Coherence protection of spin qubits in hexagonal boron nitride
A 2D material is one that consists of a single layer of atoms that can exist in isolation. Graphene was the first to be experimentally realised, but there is now an extensive list of 2D materials, including those with metallic, insulating, semiconducting and even superconducting properties. This provides a toolbox from which to mix and match different materials, and to combine them with different material platforms, to develop novel electronic and optoelectronic devices.
Hexagonal boron nitride (hBN) is one such material, which shares a similar crystal structure to graphene, but whereas the carbon atoms in graphene’s hexagonal lattice leads to semimetallic properties, the boron and nitrogen atoms leads to semiconducting behaviour with a wide band gap, which makes it transparent to infrared, visible and most UV light. Defects within the otherwise perfect hexagonal lattice, such as missing or impurity atoms, modify the local electronic landscape and behave like “artificial atoms” and are conceptually similar to defects found in diamond, which is one area of focus of the Quantum Computing and Simulation (QCS) Hub (https://www.qcshub.org/diamonds). These defects are inherently quantum objects, which have discrete energy levels that can be addressed and manipulated using a combination of microwaves and light and can be thought of as quantum bits (qubits) that can be the building block for quantum information and sensing applications.
One of the key metrics for a qubit is the coherence time. This is a measure of how long a superposition of the states can exist before being destroyed by environmental fluctuations. In hBN, this coherence time is short compared to other qubit systems, due to magnetic noise from the nuclei of the boron and nitrogen atoms. However, this has been addressed in recently published work by researchers at University of Exeter, University of Cardiff, and Hitachi Cambridge Laboratory, which was supported by Partnership Resource Funding from the QCS Hub. In their paper, Ramsay and co-workers demonstrated that the coherence time can be extended by 150 times by engineering the microwave control signal. This result is particularly promising for sensing high frequency magnetic fields, where the 2D nature of hBN offers the potential for the sensor to be placed in close proximity, or even to be embedded within, the system of interest.
The full paper, Coherence protection of spin qubits in hexagonal boron nitride, is published in Nature Communications.
