Coupled counterrotating polariton condensates in optically defined annular potentials

Abstract

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...

Sagnac interferometry with coherent vortex superposition states in exciton-polariton condensates

“…Once the characteristic interference of the OAM superposition (consisting of 2l lobes) has been transfered to the polariton BEC, the Sagnac phase can then be determined from the angular velocity of the BEC cloud. We can obtain an ordinary vortex state here simply by setting either α or β = 0 [46]. Many lasers emit light beams which approximate a Gaussian profile with l = p = 0.…”

“…For the BEC case the Sagnac phase for polaritons can be written [74] φ Ω (t) = N (t) 4mA loop h Ω. (22) where N (t) is the number of times a polariton revolves around the loop in a time t. In a ring geometry of radius r as seen in [46,75], we have for counter-propagating momenta ±k 0…”

Stability of persistent currents in open dissipative quantum fluids

“…The formal non-compliance with the traditional Landau criterion of superfluidity should not impede observation of persistent currents due to suppressed development of energetic instability in dissipative superfluids. The possibility to create a polariton condensate in an optically induced annular trap has already been explored experimentally, and spontaneous formation of vortices and patterns has been observed in such traps [20][21][22]. Provided that coherent imprinting of orbital angular momentum [30] can be realised for these systems, the test of our predictions could be feasible.…”

“…If the inward polariton flow does not decay fast enough, then polaritons might form a central density peak [25,26]. This phenomenon will not occur in non-zero angular momentum states [21], since the phase singularity is associated with a vanishing density at the vortex core [5].…”

Pattern formation in non-equilibrium spinor polariton condensates

“…In Fig 6 (a) and (b) the schematics of the four pump spot setting is provided. The results are based on the experimental finding that the condensate forms away from the areas where they are created by external illumination through laser beams that act as repulsive potentials [18]. This is possible as polaritons have a relative long lifetime compared to excitons.…”