Spring 2022

Abstract: The bright emission observed in cesium lead halide perovskite nanocrystals (NCs) has recently been explained in terms of a bright exciton ground state, a claim that would make these materials the first known examples in which the exciton ground state is not an optically forbidden dark exciton.

Abstract: I will describe the theory of generalized hydrodynamics (GHD), which allows the dynamics of nearly integrable many-body quantum systems to be accurately modeled. GHD has two assumptions: the continuum approximation and local equilibration to the Generalized Gibbs ensemble (GGE). We use bundles of 1D Bose gases to test GHD and show that the theory works remarkably well for quite a long time after even very large trap quenches and even for as few as 10 atoms per 1D gas. We have also performed wavefunction quenches.

Abstract:Quantum computers have finally reached a level of complexity where real-time quantum error correction is possible. Current systems have shown an advantage using encoded qubits for some experiments, but no experiment has shown a decisive victory of encoded qubits over physical qubits. I will review the current state-of-the-art and then provide some lessons learned from adapting fault-tolerant quantum circuits to ion trap hardware.

Abstract: Quantum spin liquids are remarkable phases of matter in which quantum entanglement is, in a precise sense, truly long-ranged.  I will describe realization of quantum spin liquid correlations in recent experiments on pumped Rydberg atoms trapped in arrays of optical tweezers.  I will also describe how recent theories of quantum spin liquids in metallic states provide a description of photoemission observations in the mysterious “pseudogap” state of the cuprate high temperature superconductors.

Abstract: Materials are often used to manipulate and control photons.  Metamaterials -- judiciously engineered material structures -- have enabled scientists and engineers to construct platforms with unconventional material parameters, providing exciting opportunities for optical and microwave devices and components.

Abstract: We add non-linear and state-dependent terms to quantum field theory. We show that the resulting low-energy theory, non-linear quantum mechanics, is causal, preserves probability and permits a consistent description of the process of measurement. We explore the consequences of such terms and show that non-linear quantum effects can be observed in macroscopic systems even in the presence of de-coherence. We find that current experimental bounds on these non-linearities are weak and propose several experimental methods to significantly probe these effects.

Abstract: Tightly packed ordered arrays of atoms exhibit remarkable collective optical properties, as dissipation in the form of photon emission is correlated. In this talk, I will discuss the many-body out-of-equilibrium physics of atomic arrays, and focus on the problem of Dicke superradiance, where a collection of excited atoms synchronizes as they decay, emitting a short and intense pulse of light. Superradiance remains an open problem in extended systems due to the exponential growth of complexity with atom number.

Abstract: We find a fast non-adiabatic protocol for the creation of spin squeezed ground states in a spin-1 Bose condensate and experimentally generate those states near the quantum critical point between the polar and ferromagnetic quantum phases of the interacting spin ensemble. The method consists of a pair of controlled quenches of an external magnetic field, which has the same leading order dependence for the total time as the quantum optimal control method but is simpler and realizable.

An industry is emerging to develop practical applications of the quantum computing, communication and networking concepts that have emerged during the past 25 years.  We will hear of opportunities and challenges in this field from two industry leaders:

Abstract: In this talk I will study the extension of fault tolerance techniques to holographic quantum error correcting codes in the context of the ads/cft correspondence. I will seek to argue that the threshold here corresponds to that of the confinement/de confinement phase transition here, analogously to the situation in topological quantum error correcting codes based on Tqft’s.
Join Zoom Meeting
https://umd.zoom.us/j/4111099146
Meeting ID: 411 109 9146