall systems

We investigate the emergence of long-range electron hopping mediated by cavity vacuum fields in disordered quantum Hall systems. We show that the counter-rotating (anti-resonant) light-matter interaction produces an effective hopping between disordered eigenstates within the last occupied Landau band. The process involves a number of intermediate states equal to the Landau degeneracy: each of these states consists of a virtual cavity photon and an electron excited in the next Landau band with the same spin. We study such a cavity-mediated hopping mechanism in the dual presence of a random disordered potential and a wall potential near the edges, accounting for both paramagnetic coupling and diamagnetic renormalization. We determine the cavity-mediated scattering rates, showing the impact on both bulk and edge states. The effect for edge states is shown to increase when their energy approaches the disordered bulk band, while for higher energy the edge states become asymptotically free. We determine the scaling properties while increasing the Landau band degeneracy. Consequences on the quantum Hall physics and future perspectives are discussed.

Driven dissipative quantum dynamics in a cavity magnon-polariton system

The dynamics of arbitrary-order quantum correlations in a cavity magnon-polariton system are investigated based on the quantum master equation in the coherent state representation. The phenomena of Rabi-like oscillation and level repulsion of the average cavity-photon number agree remarkably well with existing experimental observations. The competing nature of coherent and incoherent components in these two cases is further revealed by the second-order quantum coherence of the cavity photons and magnons, which can be systematically tuned by the driving microwave and thermal bath. Our results demonstrate the rich higher-order quantum dynamics induced by magnetic light-matter interaction, and serve as an indispensable step toward exploring nonclassical states for cavity photons and magnons in quantum cavity magnonics.

Strong light-matter coupling for optical switching through the fluorescence and FRET control

Resonant interaction between excitonic transitions of molecules and localized electromagnetic field forms the hybrid polaritonic states. Tuneable microresonators may change the light-matter coupling strength and modulate them from weak to strong and ultra-strong coupling regimes. In this work we have realised strong coupling between the tuneable open-access cavity mode and the excitonic transitions in oligonucleotide-based molecular beacons with their terminus labelled with a pair of organic dye molecules demonstrating an efficient donor-to-acceptor Förster resonance energy transfer (FRET). We show that the predominant strong coupling of the cavity photon to the exciton transition in the donor dye molecule can lead to such a large an energy shift that the energy transfer from the acceptor exciton reservoir to the mainly donor lower polaritonic state can be achieved, thus yielding the chromophores’ donor–acceptor role reversal or “carnival effect”. The data show the possibility for confined electromagnetic fields to control and mediate polariton-assisted remote energy transfer. Obtained results open the avenues to quantum optical switching and other applications.

Acousto-optic cavity coupling in 2D phoxonic crystal with combined convex and concave holes

A two-dimensional cross-like phoxonic crystal (PxC) model is proposed, which exhibits simultaneously large complete photonic crystal (PtC) and phononic crystal (PnC) bandgaps. The most salient trait of the structure is the wide range of geometrical parameters compatible with large complete bandgaps. After geometrical optimization, photonic and phononic bandgaps with gap-to-midgap ratios of 11.5% and 90.7% are obtained, respectively. These values are close to the best topology-optimized reported values but are obtained with simple shapes compatible with nanoscale fabrication technology. These characteristics make the convex–concave topology a promising candidate for PxC devices. A cavity is then introduced by filling up one cross-like hole in the 7 × 7 super-cell. PtC and PnC bands with defects appear in the respective large complete bandgaps, confining phonons and photons in the same cavity. Acousto-optic (AO) coupling between photonic and phononic defect modes is further investigated by the finite element method, taking both photoelastic and moving interface mechanisms into consideration. The symmetries of both photonic and phononic modes play a dominant role in the coupling strength. Results show that the strongest linear coupling between a photonic transverse magnetic mode and phononic breathing mode is obtained due to the in-phase superposition in the x and y directions. A quadratic nonlinear coupling is observed when photonic modes are coupled with the phononic stretching mode due to the inverse superposition of x and y directions. Finally, the optomechanical coupling rates relative to zero-point motion are estimated.

Enhancement and flexible control of slow light in a magnon–photon coupling system with N cavities

We theoretically analyze the transmission characteristics of a magnon–photon coupling system with N cascaded microwave cavities. The influences of the magnon–photon coupling strength and cavity number on the transmission characteristics are the main focus of this research. With an increase in the cascaded cavity number, the slow light effect should be greatly enhanced. By changing the cavity lengths slightly in a staggered way, the group delay could be increased by an order of magnitude with a well guaranteed transmission amplitude. Group delay should be flexibly controlled because of the existence of magnon and the conversion of fast and slow light can be realized. Moreover, by properly adjusting the cavity length, we can control the frequency shifting of the output slow light and narrow the bandwidth of the output slow light, which can aid in the design of high-quality light-storage devices. We believe the results will have applications in the all-optical communications network.

Strong single-photon optomechanical coupling in a hybrid quantum system.

Engineering strong single-photon optomechanical couplings is crucial for optomechanical systems. Here, we propose a hybrid quantum system consisting of a nanobeam (phonons) coupled to a spin ensemble and a cavity (photons) to overcome it. Utilizing the critical property of the lower-branch polariton (LBP) formed by the ensemble-phonon interaction, the LBP-cavity coupling can be greatly enhanced by three orders magnitude of the original one, while the upper-branch polariton (UBP)-cavity coupling is fully suppressed. Our proposal breaks through the condition of the coupling strength less than the critical value in previous schemes using two harmonic oscillators. Also, strong Kerr effect can be induced in our proposal. This shows our proposed approach can be used to study quantum nonlinear and nonclassical effects in weakly coupled optomechanical systems.

Nonlinear level attraction of cavity axion polariton in antiferromagnetic topological insulator

Strong coupling between cavity photons and various excitations in condensed matters boosts the field of light-matter interaction and generates several exciting sub-fields, such as cavity optomechanics and cavity magnon polariton. Axion quasiparticles, emerging in topological insulators, were predicted to strongly couple with the light and generate the so-called axion polariton. Here, we demonstrate that there arises a gapless level attraction in cavity axion polariton of antiferromagnetic topological insulators, which originates from a nonlinear interaction between axion and the odd-order resonance of cavity. Such a novel level attraction is essentially different from conventional level attractions with the mechanism of either a linear coupling or a dissipation-mediated interaction, and also different from the level repulsion induced by the strong coupling in common polaritons. Our results reveal a new mechanism of level attractions, and open up new roads for exploring the axion polariton with cavity technologies. They have potential applications for quantum information and dark matter research.

Proposal for a continuous wave laser with linewidth well below the standard quantum limit

Due to their high coherence, lasers are ubiquitous tools in science. We show that by engineering the coupling between the gain medium and the laser cavity as well as the laser cavity and the output port, it is possible to eliminate most of the noise due to photons entering as well as leaving the laser cavity. Hence, it is possible to reduce the laser linewidth by a factor equal to the number of photons in the laser cavity below the standard quantum limit. We design and theoretically analyze a superconducting circuit that uses Josephson junctions, capacitors and inductors to implement a microwave laser, including the low-noise couplers that allow the design to surpass the standard quantum limit. Our proposal relies on the elements of superconducting quantum information, and thus is an example of how quantum engineering techniques can inspire us to re-imagine the limits of conventional quantum systems.

Charge sensitivity of a cavity-embedded Cooper pair transistor limited by single-photon shot noise

Using an operator scattering approach, we analyze the quantum dynamics of an ultrasensitive electrometer—a Cooper pair transistor embedded in a quarter-wave microwave cavity (cCPT). While the cCPT is inherently a tunable, strongly nonlinear system affording a diverse range of functionalities, we restrict our present analysis to a necessary first investigation of its linear charge sensing capabilities, limiting to low pump powers corresponding to an average cavity photon number of ≲1. Assuming realizable cCPT parameters [B. L. Brock et al., Phys. Rev. Applied 15, 044009 (2021)], and not including noise from the subsequent amplifier chain, we predict the fundamental, photon shot noise-limited charge sensitivity to be 0.12μe/Hz when the pumped cavity has an average of one photon and the cCPT is operated close to charge degeneracy. This is to be compared with a first reported charge sensitivity value of 14μe/Hz in the single-photon regime [B. L. Brock et al., arXiv:2102.05362 (2021)].

Dipolariton propagation in a van der Waals TMDC with Ψ-shaped channel guides and buffered channel branches

Using a computational approach based on the driven diffusion equation for dipolariton wave packets, we simulate the diffusive dynamics of dipolaritons in an optical microcavity embedded with a transition metal dichalcogenide (TMDC) heterogeneous bilayer encompassing a [Formula: see text]-shaped channel. By considering exciton-dipolaritons, which are a three-way superposition of direct excitons, indirect excitons and cavity photons, we are able to drive the dipolaritons in our system by the use of an electric voltage and investigate their diffusive properties. More precisely, we study the propagation of dipolaritons present in a MoSe2-WS2 heterostructure, where the dipolariton propagation is guided by a [Formula: see text]-shaped channel. We also consider the propagation of dipolaritons in the presence of a buffer in the [Formula: see text]-shaped channel and study resulting changes in efficiency. We introduce designs for optical routers at room-temperature as well as show that system parameters including driving forces of [Formula: see text] eV/mm and electric field angles of [Formula: see text] optimize the dipolariton redistribution efficiencies in our channel guide.

Magnomechanical phonon laser beyond the steady state

Phonon lasers, the mechanical analogs of optical lasers, have long been a subject of interest as they provide coherent sound waves. We numerically study a magnomechanical phonon laser that operates under a general continuous-wave pump. This system consists of a microwave cavity, a sphere of magnetic material (yttrium iron garnet), a microwave drive pump, and a uniform external bias magnetic field. A population inversion between the supermodes of the system leads to phonon laser action. We study the population inversion and the stimulated emission of phonons under various conditions, such as different drive pump powers and detunings. Unlike previous studies, our results show that the population inversion between the supermodes oscillates with time. Despite the oscillations of the population inversion, one can achieve relatively large stimulated phonon emission if the power of the drive pump is beyond a threshold. Moreover, the optimum operation occurs if the frequency of the drive field matches the frequencies of the cavity photons and magnons. Since it is highly tunable with low loss and has an extra degree of freedom provided by the constant magnetic field, it is possible to develop the system into an alternative to the optomechanical phonon lasers.

Motional narrowing, ballistic transport, and trapping of room-temperature exciton polaritons in an atomically-thin semiconductor

Monolayer transition metal dichalcogenide crystals (TMDCs) hold great promise for semiconductor optoelectronics because their bound electron-hole pairs (excitons) are stable at room temperature and interact strongly with light. When TMDCs are embedded in an optical microcavity, excitons can hybridise with cavity photons to form exciton polaritons, which inherit useful properties from their constituents. The ability to manipulate and trap polaritons on a microchip is critical for applications. Here, we create a non-trivial potential landscape for polaritons in monolayer WS2, and demonstrate their trapping and ballistic propagation across tens of micrometers. We show that the effects of dielectric disorder, which restrict the diffusion of WS2 excitons and broaden their spectral resonance, are dramatically reduced for polaritons, leading to motional narrowing and preserved partial coherence. Linewidth narrowing and coherence are further enhanced in the trap. Our results demonstrate the possibility of long-range dissipationless transport and efficient trapping of TMDC polaritons in ambient conditions.

Optical normal-mode-induced phonon-sideband splitting in the photon-blockade effect

We study the photon-blockade effect in a loop-coupled optomechanical system consisting of two cavity modes and one mechanical mode. Here, the mechanical mode is optomechanically coupled to the two cavity modes, which are coupled with each other via a photon-hopping interaction. By treating the photon-hopping interaction as a perturbation, we obtain the analytical results of the eigenvalues and eigenstates of the system in the subspaces associated with zero, one, and two photons. We find a phenomenon of optical normal-mode-induced phonon-sideband splitting in the photon-blockade effect by analytically and numerically calculating the second-order correlation functions of the two cavity modes. This work not only presents a method to choose optimal driving frequency for photon blockade by tuning the photon-hopping interaction, but also provides a means to characterize the normal-mode splitting with cavity photon statistics.

Cavity exciton polaritons in two-dimensional semiconductors from first principles

Two-dimensional (2D) semiconducting microcavity, where exciton-polaritons can be formed, constitues a promising setup for exploring and manipulating various regimes of light-matter interaction. Here, the coupling between 2D excitons and metallic cavity photons is studied by using first-principles propagator technique. The strength of exciton-photon coupling is characterised by its Rabi splitting to two exciton-polaritons, which can be tuned by cavity thickness. Maximum splitting of 128 meV is achieved in phosporene cavity, while remarkable value of about 440 meV is predicted in monolayer hBN device. The obtained Rabi splittings in WS$_2$ microcavity are in excellent agreement with the recent experiments. Present methodology can aid in predicting and proposing potential setups for trapping robust 2D exciton-polariton condensates.

Simulating Quantum Particles on a Lattice

A new quantum simulator uses microwave photons in a superconducting cavity to simulate particles on a lattice similar to those found in superconductors or atomic nuclei.

Defect Polaritons from First Principles.

Control over the optical properties of defects in solid-state materials is necessary for their application in quantum technologies. In this study, we demonstrate, from first principles, how to tune these properties via the formation of defect polaritons in an optical cavity. We show that the polaritonic splitting that shifts the absorption energy of the lower polariton is much higher than can be expected from a Jaynes-Cummings interaction. We also find that the absorption intensity of the lower polariton increases by several orders of magnitude, suggesting a possible route toward overcoming phonon-limited single-photon emission from defect centers. These findings are a result of an effective continuum of electronic transitions near the lowest-lying electronic transition that dramatically enhances the strength of the light-matter interaction. We expect our findings to spur experimental investigations of strong light-matter coupling between defect centers and cavity photons for applications in quantum technologies.

Coupling between quantum dots and photonic crystal cavities

<p indent="0mm">Cavity quantum electrodynamics studies the interaction between light and matter at the single quanta level, i.e., cavity photons and quantum emitters, which has widespread applications in quantum information processing and optical devices, such as lasers, solar cells and light-emitting diodes. To study cavity quantum electrodynamics, a quantum emitter with excellent quantum properties and a cavity with high quality factor and small mode volume are preferred. The coupling between self-assembled quantum dots and photonic crystal cavities has attracted broad attention due to the advanced semiconductor fabrication techniques and excellent optical properties. Great progress has been made in the last two decades, which provides an efficient quantum interface between light and matter at the near-infrared domain. The self-assembled quantum dots have excellent optical properties, including high brightness, high single photon purity, and high indistinguishability, possessing great advantages in the applications of laser, single-photon source, entangled photon source and quantum bit. On the other hand, photonic crystal cavities have high quality factor and small mode volume, providing strong optical confinement. It can greatly enhance the interaction between light and matter. By coupling to photonic crystal cavities, the optical properties of quantum dots can be strongly modified. For example, in the weak coupling regime, where the coupling strength <italic>g</italic> is smaller than the decay rate of the system, the spontaneous emission rate of quantum dots is enhanced due to the increase of local density of states. The enhancement factor, known as Purcell factor, is proportional to the quality factor and inversely proportional to the mode volume of the cavity. The weak coupling can be used to optimize the performance of optical devices, such as reducing the laser threshold, increasing the efficiency of single-photon source and entangled photon source. In the strong coupling regime, where the coupling strength <italic>g</italic> is larger than the decay rate, the energy shifts back and forth between quantum dots and cavity modes at vacuum Rabi frequency, leading to the formation of exciton-polariton with Rabi splitting about 2<italic>g</italic>. The strong coupling has been widely proposed for the applications in quantum information processing and investigation of nonlinear optical effects at single photon level, such as the realization of quantum logical gate, the operation of qubit, the transfer of quantum states and single-photon blockade. Additionally, photonic crystal structures have a high level of integration. By integrating with waveguides, the coupled system, served as quantum nodes, can be connected to achieve the quantum internet. Besides the traditional photonic crystal cavities, recently a new type of cavity with topological origin has been proposed and demonstrated, providing a more robust platform to investigate cavity quantum electrodynamics and develop optical devices with built-in protection for topological nanophotonic circuitry. In this paper, we review the basic principle and recent progress of the coupling between self-assembled quantum dots and photonic crystal cavities, which show a great opportunity to realize various optical devices with diverse functionalities, providing an ideal platform to realize on-chip photonic circuitry.

Universal pair polaritons in a strongly interacting Fermi gas.

Cavity quantum electrodynamics (QED) manipulates the coupling of light with matter, and allows several emitters to couple coherently with one light mode1. However, even in a many-body system, the light-matter coupling mechanism has so far been restricted to one-body processes. Leveraging cavity QED for the quantum simulation of complex, many-body systems has thus far relied on multi-photon processes, scaling down the light-matter interaction to the low energy and slow time scales of the many-body problem2-5. Here we report cavity QED experiments using molecular transitions in a strongly interacting Fermi gas, directly coupling cavity photons to pairs of atoms. The interplay of strong light-matter and strong interparticle interactions leads to well-resolved pair polaritons-hybrid excitations coherently mixing photons, atom pairs and molecules. The dependence of the pair-polariton spectrum on interatomic interactions is universal, independent of the transition used, demonstrating a direct mapping between pair correlations in the ground state and the optical spectrum. This represents a magnification of many-body effects by two orders of magnitude in energy. In the dispersive regime, it enables fast, minimally destructive measurements of pair correlations, and opens the way to their measurement at the quantum limit and their coherent manipulation using dynamical, quantized optical fields.

Vectorial polaritons in the quantum motion of a levitated nanosphere

The strong coupling between elementary excitations of the electromagnetic field (photons) and quantized mechanical vibrations (phonons) produces hybrid quasi-particle states, known as phonon-polaritons. Their typical signature is the avoided crossing between the eigenfrequencies of the coupled system, as paradigmatically illustrated by the Jaynes-Cummings Hamiltonian, and observed in quantum electrodynamics experiments where cavity photons are coupled to atoms, ions, excitons, spin ensambles and superconducting qubits. In this work, we demonstrate the generation of phonon-polaritons in the quantum motion of an optically-levitated nanosphere. The particle is trapped in high vacuum by an optical tweezer and strongly coupled to a single cavity mode by coherent scattering of the tweezer photons. The two-dimensional motion splits into two nearly-degenerate components that, together with the optical cavity mode, define an optomechanical system with three degrees-of-freedom. As such, when entering the strong coupling regime, we observe hybrid light-mechanical states with a dispersion law typical of tripartite quantum systems. Remarkably, the independent components of motion here identify a physical vibration direction on a plane that, similarly to the polarization of light, confers a vectorial nature to the polariton field. Our results pave the way to novel protocols for quantum information transfer between photonic and phononic components and represent a key-step towards the demonstration of optomechanical entangled states at room temperature.

Parity-Symmetry-Protected Multiphoton Bundle Emission.

We demonstrate symmetry protected multiphoton bundle emission in the cavity QED system under the ultrastrong coupling regime. Our proposal only enables the super-Rabi oscillations with periodic generation of even correlated photons in the cavity, which is realized by combining the laser driven flip of qubit and the symmetry conserved transitions induced by Rabi interaction with parity symmetry. Combined with dissipation, only 2n-photon bundle emissions are allowed, due to the almost perfect suppression of bundle emissions with odd correlated photons. Meanwhile, the corresponding purities are significantly enhanced by the parity symmetry. This work extends multiphoton bundle emission to the ultrastrong coupling regime, and offers the prospect of exploring symmetry-protected multiphoton physics.