The Quantum Semiconductor Systems group studies the behavior of electrons confined in reduced dimensional systems subject to strong mutual interactions. Researchers in the Quantum Semiconductor Systems group use a variety of techniques including semiconductor growth by molecular beam epitaxy (MBE), nanofabrication and low-temperature transport to explore this exciting field. MBE is a process to fabricate crystalline semiconductor heterostructures for the study of novel physical properties and solid-state device technology. In an MBE system we can grow heterostructures of dissimilar materials with atomic monolayer resolution. This allows us to explore the properties of strongly interacting electrons in two dimensions. We also exploit the nanofabrication facilities at the Birck Nanotechnology Center to further confine electrons in 1D (quantum wires) and 0D (quantum dots) structures. While these reduced dimensional systems exhibit many emergent phenomena due to collective behavior, they also hold promise as platforms for quantum computing.  The Quantum Semiconductor Systems group uses electrical transport experiments at temperatures down to T=10mK and magnetic fields up to 15Tesla to interrogate the samples we create. We also use MBE to pursue novel light-emitting sources in the Al(In)GaN heterostructure system. You will find brief descriptions of our ongoing projects below.

Quantum Computing with Majorana Fermions in Hybrid Semiconductor/Superconductor Systems

Recently we have launched Station Q Purdue - signifying our strong collaboration with Microsoft Research Station Q.  We are constructing a new deposition system that combines MBE growth of high spin-orbit coupling III-V semiconductors with superconducting metals to engineer hybrid materials capable of hosting Majorana fermions.  We actively collaborate with the experimental groups in Copenhagen, Delft, and Sydney in this effort. We anticipate that our new system will be operational in the summer of 2016.  Read more

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Non AbelianNon-Abelian Phases in the Fractional Quantum Hall Regime

The fractional quantum Hall effect (FQHE) occurs in a two-dimensional electron gas (2DEG) subjected to a perpendicular magnetic field at low temperature. It is now understood to arise from strong electron-electron interactions. In transport experiments the FHQE is characterized by Hall resistance quantized to rational fractional values of h/e2 and vanishingly small longitudinal resistance. Quasi-particle excitations in the FQHE are called anyons.  Read more

Engineering Heterostructures for High Fidelity Spin Qubits

Nanostructures such quantum dots fabricated on modulation-doped AlGaAs/GaAs heterostructures are widely used in spin-based approaches to quantum computing. Charge noise in these devices, however, limits gate fidelity. A quiet electrostatic environment is therefore essential for further progress.  Read more

Image courtesy of Ferdinand Kuemmeth.

2DEG-main-newUltra-High Mobility 2DEGs and 2DHSs in GaAs Grown by Molecular Beam Epitaxy

A major thrust in the Quantum Semiconductor Systems group is growth of extremely high quality GaAs/AlGaAs heterostructures. One metric of quality is 2D mobility, which can now exceed 30 x 106 cm2/Vs at low temperatures. At low temperature mobility is limited by imperfections in the grown sample. Imperfections include intentionally introduced charged impurities, unintentional background charged impurities and structural defects.

Our efforts are focused in 3 areas: improved MBE vacuum conditions, source material purity, and heterostructure design.  Read more

Novel Devices with Non-Polar m-plane GaN/AlGaN and Lattice-Matched AlInN/GaN heterostructures

Our work in the III-Nitride material system is focused on exploiting its unique physical properties to produce novel light sources based on intersubband transitions. Due to the large conduction band offsets available in Al(In)GaN/GaN heterostructures, intersubband transitions can span the technologically important near-IR (~1.5microns) to far-IR (~100microns) spectral range.  Read more