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Exciton polaritons in high quality semiconductor microcavities can travel long macroscopic distances ($g100\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$) 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.

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.

Direct electrical detection of the dispersion of electrically tuned light-matter strong coupling and consequent mappingofthepolaritondispersionisachievedbytunnelingphotocurrentoutofreverse-biased p-i-nmicrocavity structures.Thecoherentphoton-assistedtunnelingisbasedonmixingcavityphotonsintotheelectronicstates.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.

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 Through with a Light Touch Quantum tunneling underpins a host of essential techniques, such as scanning tunneling microscopy and quantum cascade lasers, as well as chemical reactions. The tunneling particles are normally electrons, and control of the tunneling process has generally been by electric fields. By coupling tunneling electrons with cavity photons trapped inside a semiconductor microcavity, Cristofolini et al. (p. 704 , published online 5 April; see the Perspective by Szymańska ) produced mixed states that then allowed direct optical control of the tunneling process. Such an optical-based approach to manipulating and controlling the tunneling process may find applications in quantum information science.