Elementary quasi-particles in a two dimensional electron system can be described as exciton-polarons since electron-exciton interactions ensures dressing of excitons by Fermi-sea electron-hole pair excitations. A relevant open question is the modification of this description when the electrons occupy flat-bands and electron-electron interactions become prominent. Here, we perform cavity spectroscopy of a two dimensional electron system in the strong-coupling regime where polariton resonances carry signatures of strongly correlated quantum Hall phases. By measuring the evolution of the polariton splitting under an external magnetic field, we demonstrate the modification of electron-exciton interactions that we associate with phase space filling at integer filling factors and polaron dressing at fractional filling factors. The observed non-linear behavior shows great promise for enhancing polariton-polariton interactions. PACS numbers: 71.36.+c, 73.43.Fj Strong coupling of excitons in a semiconductor quantum well (QW) to a microcavity mode leads to formation of quasiparticles called cavity exciton polaritons [1]. Polaritons have played a central role in the investigation of nonequilibrium condensation and superfluidity of photonic excitations [2,3]. While polaritons acquire a finite nonlinearity due to their exciton character, interactions between polaritons in undoped QWs are not strong enough for realizing strongly interacting photonic systems [4]. Two-dimensional electron systems (2DES) evolving in large magnetic fields, in contrast, are a fertile ground for many-body physics due to prominence of electron-electron interactions. Formation of skyrmion excitations in the vicinity of filling factor ν = 1 is a consequence of such interactions. More spectacularly, electron correlations lead to the formation of fractional quantum Hall (FQH) states where the ground state exhibits topological order [5][6][7]. Moreover, it has been proposed that a sub-class of FQH states exhibit nonabelian quasi-particles which can be used to implement topological quantum computation [8]. The nature of optical excitations of a 2DES have also recently generated lots of interest: experimental and theoretical [9, 10] studies in transition metal dichalcogenide (TMD) monolayers have established that these excitations should be described in the framework of the Fermi polaron problem, as a collective excitation resulting from exciton-electron interactions [11][12][13][14]. In this context, optical excitation of an exciton leads to generation of an electron screening cloud that results in formation of a lower energy attractive exciton-polaron [9,10]. In this work, we report corresponding signatures in GaAs, where energy scales are known to differ significantly compared to TMD monolayers [15,16], due to a particularly small binding energy of the bound-molecular trion state. More importantly, our work presents experimental signatures of polaron formation at nonzero magnetic fields where electrons are confined to the lowest Landau level.It has r...

We report polarization-resolved resonant reflection spectroscopy of a charge-tunable atomically-thin valley semiconductor hosting tightly bound excitons coupled to a dilute system of fully spin-and valley-polarized holes in the presence of a strong magnetic field. We find that exciton-hole interactions manifest themselves in hole-density dependent, Shubnikov-de Haas-like oscillations in the energy and line broadening of the excitonic resonances. These oscillations are evidenced to be precisely correlated with the occupation of Landau levels, thus demonstrating that strong interactions between the excitons and Landau-quantized itinerant carriers enable optical investigation of quantum-Hall physics in transition metal dichalcogenides. arXiv:1812.08772v1 [cond-mat.mes-hall]

These authors contributed equally to this work.Engineering strong interactions between optical photons is a great challenge for quantum science. Envisioned applications range from the realization of photonic gates for quantum information processing [1] to synthesis of photonic quantum materials for investigation of strongly-correlated drivendissipative systems [2]. Polaritonics, based on the strong coupling of photons to atomic or electronic excitations in an optical resonator, has emerged as a promising approach to implement those tasks [3]. Recent experiments demonstrated the onset of quantum correlations in the exciton-polariton system [4,5], showing that strong polariton blockade [6] could be achieved if interactions were an order of magnitude stronger. Here, we report time resolved four-wave mixing experiments on a two-dimensional electron system embedded in an optical cavity [7], demonstrating that polariton-polariton interactions are strongly enhanced when the electrons are initially in a fractional quantum Hall state. Our experiments indicate that in addition to strong correlations in the electronic ground state, exciton-electron interactions leading to the formation of polaron polaritons [8-11] play a key role in enhancing the nonlinear optical response. Besides potential applications in realization of strongly interacting photonic systems, our findings suggest that nonlinear optical measurements could provide information about fractional quantum Hall states that is not accessible in linear optical response.Polaritons have recently attracted considerable interest, motivated by the fact that their interactions can be engineered almost at will through the tunability of their matter component. For example, strongly interacting Rydberg polaritons have recently been obtained using the nonlinear behavior of Rydberg excitations in an ensemble of atoms [12], which led to the demonstration of Rydberg polariton blockade [13] where the presence of a single polariton in a well-delimited region of space prevents the resonant injection of other polaritons. In parallel, efforts are being made to realize polariton blockade in condensed matter systems that hold great potential for realizing compact and integrated synthetic quantum materials [3]. Exciton polaritons in semiconductor materials are part light part matter particles that arise from the strong coupling of a quantum well exciton and a cavity photon [14]. These photonic particles inherit a nonlinear behavior from exciton-exciton interactions [2,15,16]. For efficient blockade to be obtained, the nonlinearity U needs to be greater than the inverse lifetime γ of the polaritons [6]. Recent state-of-the art experiments based on photon correlation measurements in semi-integrated microcavities attained optimized values of the ratio U/γ 0.1 in a photonic dot with about 3 µm 2 area [4,5]. These experiments represent the culmination of decade long technological developments aimed at increasing U/γ through reducing the photonic mode area [17][18][19] as well as increasing t...

It is widely assumed that photons cannot be manipulated using electric or magnetic fields. Even though hybridization of photons with electronic polarization to form exciton-polaritons has paved the way to a number of ground-breaking experiments in semiconductor microcavities, the neutral bosonic nature of these quasiparticles has severely limited their response to external gauge fields. Here, we demonstrate polariton acceleration by external electric and magnetic fields in the presence of nonperturbative coupling between polaritons and itinerant electrons, leading to formation of new quasiparticles termed polaron-polaritons. We identify the generation of electron density gradients by the applied fields to be primarily responsible for inducing a gradient in polariton energy, which in turn leads to acceleration along a direction determined by the applied fields. Remarkably, we also observe that different polarization components of the polaritons can be accelerated in opposite directions when the electrons are in ν = 1 integer quantum Hall state.Controlling photons with external electric or magnetic fields is an outstanding goal. On the one hand, coupling photons to artificial gauge fields holds promises for the realization of topological and strongly correlated phases of light [1][2][3][4]. On the other hand, effecting forces on photons constitutes both a problem of fundamental interest in electromagnetism and an important step in view of technological applications [5][6][7][8]. One promising avenue towards this goal is to hybridize photons with material excitations that are genuinely sensitive to gauge fields [9]. In this non-perturbative regime, exciton-polariton states are formed, ensuring that the forces acting on the material excitations are directly imprinted onto the photon. However, the neutral bosonic nature of polaritons has so far severely limited their response to gauge fields [10][11][12][13].A particularly appealing approach to circumvent this limitation is to leverage on the interaction between excitons and charges. Indeed, early reports on the drift of trions in an electric field [14,15], as well as on the Coulomb drag effect in bilayer systems [16][17][18][19] indicated that it may be possible to manipulate neutral excitations using electric fields in a solid-state setting. Recently, experimental [20] and theoretical studies [21] reported the electrical control of the speed of a polariton superfluid, raising new questions and possibilities regarding the interplay between the normal and condensed fractions of the fluid in the presence of electron-exciton interactions.While interactions between polaritons and electrons have been proposed and analyzed as a mechanism for polariton thermalization [22][23][24][25], early studies reported the modifications to polariton resonances in the presence of a Fermi sea [26][27][28]. These modifications stem form dispersive interactions between the polarizable excitonic component of the polariton with the charge-density fluctuations of the Fermi sea [29][30][31]. ...

We show that optically active coupled quantum dots embedded in a superconducting microwave cavity can be used to realize a fast quantum interface between photonic and transmon qubits. Single photon absorption by a coupled quantum dot results in generation of a large electric dipole, which in turn ensures efficient coupling to the microwave cavity. Using cavity parameters achieved in prior experiments, we estimate that bi-directional microwave-optics conversion in nanosecond timescales with efficiencies approaching unity is experimentally feasible with current technology. We also outline a protocol for in-principle deterministic quantum state transfer from a time-bin photonic qubit to a transmon qubit. Recent advances in quantum dot based quantum photonics technologies indicate that the scheme we propose could play a central role in connecting quantum nodes incorporating cavity-coupled superconducting qubits.Introduction. A quantum interface between flying photonic and stationary matter qubits is widely regarded as an essential element of quantum networks [1][2][3]. Remarkable advances over the last decade have established that circuit-QED, consisting of superconducting (SC) qubits non-perturbatively coupled to a common microwave (MW) cavity, is particularly promising for realization of small-scale quantum information processors [4,5]. The most prominent limitation in realization of quantum networks consisting of circuit-QED based processors is the difficulty in transferring quantum information over distances exceeding meters. Motivated by overcoming this roadblock, several groups have embarked on research aimed at creating a quantum interface between SC qubits and propagating photonic qubits. Among the several ingenuous proposals [6][7][8][9][10][11][12][13][14][15] to resolve this conundrum, the approach based on using optomechanical coupling [16][17][18][19][20] has proven to be particularly successful: pioneering experiments have demonstrated conversion efficiency of 10% with a bandwidth of 30 kHz [20]. A limitation for most if not all of these approaches is the relatively small effective coupling strength between the single optical and MW photons, which in turn prevents conversion of quantum information on time-scales much shorter than typical SC qubit coherence times.

When Landau levels (LLs) become degenerate near the Fermi energy in the quantum Hall regime, interaction effects can drastically modify the electronic ground state. We study the quantum Hall ferromagnet formed in a two-dimensional hole gas around the LL filling factor ν ¼ 1 in the vicinity of a LL crossing in the heave-hole valence band. Cavity spectroscopy in the strong-coupling regime allows us to optically extract the spin polarization of the two-dimensional hole gas. By analyzing this polarization as a function of hole density and magnetic field, we observe a spin flip of the ferromagnet. Furthermore, the depolarization away from ν ¼ 1 accelerates close to the LL crossing. This is indicative of an increase in the size of skyrmion excitations as the effective Zeeman energy vanishes at the LL crossing.

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