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  • Review Article
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Polariton condensates for classical and quantum computing

Nature Reviews Physics volume 4, pages 435–451 (2022)Cite this article

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A Publisher Correction to this article was published on 23 May 2022

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Abstract

Polariton lasers emit coherent monochromatic light through a spontaneous emission process. As a rare example of a system in which Bose–Einstein condensation and superfluidity are reported at room temperature, polariton lasers are interesting for fundamental research and offer potential for applications in classical and quantum information technologies. In the past 10 years, new material systems have emerged for polariton lasers, such as organic molecules, transition metal dichalcogenides, perovskites and liquid-crystal microcavities. In this Review, we discuss these emerging platforms in the context of applications in topological lasing, classical neuromorphic computing and quantum information processing.

Key points

  • Polariton lasers are coherent light emitters based on bosonic condensates of half-light, half-matter quasiparticles: exciton–polaritons.

  • Nowadays, polariton lasers with either optical or electronic injection are realized in a wide variety of organic, hybrid and inorganic systems, including two-dimensional crystals.

  • Engineering of spin–orbit coupling in polariton condensates led to the development of polariton topological insulators and lasers.

  • Phase locking in arrays of polariton condensates in planar microcavities may be used for the realization of ultrafast simulators.

  • Multistability of quasiresonantly pumped polariton condensates allows for realization of polariton neurons that pass information by means of the motion of domain walls.

  • Polariton qubits based on superposition of polariton superfluids with different orbital momenta are promising because of their high scalability and optical control.

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Fig. 1: Polariton laser structures.
Fig. 2: Topological polaritonics.
Fig. 3: Polaritonic neuromorphic computing.
Fig. 4: Polariton qubit based on a split-ring condensate.

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Acknowledgements

A.K. acknowledges the Rosatom Road Map for Quantum Computing programme. T.C.H.L. was supported by the Ministry of Education (Singapore) Tier 2 project MOE2019-T2-1-004. C.S. acknowledges funding provided by the European Research Council (ERC project 679288, unlimit-2D) as well as the German Research Foundation (DFG) (Project SCHN1376 14.1). S.K. and S.H. acknowledge financial support from the German Research Foundation (DFG) through the Würzburg–Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter “ct.qmat” (EXC 2147, project ID 390858490). S.K. acknowledges funding provided by the German Research Foundation (DFG) (Project KL3124/3.1).

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Authors and Affiliations

  1. Key Laboratory for Quantum Materials of Zhejiang Province, School of Science, Westlake University, Hangzhou, China

    Alexey Kavokin

  2. Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore

    Timothy C. H. Liew

  3. Institute of Physics, University of Oldenburg, Oldenburg, Germany

    Christian Schneider

  4. Skolkovo Institute of Science and Technology, Moscow, Russia

    Pavlos G. Lagoudakis

  5. Department of Physics and Astronomy, University of Southampton, Southampton, UK

    Pavlos G. Lagoudakis

  6. Technische Physik and Wilhelm-Conrad-Röntgen-Research Center for Complex Material Systems, University of Würzburg, Würzburg, Germany

    Sebastian Klembt & Sven Hoefling

  7. Würzburg–Dresden Cluster of Excellence ct.qmat, University of Würzburg, Würzburg, Germany

    Sebastian Klembt & Sven Hoefling

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  1. Alexey Kavokin
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  2. Timothy C. H. Liew
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  3. Christian Schneider
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  4. Pavlos G. Lagoudakis
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Glossary

Bragg mirror

A periodic dielectric structure that reflects light owing to the optical interference effect. Dielectric Bragg mirrors may provide higher reflectivities than metallic mirrors, which is why they are widely used in laser structures and microcavities.

Microcavity

A thin layer of semiconductor or dielectric material sandwiched between two mirrors. In contrast to conventional optical cavities, microcavities confine a limited number of optical modes, frequently only one mode, which is why they are characterized by a very high finesse.

Tamm-plasmon

An optical mode confined between a dielectric Bragg mirror and a metallic layer.

Frenkel exciton

An elementary excitation in a molecular crystal. Frenkel excitons are characterized by relatively small Bohr radii (of the order of a lattice constant) and large binding energies (typically of the order of 1 eV).

Wannier–Mott exciton

An elementary excitation in an inorganic semiconductor crystal. Wannier–Mott excitons are characterized by large Bohr radii (several tens of lattice constants) and relatively small binding energies (typically of the order of 10 meV).

TE–TM splitting

The energy splitting between optical modes having their electric field (TE) or magnetic field (TM) vectors in the plane of the cavity, respectively. The splitting is defined by Maxwell boundary conditions at the boundaries of the cavity. It strongly affects the polarization dynamics of exciton–polaritons, creating a kind of effective magnetic field acting upon polariton pseudospin (Stokes vector).

Su–Schrieffer–Heeger (SSH) model

This model predicts formation of spatially localized electronic states at the ends of molecular chains. It has generalizations for a large variety of one-dimensional systems.

Zak-phase

A topological number that refers to the Berry’s phase picked up by a particle moving across the Brillouin zone in a one-dimensional crystal.

Soliton

A solitary wave formed in a nonlinear system that preserves its shape when propagating. One can distinguish between bright and dark optical solitons characterized by a peak and a trough of intensity of the electromagnetic field. Bright solitons have been observed in polariton flows.

Polariton blockade

A formation of a polariton state with a fixed number of particles due to the nonlinear absorption of pumping laser light. It is expected to occur in the case of quasiresonant optical excitation where the efficiency of absorption of the laser light becomes strongly dependent on the occupation number of a polariton mode.

NP-hard problems

An important class of mathematical problems that are more complex than the most complex of NP problems, with NP standing for nondeterministic polynomial time. NP problems represent the set of decision problems solvable in polynomial time by a non-deterministic Turing machine.

Polariton superfluid

A polariton condensate demonstrating features of a superfluid such as quantized vortices, persistent currents, solitons, lack of scattering and viscosity, and Bogolyubov-like linear dispersion of excitations.

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Kavokin, A., Liew, T.C.H., Schneider, C. et al. Polariton condensates for classical and quantum computing. Nat Rev Phys 4, 435–451 (2022). https://doi.org/10.1038/s42254-022-00447-1

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