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Quantum photonics with layered 2D materials

Abstract

Solid-state quantum devices use quantum entanglement for various quantum technologies, such as quantum computation, encryption, communication and sensing. Solid-state platforms for quantum photonics include single molecules, individual defects in crystals and semiconductor quantum dots, which have enabled coherent quantum control and readout of single spins (stationary quantum bits) and generation of indistinguishable single photons (flying quantum bits) and their entanglement. In the past 6 years, new opportunities have arisen with the emergence of 2D layered van der Waals materials. These materials offer a highly attractive quantum photonic platform that provides maximum versatility, ultrahigh light–matter interaction efficiency and novel opportunities to engineer quantum states. In this Review, we discuss the recent progress in the field of 2D layered materials towards coherent quantum photonic devices. We focus on the current state of the art and summarize the fundamental properties and current challenges. Finally, we provide an outlook for future prospects in this rapidly advancing field.

Key points

  • 2D materials host quantum emitters with strong light–matter interaction that can be integrated into on-chip devices.

  • Some 2D quantum emitters have an intrinsic spin degree of freedom that can be harnessed for spin–photon entanglement.

  • The ease with which 2D materials can be transferred onto photonic circuits to create hybrid devices provides new opportunities for scalable quantum photonic devices.

  • While quantum emitters in several 2D materials have been successfully identified, there remain challenges to building functional quantum technologies.

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Fig. 1: SPEs in WSe2.
Fig. 2: WSe2 SPEs in heterostructure devices.
Fig. 3: Moiré-heterostructure-based single-photon emitters.
Fig. 4: hBN-based single-photon emitters.
Fig. 5: A development timeline of quantum photonics platforms.

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Acknowledgements

The authors acknowledge funding from the European Union’s Horizon 2020 research and innovation programme (grant nos. 820423, 862721 and 965124), the ERC (no. 725920), the Academy of Finland (grants nos. 314810, 333982, 336144 and 336818), Aalto Centre of Quantum Engineering, the China Scholarship Council, the EPSRC (EP/P029892/1; EP/S000550/1; EP/S000550/1) and the Leverhulme Trust (RPG-2019-388). M.B.-G. thanks the Royal Society for a University Research Fellowship. B.D.G. was supported by a Wolfson Merit Award from the Royal Society and a Chair in Emerging Technology from the Royal Academy of Engineering. Z.S. thanks the other Aalto group members who initiated this Review’s writing that was later completely led by B.D.G.

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Supplementary information

Glossary

Spectral diffusion

Changes in the energy levels of an emitter due to electrostatic noise in the emitter’s environment.

Blinking

Random switching of bright and dark states of the emitter.

Transform limit

The ideal coherence limit: T2 = 2T1, where T2 and T1 are the emitter’s coherence time and lifetime, respectively.

Fine-structure splitting

(FSS). Splitting of exciton energy levels caused by spin interactions and/or wavefunction asymmetry.

Dark (free) exciton

In a dark exciton, the spins of the electron and the hole are parallel and spontaneous emission is forbidden due to spin momentum conservation.

DC Stark tuning

Tuning of emission spectra using an external electric field.

Plasmonic cavities

Cavities where the light is enhanced by the interaction of surface plasmons.

Purcell enhancement

Environmental enhancement of the light emission rate of a quantum system, typically caused by a resonant cavity.

Slot waveguide

A waveguide, where light is confined between two slabs of high-refractive-index materials.

Interlayer excitons

Electron–hole Coulomb bound states between electrons and holes spatially separated in different monolayers.

Debye–Waller factor

Describes the magnitude of thermal vibrations in a crystalline lattice and is used as a measure for the structural disorder of material.

Autocorrelation measurements

Second-order correlation measurement used to measure the time delay between two successive photons.

Cross-correlation measurements

Correlation measurement of two different signals.

Fermi–Hubbard model

Interaction model of fermions in a lattice.

Bose–Hubbard

Interaction model of bosons on a lattice.

Hong–Ou–Mandel interference

This bosonic interference describes the situation where two photons approach a 50/50 beam splitter from different input ports. If the photons are indistinguishable and they enter the beam splitter at the same time, both photons will exit together in a superposition from the output ports of the beam splitter.

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Turunen, M., Brotons-Gisbert, M., Dai, Y. et al. Quantum photonics with layered 2D materials. Nat Rev Phys 4, 219–236 (2022). https://doi.org/10.1038/s42254-021-00408-0

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