Our group develops measurement tools, methods, and theory that are required both for exploring quantum phenomena in new materials and devices and for harnessing these phenomena in sensing, computing, and metrology applications. We pursue a two-prong approach: we build unique measurement instruments for exploring QIS phenomena, and we use quantum phenomena for new measurement methods. The solid-state systems of interest include layered atomically-thin materials, topological materials, correlated oxides, atomic lattices assembled on these materials and crystal defects in wide-band semiconductors. All these materials platforms offer opportunities for quantum information science (QIS). The examples of QIS applications of interest here are the quantum anomalous Hall effect (QAHE) and solid-state quantum simulators.
The QAHE observed in magnetic topological materials or in Moiré heterostructures gives rise to the quantized Hall conductance without the need for any applied magnetic field. The development of electrical standards based on the QAHE directly supports main NIST mission of disseminating quantum-based standards.
Some of the most significant opportunities for quantum computations are the simulation of quantum systems: modeling the properties of assemblies of quantum constituents or particles that are the building blocks of modern and future materials relevant for electronics, chemical engineering and drug design. A promising intermediate-term solution is to build a physical system with controllable quantum components that can simulate these interacting systems directly - the approach known as analogue quantum simulation (AQS).
Some of our measurement and fabrication capabilities include:
Atomic-scale microscopy and spectroscopy of interfaces and devices for quantum materials characterization and nanoelectronics
A suite of the state-of-the-art custom designed scanning probe systems (scanning tunneling microscopy / spectroscopy (STM/S) and atomic force microscopy (AFM)) combined with transport characterization that operate in ultra-high vacuum, at ultra-low temperatures (down to 15 mK), and in ultra-high magnetic field (up to 15 T) environments. Supporting capabilities include in-situ material growth by molecular beam epitaxy and device fabrication with nano-stencil masks. The facility is used for fabrication and atomic scale characterization of devices built of 2D materials, topological materials and atom-assembled quantum systems.
Electron spin resonance (ESR) in STM for manipulation and fabrication of quantum states
STMs can be used to locally create and manipulate individual quantum states by applying a controlled stimulus, e.g. a voltage waveform combining dc, pulse or radiofrequency (RF), to the sample through the tip. Individual spin states can be manipulated and probed in electron-spin resonance (ESR)-STM setup by applying RF waveforms to the tip that flip/rotate spin and provide time-resoled spin state sensing. Electron wavefunctions can be controlled and modified by forcing movement of charges that creates quantum wells and barriers confining free carriers or by depositing and assembling ad-atoms. Our newest ultra-low temperature (down to 10 mK) system is designed to have all these capabilities.
Fabrication and characterization facilities for heterostructures built of atomically-thin materials.
Engineering quantum materials by stacking atomically thin layers is a new and exciting area of research. Moiré heterostructures built by stacking dissimilar or twisting similar two-dimensional (2D) van der Waals materials is a powerful materials platform for solid-state analog quantum simulators and the quantum anomalous Hall effect. All tools for device fabrications are available including layers stacking with a controlled angle in inert environment, cleaning and patterning by AFM, Raman characterization and a variety of lithography, deposition and etching tools in CNST NanoFab. Closed cycle cryostats and probe station are used for magneto-transport studies over a broad temperature range.
Spin-based metrology for atomic-scale defects
Atomic-scale defects are the fundamental entities responsible for a wide range of solid-state materials science and device engineering phenomena. Control and manipulation of defects is performed by exploiting the interaction of point defects with magnetic fields and the effect of that interaction on light and electrical current. The recent development of nitrogen-vacancy (NV) defects in diamond as a room-temperature, single-spin field sensors can address the needs to quantitatively characterize magnetic nanodevices relating materials properties and device geometry with fundamental spin transport physics. The unique properties of this defect including optical initialization and readout of the spin state and a long coherence time allow for room temperature measurements of magnetic field with a noise floor on the order of 10 nT/(Hz)1/2.