Physics Colloquia

Semiconductor spin qubits offer a unique opportunity for scalable quantum computation by leveraging classical transistor technology. This has triggered a worldwide effort to develop spin qubits, in particular, in Si and Ge based quantum dots, both for electrons and for holes. Due to strong spin orbit interaction, hole spin qubits benefit from ultrafast all-electrical qubit control and sweet spots to counteract charge and nuclear spin noise . In this talk I will present an overview of the state-of-the art in the field and focus, in particular, on recent developments on hole spin physics in Ge and Si nanowires, Si FinFETs, and Ge heterostructures.

In the recent years experiments have observed a plethora of unusual hadrons which do not conform to the usual paradigm of quark-antiquark mesons and three-quark baryons. They always contain both heavy and light quarks. I will discuss the very recent related experimental and theoretical developments regarding such “exotic” states — tetraquark and pentaquark hadronic molecules, doubly heavy baryons and most strikingly, a four quark state which is stable under strong interactions.

In the recent years experiments have observed a plethora of unusual hadrons which do not conform to the usual paradigm of quark-antiquark mesons and three-quark baryons. They always contain both heavy and light quarks. I will discuss the very recent related experimental and theoretical developments regarding such “exotic” states — tetraquark and pentaquark hadronic molecules, doubly heavy baryons and most strikingly, a four quark state which is stable under strong interactions.

The Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity described all superconductors until the 1986 discovery of the high-temperature counterpart in the cuprate ceramic materials. This discovery has challenged conventional wisdom as these materials are well known to violate the basic tenets of the Landau Fermi liquid theory of metals, crucial to the BCS solution. Precisely what should be used to replace Landau's theory remains an open question. The natural question arises: What is the simplest model for a non-Fermi liquid that yields tractable results. Our work builds[1] on an overlooked symmetry that is broken in the normal state of generic models for the cuprates and hence serves as a fixed point. The fixed point is quadratic and the only relevant perturbation is in the Cooper channel. However, the resultant superconducting state differs drastically[3] from that of the standard BCS theory. For example the famous Hebel-Slichter peak is absent and the elementary excitations are no longer linear combinations of particles and holes but rather are superpositions of composite excitations. Our analysis here points a way forward in computing the superconducting properties of strongly correlated electron matter.
[1] E. Huang, G. La Nave, P. Phillips, Nature Physics volume 18, pages511?516 (2022)
[2] PWP, L. Yeo, E. Huang, Nature Physics, 16, 1175-1180 (2020).
[3]J. Zhao, L. Yeo, E. Huang, PWP, Phys. Rev. B 105, 184509 ? Published 12 May 2022

Quantum Chromodynamics is fifty years old this year. I shall discuss the past, present and future of this remarkable theory
Please note unusual day, time and location