Fall 2022

Abstract: Under suitable experimental conditions, some twisted graphene multilayers and transition-metal dichalcogenides become Chern insulators, exhibiting the anomalous quantum Hall effect and orbital magnetization due to spontaneous valley polarization. We study (theoretically) the interaction of a Chern insulator with circularly polarized light, originating from the optical Stark energy shift. The interaction energy contains an antisymmetric term that couples the helicity of incident light and the Berry curvature of the electronic system.

Committee:Prof. Christopher Monroe  (Chair)Prof. Ronald WalsworthProf. Donald YeungProf. Norbert LinkeProf. Christopher Jarzynski (Dean’s Representative)

Dissertation Committee Chair: Prof. Steven Rolston
Committee: 
Dr. Trey Porto – Advisor – Co-Chair
Dr. Gretchen Campbell
Dr. Victor Galitski
Dr. Thomas Murphy (Dean’s Representative)

Motivated by the recent progress of quantum chaos and quantum information scrambling, the growth of an operator under the Heisenberg evolution has attracted a lot of attentions. I will first introduce a recently proposed perspective on the operator growth problem from the Lanczos algorithm point of view and the associated “Krylov complexity”.

Topological mixed quantum states in or out of equilibrium can arise in open quantum systems. Their linear responses are generally non-quantized, even though quantized topological invariants can be defined. In this talk, I will present a real-time U(1) topological gauge field action capable of reconciling this paradoxical phenomenology. In addition to non-quantized linear responses, this action encodes quantized non-linear responses associated with mixed state topology.

A fundamental distinction between many-body quantum states are those with short- and long-range entanglement (SRE and LRE). The latter, such as cat states, topological order, or critical states cannot be created by finite-depth circuits. Remarkably, examples are known where LRE is obtained by performing single-site measurements on SRE states such as preparing the toric code from measuring a sublattice of a 2D cluster state.

Arrays of neutral atoms promise to enable a variety of goals across quantum science, including quantum information processing, metrology, and many-body physics. While there have been recent significant improvements in quantum control, coherence times, and entanglement generation, one outstanding limitation is the efficient implementation of dissipation or measurement.

Concepts from topology provide insight into wide ranging areas from fluid mechanics to quantum condensed matter physics. We studied the topology of ultracold 87Rb atoms in a highly tunable bipartite optical lattice, using a form of quantum state tomography, to measure the full pseudospin state throughout the Brillouin zone. We used this capability to follow the evolution of two topological quantities: the Zak phase and chiral winding number, after changing the lattice configuration.

Near-term quantum information processors will not be capable of quantum error correction, but instead will implement algorithms using the physical native interactions of the device. These interactions can be used to implement quantum gates that are often continuously-parameterized (e.g., by rotation angles), as well as to implement analog quantum simulations that seek to explore the dynamics of a particular Hamiltonian of interest.

Physics is a human activity. Doing hard science involves not only having ideas and taking data, but also convincing your peers by communicating your results in a clear fashion. In this talk, I will offer a bit of the editorial perspective from PRL on how scientific knowledge is established in papers. Our main topic will be the way papers are conceived, treated by editors, assessed by peers, and finally published.