Research

 

Semiconductor Quantum Dots for Quantum Computing

One of the grand challenges in science and technology today is to build a quantum computer that can perform computation tasks that are unsolvable by classical computers. Semiconductor quantum dots are a leading approach for the implementation of solid-state based quantum computing, as the coherence time of the qubits can be extremely long and various interactions, inherent to semiconductors, can be harvested to precisely control superposition and entanglement. Over the years, Jiang's group has carried out breakthrough research to develop basic building blocks for quantum computation and quantum communications using spin, charge, and other degree of freedoms of individual electrons, as well as photons in semiconductors. For example, the group recently has coherently manipulated and performed projective read-out of a novel qubit that is based on valley states of single electrons, as valley represents another quantum degree of freedom, complementary to that of charge and spin.

Valley QCJohn Dean Rooney OVG

Si Quantum Dot Device

Topological Excitations in Magnetic Tunnel Junctions

In recent years, it has been discovered that topology hidden inside certain materials can be excited electrically or magnetically, to design the next generation of electronics. Skyrmion, a nanoscale whirling magnetic pattern, is an example of such topological excitations in magnetic materials.  The magnetic tunnel junction is arguably the most promising spintronics device, developed in the recent years, for data storage, sensing, and logic computation.  Generally, two opposite ferromagnetic states are used to store binary data in the magnetic tunneling junctions. This experimental research develops new ways to create, probe, and manipulation the magnetic skyrmion states in the magnetic tunnel junctions.  The skyrmion-based magnetic tunnel junctions are expected to consume less energy, operate at a higher speed, and be more robust against material disorder.
   
skyrmion

Movie: electrically-induced skyrmion in a magnetic tunnel junction

 

Physics of Two-Dimensional Electron Systems

The objective is to gain a fundamental understanding of magnetic-field-induced delocalization and quantum phase transitions in correlated and disordered two-dimensional electronic systems.  Recent experiments employ electrically detected NMR (nuclear magnetic resonance) and ESR (electron spin resonance) to probe spin excitations of two-dimensional electrons in GaAs/AlGaAs and Si/SiGe heterostructures with two quantized subbands.  The research has revealed a rich phase diagram with intriguing topologies and potentially new electronic phases due to the interaction of two energy levels with opposite spin and different orbital (i.e., subband) quantum numbers.  The group also conducts high-sensitivity thermodynamic measurements, as these measurements provide a means to probe the many-body ground state properties of the interacting charge carriers.

PRL Cover

 

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