Quantum Materials & Engineering Group @ UD

Department of Physics & Astronomy/Department of Materials Science & Engineering


Technologies that harness quantum phenomena - known as quantum technologies - promise transformative potentials in the areas of computation, sensing, and communication. We seek to contribute to the development of quantum technologies via advancing the follwoing two frontiers:

  1. The study of quantum materials - materials that manifest collective quantum phenomena - which may provide platform for qubits or new information technology, and

  2. Engineering quantum systems, including hybrid quantum architectures and multi-qubits systems.

A key platform in our research are solid-state atomic qubits formed by defects in wide bandgap semiconductors, the most famous of which being nitrogen vacancy (NV) centers in diamond.

Our research is highly interdisciplinary, drawing on concepts and techniques from condensed matters (CM) physics, atomic/molecular/optical (AMO) physics, quantum information science (QIS), materials science and engineering, and nanotechnology and fabrication.

Probing quantum materials with NV quantum sensors

Quantum materials (QMs) are materials that display collective quantum phenomena in the constituent electrons or spins. They include high-temperature superconductors, low-dimensional materials, and topological materials. Due to their novel phenomena that are of interest for fundamental science and potential as hosts for robust qubits, QMs are on the forefront of condensed matter and material research.

Many of the exotic properties that make QMs interesting are also out of reach with exisiting probes. In this context, quantum sensing technology realized with nitrogen vacancy (NV) center in diamond has emerged as a powerful probe of QMs. Due to its ability to sense magnetic field with high spatial resolution over wide temperature and dynamic range, NV sensors enable the investigation of materials and devices in parameter space inaccessible to existing tools.

We are interested to apply NV quantum sensors to study correlated phenomena in a wide variety of quantum materials, as well as developing new tools for probing condensed matter and material science. We are particularly interested in 2D materials, materials for spintronics, and topological materials. In the following are examples of works along this direction.

Top: NV magnetic imaging of stray field from 7-layer exfoliated flake of Fe5GeTe2, showing room-temperature magnetism in thin flakes of 2D magnet. Bottom left: atomic force microscope image.

2D magnets

2D materials, also known as van der Waals or layered materials, can exist as atomically-thin monolayers. Given their 2D nature, they can display unusual macroscopic quantum effects, and also have the potential for engineering unique information processing capabilities. While a great number of 2D materials have been discovered in the last two decades, 2D materials with intrinsic magnetic ordering were only discovered in the last few years. The potential for drastic miniaturization of magnetic devices, the ability to create new capabilities via heterostructure, and the possibility to engineer new quantum phases make 2D magnets important systems for exploration.

At UD, we are studying 2D magnets by employing NV quantum sensors to detect magnetic field emanated by these materials. An example of work in this direction is in the following publication:

H. Chen*, A. Asif*, M. Whalen*, et al, arXiv:2110.05314 (2021).
(* equal contribution)

Imaging viscous flow of electrons in graphene

M.J.H. Ku*, T.X. Zhou* et al, Nature 583, 537 (2020).
(* equal contribution)

When the movement of electrons is dominated by their mutual collision (instead of relaxation by impurities or phonons), electrons can enter a novel transport regime in which they flow as a fluid with viscosity. In this work, we imaged electronic flow in graphene with NV quantum sensors. The figure displays such an image of current density. Here, magnitude is shown by the color and direction is shown by the arrows; the graphene channel outline is shownin red. The inset displays a linecut of the current density, showing a parabolic flow profile - known as Poiseuille flow - as a result of viscosity in the fluid.

Probing spin-torque oscillation in a magnetic insulator

H. Zhang*, M.J.H. Ku* et al, Phys. Rev. B 102, 024404 (2020).
(* equal contribution)

Spin-torque can drive magnetic oscillations in micro/nano magnetic structures. These spin-torque oscillators (STOs) provide a crucial building block for spintronic technologies. We developed a technology based on NV centers for probing STOs (panel a). We are able to map out spin-wave (SW) spectrum as a function of external magnetic field and applied current (b), and subsequently study SW dynamics. This technology embodies high spatial and spectral resolution not found in other tools, hence provide a much needed capability for advanced STO research.

Engineering quantum systems

The realization of quantum technologies demands the ability to generate quantum systems with desired properties and to exert fine control over their quantum states. This endeavor requires an integrated approach involving tools from material science, nanofabrication, and quantum information science.

We are interested in 1) engineering new quantum systems, including hybrid quantum architectures and multi-qubits systems, and 2) developing quantum control tools and capabilities. These efforts will involve solid-state atomic qubits in diamond, such as NV centers, as well as qubits hosted by other material platforms. Examples of works towards these directions include Kuate Defo et. al. J. Appl. Phys. 129, 225105 (2021) and M.C. Marshall et. al. Quantum Sci. Technol. 6, 024011 (2021).