Tunable Magnetic Alignment between Trapped Exciton-Polariton Condensates

Abstract

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]

Stochastic spin flips in polariton condensates: nonlinear tuning from GHz to sub-Hz

“…In this context, our work paves the way for a polariton RNG that can be easily parallelised by creating multiple disconnected trapped condensates on the same chip. It would also be interesting to study how the spin-power phase diagram reported here may change in the case of Josephson-coupled pairs [17], and spin lattices of polariton condensates [18].…”

“…Optical trapping methods are particularly flexible since they allow on-the-fly tuning of the condensate [11][12][13], and using spatially-patterned non-resonant pumps has proven to be a particularly simple and robust method. Using this technique, it is possible to create and control trapped polariton condensates [14][15][16], as well as larger arrays of condensates in which to study phase transitions in lattices [17,18]. An unexpected result of this optical trapping is the observation of a parity-breaking symmetry bifurcation where the condensate spontaneously adopts a macroscopic spin and emits corresponding right-or left-circular polarisation [19], thanks to the reduced interactions with reservoir excitons.…”

Hybrid organic-inorganic polariton laser

“…The ease of creation and manipulation of polariton Bose-Einstein condensates 1–5 through direct optical pumping of semiconductor microcavities has recently led to demonstrations of numerous prototype polaritonic devices including low threshold lasers 6–9 , interferometers 10 and transistor devices 11 . The later are almost entirely based on GaAs semiconductors that offer superior material quality, despite the restriction to low temperature operation due to the small exciton binding energy in this material 12, 13 .…”

Spinor polariton condensates under nonresonant pumping: Steady states and elementary excitations

“…This has resulted in numerous intriguing phenomena even in one-component polariton condensates [6][7][8][9][10][11][12][13][14]. Further account of the polariton spin degree of freedom and their dynamics have revealed exceptionally rich physics in polariton systems [1], such as the stimulated spin dynamics of polaritons [15,16], spin Meissner effect [17][18][19][20], optical spin Hall effect [21][22][23][24], spontaneous spin bifurcation [25], and ferromagnetic-antiferromagnetic phase transitions [26,27] in spinor polariton Bose-Einstein condensate (BEC). Second, owing to the inherent spin multi-stabilities [28,29] and fast spin dynamics, semiconductor microcavities bring prospects of implementing novel solid-state optoelectronic spin-logic architectures [30].…”