The dawn of the era of layered quantum materials

The Nobel Prize in Physics 2022, awarded “for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science”, has spurred significant progress in quantum technology applications.

Researchers at the Graphene Flagship Partner University of Cambridge, in collaboration with University of Technology Sydney (Australia), have published a perspective outlining the potential of layered materials for quantum technologies.

The special characteristics of layered materials

Layered materials have unique optical, electronic, magnetic, thermal, and mechanical characteristics, and have already demonstrated their potential as scalable components for quantum light sources that emit light in a controlled manner at the quantum level, photon detectors, nanoscale sensors and in the field of quantum simulations.

Layered materials have special electronic properties that enable the creation of qubits – the fundamental units of quantum information, analogous to the classical bits (0s and 1s) in conventional computing. The properties of these qubits can be used for quantum computing, sensing and communications. By leveraging the quantum behaviour of layered materials, such as their ability to generate and manipulate single photons, one can develop efficient components for quantum communication networks, including sources, detectors and modulators. Layered materials can be integrated with optical waveguides and cavities to manipulate and control the flow of photons at the quantum level. Layered materials are also ideal for secure communication and encryption protocols, such as quantum key distribution (QKD) platforms, which are immune to eavesdropping.

Focusing on single-photon emitters

Currently, a large portion of research on the application of layered materials to quantum technology focuses on single-photon emitters. These are important because they serve as sources of individual photons and, if endowed with spins, they can work as optically active qubits. By utilising the interaction between qubits and photons, optically active qubits allow for the transfer, manipulation and control of quantum information using light. For example, they allow the transfer of quantum states from one qubit to another qubit, even if they are physically separated.

“For long-distance quantum communication and distributed quantum computing, you want to connect two locations that are kilometres or even thousands of kilometres apart. This task is taken by photons that carry quantum information between the two quantum processors,” explains Alejandro R.-P. Montblanch, from Graphene Flagship Partner University of Cambridge.

One of the most well-known examples of single-photon emitters is diamond with impurities. When carbon atoms in diamond are substituted with nitrogen, it gives rise to unique optical and spin properties, including the ability to emit single photons. Other single photon emitters are layered quantum materials, which include semiconductor transition-metal dichalcogenides (TMDs) – such as WSe₂, WS₂, MoSe₂, MoS₂ and MoTe₂ – hexagonal boron nitride (hBN), graphene, heterostructures, InSe, GaSe and layered Janus materials (WSeS, MoSeS).

hBN is interesting because it can operate at room temperature, it can emit photons ranging from infrared to ultraviolet, and it hosts controllable spins for developing new quantum sensors or quantum repeaters. Various techniques can be employed to generate single-photon emitters in TMDs and hBN. For instance, these can be created by placing the layered material on nanopillars, indenting the layered material using an atomic-force microscope, bombarding the material with helium ions, generating defects, or stacking layered materials with a specific angle to create a moiré pattern.

An outlook to the future

The large number of layered materials contain all the necessary components to create fully integrated quantum-photonic devices, including optically active qubits and single-photon detectors. The reliable generation of single-photon emitters is still a challenge but once achieved, the next steps would involve studying their spin properties of these photons and enhance coherence times, which determine how long the spin states can be preserved. Longer coherence time in quantum systems opens the possibility to use these spin states for data storage (memory). 

One advantage of using TMDs is that the coherence times can potentially be longer than other material systems, such as quantum dots. Combining hBN with advances in meta-optics can lead to the development of systems that can manipulate light on a single chip and quantum microscopy with extremely high resolution.

“Rapid progress in this field still requires the exploration of new synthesized materials that can harness quantum properties more feasibly and in a scalable manner,” points out Mete Atatüre from Graphene Flagship Partner University of Cambridge.

“The promise of layered materials in the context of quantum technologies can be now realised due the progress made in the last decade on the scalable synthesis and processing of TMDs and h-BN matching the quality of mechanically exfoliated flakes. Also, the stacking of these materials to conform homo- and heterostructures is reaching maturity and will enable the design of a new generation of novel architectures leading to quantum optoelectronic and spintronic devices as well as quantum sensors. The operation of the 2D-Pilot line, driving the laboratory scale research into foundry environment, will undoubtly contribute to the success of these materials as building blocks in the development of quantum technologies,” says Mar Garcia-Hernandez, Leader of the Graphene Flagship’s Enabling Materials Work Package.

Andrea C. Ferrari, Science and Technology Officer of the Graphene Flagship and Chair of its Management Panel, adds: “This perspective shows the promise of layered materials for quantum technologies and seals the link between the Graphene and Quantum Flagship. This will also fuel interest in the Innovative Materials for EU partnership, of which layered materials research is an integral part.”

Reference

Alejandro R.-P. Montblanch, Matteo Barbone, Igor Aharonovich, Mete Atatüre and Andrea C. Ferrari. Layered materials as a platform for quantum technologies. Nature Nanotechnology (2023)