A polariton condensate transistor switch is realized through optical excitation of a microcavity ridge with two beams. The ballistically ejected polaritons from a condensate formed at the source are gated using the 20 times weaker second beam to switch on and off the flux of polaritons. In the absence of the gate beam the small builtin detuning creates potential landscape in which ejected polaritons are channelled toward the end of the ridge where they condense. The low loss photon-like propagation combined with strong nonlinearities associated with their excitonic component makes polariton based transistors particularly attractive for the implementation of all-optical integrated circuits. 71.36.+c Contemporary electronics face ever increasing obstacles in achieving higher speeds of operation. Down-scaling which has served Moore's law for decades is approaching the inherent limits of semiconductor materials [1][2][3][4]. Even though a number of novel approaches [5][6][7] have managed to improve operating frequency and power consumption, it is commonly acknowledged that in the future, charged carriers will have to be replaced by information carriers that do not suffer from scattering, capacitance and resistivity effects. Although photonic circuits have been proposed, a viable optical analogue to an electronic transistor has yet to be identified as switching and operating powers of these devices are typically high [8].Polaritons which are hybrid states of light and electronic excitations offer an attractive solution as they are a natural bridge between these two systems. Their excitonic component allows them to interact strongly giving rise to the nonlinear functionality enjoyed by electrons. On the other hand, their photonic component restricts their dephasing allowing them to carry information with minimal data loss. Notably from the view of solid state physics polaritons are bosonic particles with a particularly light effective mass. These properties allow for the condensation of polaritons into a massively occupied single low-energy state, which shows many similarities to atomic Bose Einstein condensates [9][10][11][12]. The macroscopic quantum properties of polariton condensates combined with their photonic nature make them ideal candidates for use in quantum information devices and all optical circuits [13][14][15][16][17]. Several recent works address the possibility of optical manipulation of polariton condensate flow however these stop short of demonstrating actual gating of polariton condensate flow a prerequisite for implementation of integrated optical circuits [17][18][19][20].In this paper, a high finesse microcavity sample fabricated into a ridge is utilized to develop an exciton-polariton condensate transistor switch. A polariton condensate formed by optical excitation serves as a source of polaritons which are ballis-tically ejected along the channel as shown in Figure 1(a). Polariton propagation can be controlled using a second weaker beam that gates the polariton flux by modifying the energy ...

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.

Tunable spin correlations are found to arise between two neighboring trapped exciton-polariton condensates which spin-polarize spontaneously. We observe a crossover from an antiferromagneticto a ferromagnetic pair state by reducing the coupling barrier in real-time using control of the imprinted pattern of pump light. Fast optical switching of both condensates is then achieved by resonantly but weakly triggering only a single condensate. These effects can be explained as the competition between spin bifurcations and spin-preserving Josephson coupling between the two condensates, and open the way to polariton Bose-Hubbard ladders.The development of spin-charge lattice models for understanding strongly-correlated states of matter is a successful theme of modern quantum physics. This has driven the desire to model and probe complex condensed matter phenomena using highly-controlled systems, such as ultracold atoms [1], photons [2,3], or superconducting junctions [4]. Exciton-polariton (polariton) lattices have emerged as an alternative system [5, 6] with unique properties. Due to their strongly dissipative and nonlinear nature, many-body polariton gases can reach steady states which are remarkably different from their equilibrium case [7]. Moreover, they have peculiar spin properties [8][9][10] and exhibit spontaneous magnetization (emitting circularly polarized light) above a critical bifurcation threshold [11], analogous to the weak lasing regime [12]. In this Letter we study the basic building block of a polariton spin lattice: two optically trapped spin-polarized condensates which are tunably coupled. We demonstrate that trapped out-of-equilibrium polariton condensates can exhibit Ising-like behavior related to spin bifurcations. The two condensate system investigated here is shown to correspond to one plaquette of a bosonic ladder [13], and allows demonstration of a crossover in the competition between Josephson coupling and spin bifurcation. These features have not been seen in any other system to date.Polariton condensates are coherent many-body states [14][15][16][17], which can be confined in potentials [18][19][20] and interact with each other via Josephson junctions [21][22][23][24]. For a pair of interacting trapped spin-polarized condensates, their polarization states are expected to couple. However, the driven-dissipative and nonlinear nature of polariton condensates makes * ho278@cam.ac.uk † jjb12@cam.ac.uk the underlying coupling mechanism considerably richer than that in the conventional Ising case, leading to exotic forms of magnetism where the orientation and strength of coupling is not determined by the sign of the interaction.We achieve tuning between ferromagnetic (F) or antiferromagnetic (AF) coupling by directly modulating the tunneling barrier, adjusting either the height of the barrier or the separation between the condensates. We show arXiv:1603.02830v1 [cond-mat.other]