Spring 2023

Dissertation Committee Chair: Mohammad Hafezi

Committee: 

Abstract: I will discuss mesoscopic topological superconductors that can be used to realize quantum impurity models with orthogonal or symplectic symmetries. The first one uses a topological superconductor that hosts many (M>2) Majorana zero modes. Such an "M-Majorana island" coupled to normal metal leads realizes a novel type of topological Kondo effect, where the effective impurity "spin" transforms under the orthogonal group SO(M) stemming from the non-local topological ground state degeneracy of the island.

Strong light-matter coupling in optical cavities can alter the dynamics of molecular and material systems resulting in polaritonic excitation spectra and modified reaction pathways. For strongly coupled photon modes close in energy to nuclear vibrations the Cavity Born Oppenheimer Approximation (CBOA) in the context of quantum-electrodynamical density functional theory (QEDFT) has been demonstrated to be an appropriate description of the coupled light-matter system.

Abstract: We construct a Pauli stabilizer model for every Abelian topological order that admits a gapped boundary in two spatial dimensions. Our primary example is a Pauli stabilizer model on four-dimensional qudits that belongs to the double semion (DS) phase of matter. The DS stabilizer Hamiltonian is constructed by condensing an emergent boson in a Z4 toric code. We show that the construction of the DS stabilizer Hamiltonian generalizes to all twisted quantum doubles (TQDs) with Abelian anyons.

Abstract: Understanding the Hubbard model is crucial for investigating various quantum many-body states and its fermionic and bosonic versions have been largely realized separately. Recently, transition metal dichalcogenides heterobilayers have emerged as a promising platform for simulating the rich physics of the Hubbard model. In this work, we explore the interplay between fermionic and bosonic populations, using a WS₂/WSe₂ heterobilayer device that hosts this hybrid particle density.

While quantum walk frameworks make it easy to design quantum algorithms, as evidenced by their wide application across domains, the major drawback is that they can achieve at most a quadratic speedup over the best classical algorithm.  In this work, we generalise the electric network framework – the most general of quantum walk frameworks, into a new framework that we call the multidimensional quantum walk framework, which no longer suffers from the aforementioned drawback, while still m

Despite much work on quantum algorithms, there are few examples of practically relevant computational tasks that are known to admit substantial quantum speedups for practical instance sizes after all hidden costs and caveats are considered. Portfolio optimization (PO) is a practically important problem that can be solved via Quantum Interior Point Methods (QIPMs) via a standard mapping to a Second-Order Cone Programs (SOCP). Preliminary numerical evidence in prior literature was consistent with an asymptotic quantum speedup. But will this solution be practical?

Abstract: Excitons are composite Bosons formed by pairing electrons and holes in a crystal.The idea that excitons might Bose condense dates to the 1960’s but has often been surrounded by controversy. My talk will focus on the important lessons learned

about exciton condensates from work on two-dimensional electron systems in the

quantum Hall regime, starting around twenty years ago, and on new opportunities

Interacting fermionic systems can model real world physical phenomenon directly. Many people are working on finding efficient and practical ways to determine properties of these quantum simulators. Specifically, estimating correlation functions, that reveal important properties such as coulomb-coulomb interaction strength and entanglement spreading, is a crucial goal. The well know classical shadows formalism allows one to find linear properties of a quantum state by reusing outcomes from simple basis measurements.