Coupling of quantum emitters in a semiconductor relies, generally, on short-range dipole-dipole or electronic exchange type interactions. Consistently, energy transfer between exciton states, that is, electron-hole pairs bound by Coulomb interaction, is limited to distances of the order of 10~nm. Here, we demonstrate polariton-mediated coupling and energy transfer between excitonic states over a distance exceeding 2~$μ$m. We accomplish this by coupling quantum well-confined excitons through the delocalized mode of two coupled optical microcavities. Use of magnetically doped quantum wells enables us to tune the confined exciton energy by the magnetic field and in this way to control the spatial direction of the transfer. Such controlled, long-distance interaction between coherently coupled quantum emitters opens possibilities of a scalable implementation of quantum networks and quantum simulators based on solid-state, multi-cavity systems.
Dark excitons are of fundamental importance for a wide variety of processes in semiconductors, but are difficult to investigate using optical techniques due to their weak interaction with light fields. We reveal and characterize dark excitons injected by non-resonant pulsed excitation in a semiconductor microcavity structure containing InGaAs/GaAs quantum wells by monitoring their interactions with the bright lower polariton mode. We find a surprisingly long dark exciton lifetime of more than 20 ns which is longer than the time delay between two consecutive pulses. This creates a memory effect…
We have experimentally observed an eddy current of exciton polaritons arising in a cylindrical GaAs/AlGaAs pillar microcavity under the nonresonant optical pumping. The polariton current manifests itself in a Mach-Zehnder interferometry image as a characteristic spiral that occurs due to the interference of the light emitted by an exciton-polariton condensate with a spherical wave artificially shaped from the emission of the same condensate. We have experimentally observed the condensates with the topological charges m = +1, m = -1 and m = -2. The interference pattern corresponding to the m = …
Planar Bragg microcavities with monolayer WS$_2$ for strong exciton-photon coupling
School of Physics and Engineering, ITMO University（ITMO大学物理与工程学院）；Department of Physics and Astronomy, University of Sheffield（谢菲尔德大学物理与天文学系）；Experimentelle Physik 2, Technische Universität Dortmund（多特蒙德工业大学实验物理第二系）
Exciton-polaritons in semiconductor microcavities generate fascinating effects such as long-range spatial coherence and Bose-Einstein Condensation (BEC), which are attractive for their potential use in low threshold lasers, vortices and slowing light, etc. However, currently most of exciton-polariton effects either occur at cryogenic temperature or rely on expensive cavity fabrication procedures. Further exploring new semiconductor microcavities with stronger exciton photon interaction strength is extensively needed. Herein, we demonstrate room temperature photon exciton strong coupling in hyb…
We demonstrate strong light-matter interaction at ambient conditions between a ladder-type conjugated polymer and the individual modes of a vertical microcavity with tunable resonance frequencies. Zero-dimensional wavelength-scale confinement for the polaritons is achieved through a sub-micron sized Gaussian defect, resulting in a vacuum Rabi splitting of the polariton branches of 2g = 166 meV. By placing a second Gaussian defect nearby, we create a polaritonic molecule with tunnel coupling strength of up to 2J ~ 50 meV. This platform enables the creation of tailor-made potential landscapes wi…
Exciton-polaritons are quasiparticles with mixed photon and exciton character that demonstrate rich quantum phenomena, novel optoelectronic devices and the potential to modify chemical properties of materials. Organic semiconductors are of current interest for their room-temperature polariton formation. However, within organic optoelectronic devices, it is often the 'dark' spin-1 triplet excitons that dominate operation. These triplets have been largely ignored in treatments of polariton physics. Here we demonstrate polariton population from the triplet manifold via triplet-triplet annihilatio…
Analysis of exciton-polariton condensation under different pumping schemes for 1D and 2D microcavities including the effect of strong correlation between polaritons
We consider exciton-photon coupling in semiconductor microcavities in which separate periodic potentials have been embedded for excitons and photons. We show theoretically that this system supports degenerate ground-states appearing at non-zero in-plane momenta, corresponding to multiple valleys in reciprocal space, which are further separated in polarization corresponding to a polarization-valley coupling in the system. Aside forming a basis for valleytronics, the multivalley dispersion is predicted to allow for spontaneous momentum symmetry breaking and two-mode squeezing under non-resonant …
We demonstrate control over light-matter coupling at room temperature combining a field effect transistor (FET) with a tuneable optical microcavity. Our microcavity FET comprises a monolayer tungsten disulfide WS$_2$ semiconductor which was transferred onto a hexagonal boron nitride flake that acts as a dielectric spacer in the microcavity, and as an electric insulator in the FET. In our tuneable system, strong coupling between excitons in the monolayer WS$_2$ and cavity photons can be tuned by controlling the cavity length, which we achieved with excellent stability, allowing us to choose fro…
We investigate the microscopic description of exciton-polaritons that involves electrons, holes and photons within a two-dimensional microcavity. We show that in order to recover the simplified exciton-photon model that is typically used to describe polaritons, one must correctly define the exciton-photon detuning and exciton-photon (Rabi) coupling in terms of the bare microscopic parameters. For the case of unscreened Coulomb interactions, we find that the exciton-photon detuning is strongly shifted from its bare value in a manner akin to renormalization in quantum electrodynamics. Within the…
The coupling between a 2D semiconductor quantum well and an optical cavity gives rise to combined light-matter excitations, the exciton-polaritons. These were usually measured when the conduction band is empty, making the single polariton physics a simple single-body problem. The situation is dramatically different in the presence of a finite conduction band population, where the creation or annihilation of a single exciton involves a many-body shakeup of the Fermi sea. Recent experiments in this regime revealed a strong modification of the exciton-polariton spectrum. Previous theoretical stud…
Here we report the fabrication and optical characterization of organic microcavities containing liquid-crystalline conjugated polymers (LCCPs): poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT), poly(9,9-dioctylfluorene) (PFO) and poly(2,7-(9,9-dihexylfluorene)-co-bithiophene) (F6T2) aligned on top of a thin transparent Sulfuric Dye 1 (SD1) photoalignment layer. We extract the optical constants of the aligned films using variable angle spectroscopic ellipsometry and fabricate metallic microcavities in which the ultrastrong coupling regime is manifest both for the aligned and non-aligned LCC…
We study experimentally the oscillations of a non stationary transient signal of a semiconductor microcavity with embedded InGaAs quantum wells. The oscillations occur as a result of quantum beats between the upper and lower polariton modes due to the strong exciton-photon coupling in the microcavity sample (Rabi oscillations). The registration of spectrally resolved signal has allowed for separate observation of oscillations at the eigenfrequencies of two polariton modes. Surprisingly, the observed oscillations measured at the lower and upper polariton modes have opposite phases. We demonstra…
Coherent control and manipulation of quantum degrees of freedom such as spins forms the basis of emerging quantum technologies. In this context, the robust valley degree of freedom and the associated valley pseudospin found in two-dimensional transition metal dichalcogenides is a highly attractive platform. Valley polarization and coherent superposition of valley states have been observed in these systems even up to room temperature. Control of valley coherence is an important building block for the implementation of valley qubit. Large magnetic fields or high-power lasers have been used in th…
We investigate the interactions between exciton-polaritons in N two-dimensional semiconductor layers embedded in a planar microcavity. In the limit of low-energy scattering, where we can ignore the composite nature of the excitons, we obtain exact analytical expressions for the spin-triplet and spin-singlet interaction strengths, which go beyond the Born approximation employed in previous calculations. Crucially, we find that the strong light-matter coupling enhances the strength of polariton-polariton interactions compared to that of the exciton-exciton interactions, due to the Rabi coupling …
Recent experiments in exciton-polariton systems have provided high-precision measurements of the value of the polariton-polariton interaction constant, which is a key parameter that governs the nonlinear dynamics of polariton condensates and potentially enables quantum correlated polaritons. Yet, until now, this parameter has only been addressed theoretically using perturbative treatments or approximations that do not include the composite nature of the excitons. Here, we use a recently developed microscopic description of polaritons involving electrons, holes, and photons, where the interacti…
Planar microcavities filled with active materials containing excitonic resonances host radiative exciton-polariton (polariton) modes with in-plane wave vectors within the light cone. They also host at least one mode guided in the cavity plane by total internal reflection and which is not radiatively coupled to the vacuum modes except through defects or sample edges. We show that polariton lasing mediated by polariton stimulated scattering can occur concomitantly in both types of modes in a microcavity. By adjusting the detuning between the exciton and the radiative photon mode one can favor po…
The interaction between coherent polaritons and incoherent excitons plays an important role in polariton physics. Using resonant pump-probe spectroscopy with selective excitation of single polariton branches, we investigate the different dephasing mechanisms responsible for generating a long-lived exciton reservoir. As expected, pumping the upper polariton results in a strong dephasing process that leads to the generation of a long lived reservoir. Unexpectedly, we observe an efficient reservoir creation while exciting only the lower polariton branch when the detuning is increased towards posi…
We study theoretically the photon statistics of the field emitted from two optically coupled semiconductor microcavities each containing a quantum well. The emission is determined by the interplay between exciton-photon coupling in each quantum well and internal interaction between the two optically coupled microcavities. A high degree of coherent control and tunability via the quantum well-cavity coupling strength and photon tunneling over the photon statistics of the transmitted field can be achieved. We demonstrate that the optical property of radiation emitted by one quantum well can be co…
Exciton polaritons in semiconductor microcavities exhibit many fundamental physical effects, with some of them amenable to being controlled by external fields. The polariton transport is affected by the polaritonic spin-orbit interaction, which is caused by the splitting of transverse-electric and transverse-magnetic (TE-TM) modes. This is the basis for a polaritonic Hall effect, called optical spin Hall effect (OSHE), which is related to the formation of spin/polarization textures in momentum space, determining anisotropic ballistic transport, as well as related textures in real space. Owing …
Collective (elementary) excitations of quantum bosonic condensates, including condensates of exciton polaritons in semiconductor microcavities, are a sensitive probe of interparticle interactions. In anisotropic microcavities with momentum-dependent TE-TM splitting of the optical modes, the excitations dispersions are predicted to be strongly anisotropic, which is a consequence of the synthetic magnetic gauge field of the cavity, as well as the interplay between different interaction strengths for polaritons in the singlet and triplet spin configurations. Here, by directly measuring the disper…
We investigate the many-body states of exciton-polaritons that can be observed by pump-probe spectroscopy. Here, a weak-probe `spin-down' polariton is introduced into a coherent state of `spin-up' polaritons created by a strong pump. We show that the $\downarrow$ impurities become dressed by excitations of the $\uparrow$ medium, and form new polaronic quasiparticles that feature two-point and three-point many-body quantum correlations, which, in the low density regime, arise from coupling to the vacuum biexciton and triexciton states respectively. In particular, we find that these correlations…
We develop a microscopic description of an electron-doped two-dimensional semiconductor embedded in a microcavity. Specifically, we investigate the interactions between exciton-polaritons and electrons for the case where the interactions between charges are strongly screened and the system is spin polarized. As a starting point, we obtain an analytic expression for the exciton-polariton wave function, and we relate the microscopic parameters of the light-matter system to experimentally measurable quantities, such as the Rabi coupling and the cavity photon frequency. We then derive the polarito…
We demonstrate the potential of quantum operation using lattices of exciton-polaritons in patterned semiconductor microcavities. By introducing an inverse four-wave mixing scheme acting on localized modes, we show that it is possible to develop non-classical correlations between individual condensates. This allows a concept of quantum exciton-polariton networks, characterized by the appearance of multimode entanglement even in the presence of realistic levels of dissipation.
