A collage of three semiconductor qubits

The Eriksson Group in the Physics Department at the University of Wisconsin-Madison focuses on semiconductor quantum dot qubits, quantum computing and information, quantum measurement, nanostructure fabrication, thermal transport, semiconductor physics, and the interface between semiconducting and superconducting quantum science and technology.

Our work on quantum computing is focused on gate defined quantum dots in both silicon/silicon-germanium (Si/SiGe) heterostructures and metal-oxide-semicondutor (MOS) structures. We fabricate these quantum dots using cleanroom-based nano fabrication tools, including photolithography and electron beam lithography.  The lateral confinement in these quantum dots is provided by voltages applied to electrostatic gates, an approach that provides in-situ tunability of the device during experiments and measurement. Measurements are performed in dilution refrigerators with a base temperature of order 10 mK and in magnetic fields, when necessary, up to 14 T. We make use of precision electronics for ultra-low noise measurement of electronic properties, and qubit manipulation often involves changing gate voltages on time scales shorter than 100 ps.  Quantum measurement takes the form of charge sensing through integrated single-electron transistors and dispersive readout using the methods of circuit-QED.

These methods have enabled demonstrations of one and two qubit gates, single-shot qubit readout, and characterization of T1 and T2 coherence times for semiconductor qubits.

We are also interested quite generally in nanofabrication and the properties of those nanostructures in semiconductors.  These topics include (i) understanding the valley degrees of freedom in silicon qubits, quantum wells, and quantum dots, (ii) understanding thermal transport across interfaces in thin materials, and (iii) charge noise, how to measure it, and how to reduce it, especially through the use of novel dielectric materials.