Semiconductor microcavities are used to support freely flowing polariton quantum liquids allowing the direct observation and optical manipulation of macroscopic quantum states. Incoherent optical excitation at a point produces radially expanding condensate clouds within the planar geometry. By using arbitrary configurations of multiple pump spots, we discover a geometrically controlled phase transition, switching from the coherent phase-locking of multiple condensates to the formation of a single trapped condensate. The condensation threshold becomes strongly dependent on the programmed superfluid geometry and sensitive to cooperative interactions between condensates. We directly image persistently circulating superfluid and show how flows of light-matter quasiparticles are dominated by the quantum pressure in such configurable laser-written potential landscapes.

Tunneling of electrons through a potential barrier is fundamental to chemical reactions, electronic transport in semiconductors and superconductors, magnetism, and devices such as terahertz oscillators. Whereas tunneling is typically controlled by electric fields, a completely different approach is to bind electrons into bosonic quasiparticles with a photonic component. Quasiparticles made of such light-matter microcavity polaritons have recently been demonstrated to Bose-condense into superfluids, whereas spatially separated Coulomb-bound electrons and holes possess strong dipole interactions. We use tunneling polaritons to connect these two realms, producing bosonic quasiparticles with static dipole moments. Our resulting three-state system yields dark polaritons analogous to those in atomic systems or optical waveguides, thereby offering new possibilities for electromagnetically induced transparency, room-temperature condensation, and adiabatic photon-to-electron transfer.

Polariton condensates are macroscopic quantum states formed by half-matter half-light quasiparticles, thus connecting the phenomena of atomic Bose-Einstein condensation, superfluidity, and photon lasing. Here we report the spontaneous formation of such condensates in programmable potential landscapes generated by two concentric circles of light. The imposed geometry supports the emergence of annular states that extend up to 100 μm, yet are fully coherent and exhibit a spatial structure that remains stable for minutes at a time. These states exhibit a petal-like intensity distribution arising due to the interaction of two superfluids counterpropagating in the circular waveguide defined by the optical potential. In stark contrast to annular modes in conventional lasing systems, the resulting standing wave patterns exhibit only minimal overlap with the pump laser itself. We theoretically describe the system using a complex Ginzburg-Landau equation, which indicates why the condensate wants to rotate. Experimentally, we demonstrate the ability to precisely control the structure of the petal condensates both by carefully modifying the excitation geometry as well as perturbing the system on ultrafast timescales to reveal unexpected superfluid dynamics.interferometer | rings | BEC | SQUID C ircular loops are a key geometry for superfluid and superconducting devices because rotation around a closed ring is coupled to the phase of a quantum wavefunction; so far, however, they have not been optically accessible, although this would enable a new class of quantum devices, particularly if room temperature condensate operation is achieved.In lasing systems with an imposed circular symmetry, an annulus of lasing spots can sometimes form along the perimeter of the structure (1-6). Such transverse modes are often referred to as "petal states" (1) or "daisy modes" (2) and are interpreted as annular standing waves (3), whispering gallery modes (4), or coherent superpositions of Laguerre-Gauss (LG) modes with zero radial index (5, 6). Their circular symmetry makes them interesting for numerous applications such as free space communication or fiber coupling (7), and their LG-type structure suggests implementations using the orbital angular momentum of light (8), such as optical trapping (9) or quantum information processing (10). Petal states have been reported for various conventional lasing systems, including electrically and optically pumped vertical cavity surface-emitting lasers (VCSELs) (2, 4), as well as microchip (6) and rod lasers (1).A fundamentally different type of lasing system is the polariton laser (11,12). Polaritons are bosonic quasiparticles, resulting from the strong coupling between microcavity photons and semiconductor excitons (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21). Their small effective mass (bestowed by their photonic component) and strong interactions (arising from their excitonic component) favor Bose-stimulated condensation into a single quantum state, called a polariton condensate (14,15). These full...

Exciton polaritons in high quality semiconductor microcavities can travel long macroscopic distances (>100  μm) due to their ultralight effective mass. The polaritons are repelled from optically pumped exciton reservoirs where they are formed; however, their spatial dynamics is not as expected for pointlike particles. Instead we show polaritons emitted into waveguides travel orthogonally to the repulsive potential gradient and can only be explained if they are emitted as macroscopic delocalized quantum particles, even before they form Bose condensates.

Direct electrical detection of the dispersion of electrically tuned light-matter strong coupling and consequent mapping of the polariton dispersion is achieved by tunneling photocurrent out of reverse-biased p-in microcavity structures. The coherent photon-assisted tunneling is based on mixing cavity photons into the electronic states. Associated with this double-quantum-well tunneling we demonstrate the optical bistability of polaritons maintained within the strong-coupling regime. An intrinsic hole population gates bistability through the local modulation of the potential profile produced by an optically controlled buildup of free carriers within the quantum wells.

In this paper, we present a novel experimental scheme for the complete control of photoexcitation of microcavity polaritons. We show that this method can easily be adapted to generating either polarisation or frequency entangled photons.The experimental study of polariton-polariton scattering is demanding, because it requires simultaneous control of both the excitation energy and momentum. The standard approaches to the problem are using goniometers, slits, or tilting mirrors. Common in these methods is the presence of one or more moving optical elements, which, in turn, leads to experimental limitations, because it is difficult to keep the pointing of the excitation beams.Instead of applying any of the above-mentioned methods, we achieve the same goal without any moving parts, thereby, considerably simplifying the experiments, and removing one of the most serious disadvan tages.Our method makes use of spatial light modulators (SLM). The sample is excited through a high-NA microscope objective, which converts beam positions into angles. A phase-modulated SLM is used to shift the beams (momentum control), while an amplitude-modulated SLM cuts out pre-defined colours from the spectrum of the dispersed light of a fs laser (energy control). Light is collected through a microscope objective, and optical fibres. Momentum selection is done by changing the position of the collection fibres. FIG. 1: Experimental setup for two-colour excitation of micro cavity polaritons.In the paper, we will present our experimental method, and the first results related to polariton polariton scattering in planar GaAs micro cavities grown by molecular beam epitaxy (MBE). We will also discuss how our implementation can be used for creating either polarisation or frequency entangled photons, based on the schemes proposed in the theoretical papers of Porto Ian [2] (polarisation), and Ciuti [1] (frequency).

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