JQI Seminar

Quantum dots are often described as artificial atoms because they have discrete energy levels analogous to those of natural atoms. Solid state quantum dots (e.g. InAs in GaAs) can be extended from artificial atoms to artificial molecules by controlling the relative spatial proximity and orientation of a pair of quantum dots. These pairs of dots are called quantum dot molecules (QDMs) because coherent tunnel coupling between the individual quantum dots leads to the formation of molecular states analogous to those in diatomic molecules.

‘Circuit QED’ is the quantum theory of superconducting qubits strongly interacting with microwave photons in electrical circuits. It is the leading solid-state architecture in the race to develop large-scale fault-tolerant quantum computers, and is the only technology that has demonstrated quantum error correction that actually extends the lifetime of quantum information.  

In this era of noisy intermediate-scale quantum (NISQ) computing, systematic miscalibrations, drift, and crosstalk in the control of quantum bits can lead to a coherent form of error which has no classical analog. Such errors severely limit the performance of quantum algorithms in an unpredictable manner, and mitigating their impact is necessary for realizing reliable quantum computations.

Entanglement is the crucial ingredient of quantum many-body physics, and characterizing and quantifying entanglement in quantum dynamics is an outstanding challenge in today's era of intermediate scale quantum devices. Quantum simulators allow us to observe in quench dynamics the increasing complexity of the many-body wavefunction in evolution towards thermodynamic equilibrium, including regimes inaccessible to classical computation.

Einstein referred to the nonlocal collapse of the wave function as “spooky action at adistance”. John Bell later showed that the hidden-variable theories advocated by Einstein wereinconsistent with the predictions of quantum mechanics. This distinction between quantum andclassical behavior is not limited to microscopic particles, and Bell’s inequality can be violated bymacroscopic systems as well. We recently showed that a photon number state incident on abeam splitter will produce two output states whose phases are entangled [1]. We also showed

In his second week of residence at the University of Maryland, College Park, Prof. Srednicki will expand his portrait of thermalization of many-body quantum systems by introducing and explaining the eigenstate thermalization hypothesis, entanglement entropy, out-of-time-order correlations and quantum Fisher information.

In recent decades, artificial quantum "materials" built from ultracold atoms, ultracold molecules, and light have enabled the exploration of a range of phenomena of relevance to condensed matter physics, as well as the realization of entirely new states of matter with no direct analogs.

In 1962 Josephson predicted that an electric current can flow with no applied voltage through a thin insulating layer separating two superconductors. Since then, such "Josephson junction" has become has become the routinely used in many quantum electronic circuits (squids magnetometers, parametric amplifiers, superconducting qubits,...) and its use in the Volt metrology has helped reshape the International System of Units around quantum effects.

The physics of quantum matter is rich with spectacular excited-state and nonequilibrium effects, but many of these phenomena remain poorly understood and, consequently, technologically unexplored. My group’s research, therefore, focuses on how quantum systems behave, particularly away from equilibrium, and how we can harness these effects.

Understanding how and when closed quantum systems lose or retain coherence is a central intellectual and practical question in quantum science. In rare cases, such as collisional narrowing or environment assisted tunneling, random processes can enhance coherence processes. In this talk, I will present a new addition to this list—the quasi-periodic lattice described by the Harper-Hofstadter (HH) model in a highly-elongated tube geometry, by showing that the dynamics can be immune to environmental noise.