Polariton States Research Articles

Observation of a hybrid state of Tamm plasmons and microcavity exciton polaritons.

We present evidence for the existence of a hybrid state of Tamm plasmons and microcavity exciton polaritons in a II-VI material based microcavity sample covered with an Ag metal layer. The bare cavity mode shows a characteristic anticrossing with the Tamm-plasmon mode, when microreflectivity measurements are performed for different detunings between the Tamm plasmon and the cavity mode. When the Tamm-plasmon mode is in resonance with the cavity polariton four hybrid eigenstates are observed due to the coupling of the cavity-photon mode, the Tamm-plasmon mode, and the heavy- and light-hole excitons. If the bare Tamm-plasmon mode is tuned, these resonances will exhibit three anticrossings. Experimental results are in good agreement with calculations based on the transfer matrix method as well as on the coupled-oscillators model. The lowest hybrid eigenstate is observed to be red shifted by about 13 meV with respect to the lower cavity polariton state when the Tamm plasmon is resonantly coupled with the cavity polariton. This spectral shift which is caused by the metal layer can be used to create a trapping potential channel for the polaritons. Such channels can guide the polariton propagation similar to one-dimensional polariton wires.

Efficient Radiative Pumping of Polaritons in a Strongly Coupled Microcavity by a Fluorescent Molecular Dye

The optical properties of a series of strongly coupled microcavities containing the fluorescent molecular dye BODIPY‐Br (bromine‐substituted boron‐dipyrromethene) dispersed into a transparent dielectric matrix are explored, with each cavity having a different exciton–photon detuning. Using temperature dependent emission, time‐resolved spectroscopy, white‐light reflectivity, and measurements of fluorescence quantum yield, the population of polaritons is explored along the lower polariton branch. It is found that both the cavity fluorescence quantum efficiency and the distribution of polariton states along the lower polariton branch is a function of exciton–photon detuning. Importantly, it is shown that in the most negatively detuned cavities, the emission quantum efficiency approaches that of a control (noncavity) film. A simple fitting model is developed, which is based upon direct radiative pumping of polariton states along the lower polariton branch and used it to obtain an excellent agreement with measured photoluminescence as a function of temperature and exciton–photon detuning, and qualitative agreement with the measured photoluminescence quantum efficiency. The radiative pumping mechanism indicates that to facilitate the formation of a nonequilibrium polariton condensate in strongly‐coupled microcavities containing dispersed molecular dyes, it is important to utilize materials having high fluorescent quantum efficiency and fast radiative rates.

Spatial self-organization of macroscopic quantum states of exciton-polaritons in acoustic lattices

Exciton-polariton systems can sustain macroscopic quantum states (MQSs) under a periodic potential modulation. In this paper, we investigate the structure of these states in acoustic square lattices by probing their wave functions in real and momentum spaces using spectral tomography. We show that the polariton MQSs, when excited by a Gaussian laser beam, self-organize in a concentric structure, consisting of a single, two-dimensional gap-soliton (GS) state surrounded by one dimensional (1D) MQSs with lower energy. The latter form at hyperbolical points of the modulated polariton dispersion. While the size of the GS tends to saturate with increasing particle density, the emission region of the surrounding 1D states increases. The existence of these MQSs in acoustic lattices is quantitatively supported by a theoretical model based on the variational solution of the Gross–Pitaevskii equation. The formation of the 1D states in a ring around the central GS is attributed to the energy gradient in this region, which reduces the overall symmetry of the lattice. The results broaden the experimental understanding of self-localized polariton states, which may prove relevant for functionalities exploiting solitonic objects.

Specific features of the hybridization of Frenkel and Wannier–Mott excitons in a microcavity

Polariton states have been investigated in a microcavity, where the energy of the Frenkel exciton in an organic quantum well and the energy of the semiconductor Wannier–Mott exciton in an inorganic quantum well are close to the microcavity optical mode. It has been shown that the interaction of each of these excitons with the microcavity optical mode leads to their interaction with each other and to the formation of mutually coupled hybrid excitations. The influence of the location of the quantum wells in a microcavity on the spectra of hybrid states with different polarizations has been analyzed.

Hyperbolic metamaterials based on Bragg polariton structures

A new hyperbolic metamaterial based on a modified semiconductor Bragg mirror structure with embedded periodically arranged quantum wells is proposed. It is shown that exciton polaritons in this material feature hyperbolic dispersion in the vicinity of the second photonic band gap. Exciton–photon interaction brings about resonant nonlinearity leading to the emergence of nontrivial topological polaritonic states. The formation of spatially localized breather-type structures (oscillons) representing kink-shaped solutions of the effective Ginzburg–Landau–Higgs equation slightly oscillating along one spatial direction is predicted.

Polariton states in circuit QED for electromagnetically induced transparency

Electromagnetically induced transparency (EIT) has been extensively studied in various systems. However, it is not easy to observe in superconducting quantum circuits (SQCs), because the Rabi frequency of the strong controlling field corresponding to EIT is limited by the decay rates of the SQCs. Here, we show that EIT can be achieved by engineering decay rates in a superconducting circuit QED system through a classical driving field on the qubit. Without such a driving field, the superconducting qubit and the cavity field are approximately decoupled in the large detuning regime, and thus the eigenstates of the system are approximately product states of the cavity field and qubit states. However, the driving field can strongly mix these product states and so-called polariton states can be formed. The weights of the states for the qubit and cavity field in the polariton states can be tuned by the driving field, and thus the decay rates of the polariton states can be changed. We choose a three-level system with $\Lambda$-type transitions in such a driven circuit QED system, and demonstrate how EIT and ATS can be realized in this compound system. We believe that this study will be helpful for EIT experiments using SQCs.

Perfect photon absorption in the nonlinear regime of cavity quantum electrodynamics

It has been shown that perfect photon absorption can occur in the linear excitation regime of cavity quantum electrodynamics (CQED), in which photons from two identical light fields coupled into two ends of the cavity are completely absorbed and result in excitation of the polariton state of the CQED system. The output light from the cavity is totally suppressed by the destructive interference and the polariton state can only decay incoherently back to the ground state. Here we analyze the perfect photon absorption and onset of optical bistability in the nonlinear regime of the CQED and show that the perfect photon absorption persists in the nonlinear regime of the CQED below the threshold of the optical bistability. Therefore the perfect photon absorption is a phenomenon that can be observed in both linear and nonlinear regimes of CQED. Furthermore, our study reveals for the first time that the optical bistability is influenced by the input-light interference and can be manipulated by varying the relative phase of the two input fields.

Topological polaritons with squeezed photons

In this paper, we demonstrate that the topological polaritonic states of a two-dimensional coupled matter–light system can be optically controlled. By introducing a squeezed light field, we generalized the model of topological polaritons, where the matter–light coupling constant winds in momentum space, leading to the nontrivial topology. The bulk excitation spectrum, polariton wave function, topological invariant, and edge mode spectrum are calculated. It is found that mixing the excitons with nonsqueezing photons will result in a time-reversal-symmetry-breaking quantum-spin-Hall-like polaritonic state. However, the quantum-Hall-like state arises when the photonic part of the polaritons is squeezed. Driven by the varying degree of squeezing, there is a topological phase transition with the closing of the bulk excitation gap. Across the phase transition, the direction of edge mode propagation is reversed, which is demonstrated by an edge mode simulation. Such a feature may provide an opportunity for realizing one-way edge channels with adjustable directionality.

Complete Coherent Control of a Quantum Dot Strongly Coupled to a Nanocavity.

Strongly coupled quantum dot-cavity systems provide a non-linear configuration of hybridized light-matter states with promising quantum-optical applications. Here, we investigate the coherent interaction between strong laser pulses and quantum dot-cavity polaritons. Resonant excitation of polaritonic states and their interaction with phonons allow us to observe coherent Rabi oscillations and Ramsey fringes. Furthermore, we demonstrate complete coherent control of a quantum dot-photonic crystal cavity based quantum-bit. By controlling the excitation power and phase in a two-pulse excitation scheme we achieve access to the full Bloch sphere. Quantum-optical simulations are in good agreement with our experiments and provide insight into the decoherence mechanisms.

Effect of barrier width on the exciton states in coupled quantum wells in an applied electric field

The effect of barrier width on the exciton states in coupled quantum wells has been theoretically studied using an efficient approach. By solving the Schrödinger equation in real space, the electron and hole energies and wave functions are calculated in the presence of an applied electric field. It is found that with zero electric field the energy splitting of the doublets is large in the case of thin barrier width. However for thicker barrier width, the Stark effect is stronger at large electric field. The exciton states, binding energies and oscillator strength are also calculated as a function of electric field. There is shown the direct-to-indirect crossover of the exciton ground state at approximately F=10 kV/cm and F=5 kV/cm for Lb=2 nm and Lb=4 nm respectively, corresponding to the dramatic decrease of its binding energy and oscillator strength. This direct-to-indirect crossover happens at lower electric field for thicker barrier width. We have also studied the light–matter coupling and calculated the DX, IX and CM components of the polariton states as a function of electric field.

Two-dimensional infrared spectroscopy of vibrational polaritons of molecules in an optical cavity

Strong coupling of molecular vibrations to an infrared cavity mode affects their nature by creating dressed polariton states. We show how the single and double vibrational polariton manifolds may be controlled by varying the cavity coupling strength and probed by a time domain two-dimensional infrared (2DIR) technique, double quantum coherence. Applications are made to the amide-I (CO) and amide-II (CN) bond vibrations of N-methylacetamide.

Entangling polaritons via dynamical Casimir effect in circuit quantum electrodynamics

We investigate how the dynamical Casimir effect can entangle quantum systems in different coupling regimes of circuit quantum electrodynamics, and show the robustness of such entanglement generation against dissipative effects with current technology. We consider two qubit-resonator systems, which are coupled by a SQUID driven with an external magnetic field, and explore the entire range of coupling regimes between each qubit and its respective resonator. In this scheme, we derive a semianalytic explanation for the entanglement generation between both superconducting qubits when they are coupled to their resonators in the strong coupling regime. For the ultrastrong and deep strong coupling regimes, we design feasible protocols to generate maximally-entangled polaritonic states.

Quantum-state transfer in staggered coupled-cavity arrays

We consider a coupled-cavity array, where each cavity interacts with an atom under the rotating-wave approximation. For a staggered pattern of intercavity couplings, a pair of field normal modes, each bilocalized at the two array ends, arises. A rich structure of dynamical regimes can hence be addressed, depending on which resonance condition is set between the atom and the field modes. We show that this can be harnessed to carry out high-fidelity quantum-state transfer (QST) of photonic, atomic, or polaritonic states. Moreover, by partitioning the array into coupled modules of shorter length, the QST time can be substantially shortened without significantly affecting the fidelity.

Quantum Symmetry Breaking of Exciton/Polaritons in a Metal-Nanorod Plasmonic Array.

We study the collective, superradiant behavior in the system of emitter-dressed Ag nanorods. Starting from the Drude model for the plasmon oscillations, we arrive at a semiempirical Hamiltonian describing the coupling between quantized surface plasmon modes and the quantum emitters that can be controlled by manipulating their geometry, spacing, and orientation. Further, identifying the lowest polariton mode as SP-states dressed by excitons in the vicinity of k = 0, we examine conditions allowing for the polariton quantum-phase transition. Though the system is formally a 1D array, we show that the polariton states of interest can undergo a quantum-phase transition to form a Bose condensate at finite temperatures for physically accessible parameter ranges.

Kibble-Zurek Mechanism in Topologically Nontrivial Zigzag Chains of Polariton Micropillars.

We consider a zigzag chain of coupled micropillar cavities, taking into account the polarization of polariton states. We show that the TE-TM splitting of photonic cavity modes yields topologically protected polariton edge states. During the strongly nonadiabatic process of polariton condensation, the Kibble-Zurek mechanism leads to a random choice of polarization, equivalent to the dimerization of polymer chains. We show that dark-bright solitons appear as domain walls between polarization domains, analogous to the Su-Schrieffer-Heeger solitons in polymers. The soliton density scales as a power law with respect to the quenching parameter.

Observation of Fano-Type Interference in a Coupled Cavity-Atom System**Supported by the National Basic Research Program of China under Grant No 2012CB922101, and the National Natural Science Foundation of China under Grant No 11404375. Yi-Fu Zhu was supported by the National Science Foundation of USA under Grant No 1205565.

We present the experimental observation of the Fano-type interference in a coupled cavity-atom system by confining the laser-cooled 85Rb atoms in an optical cavity. The asymmetric Fano profile is obtained through quantum interference in a three-level atomic system coherently coupled to a single mode cavity field. The observed Fano profile can be explained by the interference between the intra-cavity dark state and the polariton state of the coupled cavity-atom system. The possible applications of our observations include all-optical switching, optical sensing and narrow band optical filters.

Polaritons in a nonideal periodic array of microcavities

The virtual crystal approximation is employed to numerically model the propagation of localized electromagnetic excitations through a two-dimensional array of coupled microcavities containing atomic clusters (quantum dots). The constructed model allows for the presence of defects (absence of cavities and/or quantum dots) at certain sites of the supercrystal. We derive the dispersion relations for polaritonic modes as functions of defect concentrations. This permits to evaluate the densities of states of polaritons and their effective masses as well as the band gaps for any prescribed values of defect concentrations.

Strong light‐matter coupling between a molecular vibrational mode in a PMMA film and a low‐loss mid‐IR microcavity

Microcavity devices exhibiting strong light‐matter coupling in the mid‐infrared spectral range offer the potential to explore exciting open physical questions pertaining to energy transfer between heat and light and can lead to a new generation of efficient wavelength tunable mid‐infrared sources of coherent light based on polariton Bose‐Einstein Condensation. Vibrational transitions of organic molecules, which often have strong absorption peaks in the infrared and considerably narrower linewidths than organic excitonic resonances, can generate polaritonic states in the mid‐infrared spectral range using microcavity devices. Here, narrow linewidth polaritonic resonances are exhibited in the mid‐infrared by coupling the carbonyl stretch vibrational transition of a polymethyl methacrylate film to the photonic resonance of a low optical‐loss mid‐infrared microcavity, which consisted of two Ge/ZnS dielectric Bragg reflectors. Rabi‐splitting of 14.3 meV is observed, with a 4.4 meV polariton linewidth at anti‐crossing. The large Rabi‐splitting relative to linewidth indicates efficient impedance‐matching between the bare vibrational and photonic states, and suggests molecular‐vibration polaritons incorporated in dielectric microcavities can be an enabling step towards realizing polariton optical switching and polariton condensation in the mid‐infrared spectral range.

Effect of a noisy driving field on a bistable polariton system

We report on the effect of noise on the characteristics of the bistable polariton emission system. The present experiment provides a time-resolved access to the polariton emission intensity. We evidence the noise-induced transitions between the two stable states of the bistable polaritons. It is shown that the external noise specifications, intensity and correlation time, can efficiently modify the polariton Kramers time and residence time. We find that there is a threshold noise strength that provokes the collapse of the hysteresis loop. The experimental results are reproduced by numerical simulations using Gross-Pitaevskii equation driven by a stochastic excitation.

Transient optical parametric oscillations in resonantly pumped multistable cavity polariton condensates

Transitional processes accompanying switches between steady states in multistable cavity polariton systems are studied experimentally in a low-symmetry high-$Q$ microcavity under resonant optical excitation at normal incidence. We show that the establishment of a high-energy polariton state is influenced by an optical parametric oscillation. Therefore, the emission spectrum reveals the energy-separated signal-idler pairs in both spin components. Accordingly, the time dependencies of the polariton emission exhibit oscillations whose periods correspond to the spectral positions of the scattered states. Thus, the sharp transitions between the steady states of a no-equilibrium polariton condensate enable one to visualize the near-condensate eigenmodes and explore their spectral and spin properties depending on the condensate amplitude and average spin.