Polariton Condensates

Most real-world optimization problems become very hard to solve for traditional classical computers due to the exponential growth in the number of operations with an increasing number of variables. These optimization challenges can be efficiently mapped onto Classical spin Hamiltonians, including Ising, Clock, XY,  etc. The need for advanced technology and the constraints of classical computing have stimulated the creation of new innovative approaches including analog simulators based on the systems of coupled exciton-polariton condensates that at their equilibrium, can provide solutions to optimization tasks.

Exciton–polaritons are superpositions of an excitons and a photons that can emerge in the reflective microcavities as a result of the strong coupling between quanta of light (photons) induced by the laser beam and elementary excitations (excitons) in semiconductor microcavities. Excitonic component of formed condensate is strongly sensitive to cavity heterostructure, external fields and other excitons and polaritons. This sensitivity allows for the manipulation of exciton-polaritons by light, enabling the fine-tuning of their characteristics, and facilitating their organization into highly controllable arrays of collective coherent modes (condensates) coupled to each other via tunable spatial overlapping. These arrays can be alternatively generated using spatially modulating non-resonant laser that serves not only as a local gain for polaritons but also creates a local trapping potential by exciting hot excitons, which repel polaritons and act as potential barriers.

These arrays show significant potential in creating ultrafast simulators capable of modeling spin ordering, synchronization in lattices, neural networks and optimization problem solvers. These advantages stem from the capability of polariton condensates to establish phase-locked final states within a picoseconds and sustain them long enough at room temperatures to carry out the measurement of "spins" encoded by phases of spatially arranged condensates. While simulated annealing techniques slide to the ground state from above and may become trapped in local minima, systems of our interest take a different mechanism. They approach the minimum from below by slowly increasing gain that pushes the system to a coherent state with highest total number of condensed particles and, therefore, minimizes the spin-Hamiltonian.

Polariton simulators offer distinct advantages, being free from scaling difficulties, amenable to fabrication within compact form-factor systems, capable of operation at room temperatures, and achievable within relatively short timescales using diverse experimental platforms with tunable properties. Furthermore, the recent attainment of the onset of quantum regime by exciton–polaritons adds to their promise. Exploring the influence of quantum corrections on the efficiency of analog simulators utilizing exciton-polariton condensate platforms holds particular intrigue in this context.