JQI

Dissertation Committee Chair: Daniel Lathrop

Committee: 

Ian Spielman

Nathan Schine

Thomas Antonsen

Johan Larsson (Dean’s Rep)

Abstract: 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. (2) The exponential speedup emerges entirely from quantum algorithms being able to utilize parallelism more effectively than classical algorithms, making this a genuinely parallel phenomenon.

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.

Abstract: 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.

Abstract: 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.

Abstract: There is a rich connection between classical and quantum codes and holographic correspondence connecting 2d CFTs and abelian 3d Chern-Simons theories. In the 3d language the codes emerge as a way to parametrize condensable anyons. Upon condensation 3d topological field theory gives rise to 2d CFT at the boundary. This provides a way to construct 2d CFTs from codes - the so called "code CFTs." This construction of code CFT has a natural interpretation in terms of a CSS quantum code (defined in terms of the original classical code, defining the CFT).

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.

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.

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.

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”.