Turbulence and superfluidity in atomic Bose-Einstein condensates
Dissertation Committee Chair: Daniel Lathrop
Committee:
Ian Spielman
Nathan Schine
Thomas Antonsen
Johan Larsson (Dean’s Rep)
Macroscopic quantum motion of a nanogram-scale object
Abstract: I will describe measurements of individual phonons in a 1 ng body of superfluid helium. When this body is in equilibrium, its phonon correlations are consistent (up to 4th order) with a thermal state of mean occupancy ~ 1. This purity is preserved even when the mode is driven to a coherent state with an amplitude corresponding to ~100,000 phonons. I will describe how these results can be used to constrain nonlinear extensions of quantum mechanics, and to distribute entanglement over kilometer-scale optical fiber networks.
Total functions exhibit exponential quantum advantage — albeit in a parallel universe
We construct a total function which exhibits an exponential quantum parallel query advantage despite having no sequential query advantage. This is interesting for two reasons: (1) For total functions an exponential sequential query advantage is impossible, and was conjectured to not be possible in the parallel setting by Jeffery et al (2017)— our result refutes this conjecture.
Harnessing Temporal Entanglement for Quantum Many-Body Dynamics
The dynamics of quantum many-body systems out-of-equilibrium are pivotal in various fields, ranging from quantum information and the theory of thermalization to impurity physics. Fundamentally, the numerical study of larger quantum systems is challenging due to the exponential number of parameters necessary to describe the wavefunction. If their entanglement is low, wavefunctions can be approximated with relatively few parameters using tensor networks. Since equilibrium wavefunctions have low entanglement, this makes computations viable.
Evaluating the security of CRYSTALS-Dilithium in the quantum random oracle model
In the wake of recent progress on quantum computing hardware, the National Institute of Standards and Technology (NIST) is standardizing cryptographic protocols that are resistant to attacks by quantum adversaries. The primary digital signature scheme that NIST has chosen is CRYSTALS-Dilithium. The hardness of this scheme is based on the hardness of three computational problems: Module Learning with Errors (MLWE), Module Short Integer Solution (MSIS), and SelfTargetMSIS. MLWE and MSIS have been well-studied and are widely believed to be secure.
Precision chemistry with ultracold molecules
Abstract: Over the past few decades, concurrent advances in experimental techniques in both quantum information science (QIS) and physical chemistry have enabled unprecedented control over simple molecules, both in terms of their lab-frame motions and their internal quantum states. In this talk, I will discuss the potential for these well-controlled molecules to advance two fundamental areas of physical chemistry: structure and dynamics.
The Quantum Age: From Atomic Clocks to Quantum Computers
Abstract: The last few years have seen a remarkable development in our ability to control many neutral atoms individually, and induce controlled interactions between them on demand. This progress ushers in a new era where one can create highly entangled states, overcome certain limits of quantum measurements using entangled states, or study quantum phase transitions. I will present results on atomic arrays containing hundreds of individually trapped atoms, and first steps towards quantum computation with error detection and correction.
Pairs and Loners in an Attractive Hubbard Gas
Abstract: The Hubbard model of attractively interacting fermions provides a paradigmatic setting for fermion pairing, featuring a crossover between Bose-Einstein condensation (BEC) of tightly bound pairs and Bardeen-Cooper-Schrieffer (BCS) superfluidity of long-range Cooper pairs, and a "pseudo-gap" region where pairs form already above the superfluid critical temperature. We directly observe the non-local nature of fermion pairing in a Hubbard lattice gas, employing spin- and density-resolved imaging of ∼1000 fermionic 40K atoms under a bilayer microscope.
Interferometric measurements of anyon braiding in the fractional quantum Hall regime
Abstract: A basic tenet of quantum theory is that all elementary particles are either bosons or fermions. Ensembles of bosons or fermions behave differently due to differences in their underlying quantum statistics. Starting in the early 1980’s it was theoretically conjectured that excitations that are neither bosons nor fermions may exist under special conditions in two-dimensional interacting electron systems. These unusual excitations were dubbed “anyons”.
One-shot quantum information theory and quantum gravity
The unification of quantum mechanics and gravity is a major outstanding goal. One modern approach to understanding this unification goes by the name ``holography’’, in which gravity can be understood as an emergent description of some more fundamental, purely quantum mechanical system. In this talk I will describe some recent results in holography that elucidate how this emergence works. A starring role will be played by one-shot quantum information theory.