Macroscopic Two-Dimensional Polariton Condensates

Abstract

We report a record-size polariton condensate of a fraction of a millimeter. This macroscopically occupied state of macrosopic size is not constrained to the excitation spot and is free from the usual complications brought by high-energy reservoir excitons, which strongly alter the physics of polaritons, including their mobility, energy distribution and particle interactions. The density of this trap-free condensate is lower than 1 polariton/µm 2 , reducing the phase noise induced by the interaction energy. Experimental findings are backed up by numerical simulations using a hydrodynamic model which takes into account both the polariton expansion and the phonon-assisted relaxation towards the lowest energy state. These results propel polariton condensates at the fundamental level set by their cold-atomic counterparts by getting rid of several solid-state difficulties, while still retaining their unique driven/dissipative features.PACS numbers: 71.36.+c, 63.20.Ls, 67.25.dg, 42.50.Ct Under suitable conditions, light-matter interaction can be strong enough to drive the coherent exchange of energy between photonic and electronic modes [1]. This is the paradigm of microcavity exciton-polaritons: quasiparticles created by the strong coupling between the photonic mode of a microcavity and the excitonic transition of semiconductor quantum wells [2]. Polaritons manifest their composite nature with a combination of photonic and excitonic properties [3]. Thanks to their photonic component, polaritons can ballistically propagate in the plane of the microcavity with velocities up to a few percent of the speed of light [4]. On the other hand, the exciton component results in strong optical nonlinearities and induces an energy renormalization of the polariton dispersion at high densities [5]. This energy shift can be much larger than the linewidth and is at the foundation of most polaritonic effects and applications [6][7][8]. As bosonic quasiparticles, polaritons experiment final-state stimulated scattering, which results, above a density threshold, in a laser-like emission without population inversion, a collective phenomenon that is explained in the framework of Bose-Einstein condensation [9][10][11]. A unique feature of polariton condensates is their driven/dissipative nature, in which the steady state is reached through a dynamical balance of pumping and dissipation.Polariton condensate have been experimentally observed in different materials, both inorganic [12][13][14][15] and organic semiconductors [16,17], and thanks to their light mass, condensation is achieved also at room temperature [18]. However, differently from their atomic counterpart, these condensates suffer from dephasing and density fluctuations induced by the interactions with the exciton reservoir, effectively resulting in multimode condensates [19][20][21]. The exciton reservoir also acts as a trapping mechanism, if the polariton lifetime is too short, confining the condensation process within the region of the excitation spot [22][23][24][25]. Moreov...

Polariton-enhanced exciton transport

“…A similar population on the opposite side and with opposite momentum is also visible in Figure 2 The momentum of this backscattered population increases with increasing distance away from the pump spot. We do not fully understand this process, but we note that backscattered populations have been reported in similar samples under similar experimental conditions 36 . This phenomenon could possibly be explained by the self interference of a population of polaritons with the positive and negative effective diffusive masses corresponding to momenta below and above the lower inflection point, respectively 37 .…”

Quantum computing with exciton-polariton condensates

“…36 Finally, it is notable that typical polariton micropillar lattices can be fabricated with micron scale precision, 3 while the coherence of polariton condensates has been reported extending over a fraction of a millimeter. 37 The state-of-the-art in quantum computing has been developing rapidly in recent years, with companies developing systems with around 50 qubits, 38 while superconducting qubit systems 39 and ion trap 40 systems have already achieved 8 and 20 qubits, respectively. We hope that polariton lattices, which can potentially have a size of around 100 × 100 = 10 4 qubits (or double accounting for spin), will also be seen as relevant candidates.…”

Magnon condensation in a dense nitrogen-vacancy spin ensemble

“…Magnons, or spin-wave quanta, constitute propagating disturbances in a correlated array of magnetic spins [12,13], and whose modes and dynamics are being intensely studied in a variety of systems in the pursuit of both fundamental many-body states [14], and practical information technology [15,16]. While the manifestation of spin-waves in magnetic media is ubiquitous, their room-temperature quantum condensation is a recently observed phenomenon, and presents a compelling platform for exploring many-body and macroscopic quantum dynamics at room temperature [4,[17][18][19]. Given the central role of spin-lattice relaxation, it is compelling to consider their manifestation and condensation in magnetically doped crystals with long-lived spin systems, and for which additional degrees of spin manipulation may be available.…”