ENTANGLEMENT COMPLEXITY OF QUANTUM STATES, DYNAMICS AND QUANTUM COMPUTATION

Speaker: Zhicheng Yang

When: April 1, 2019 (Mon), 02:15PM to 03:15PM (add to my calendar)
Location: SCI 352

This event is part of the PhD Final Oral Exams.

Examining Committee: Claudio Chamon, Andrei Ruckenstein, Anatoli Polkovnikov, Michael El-Batanouny, So-Young Pi

Abstract: Quantum entanglement has become the key notion bridging originally distinct elds of research over the last decade, namely, quantum information and computation, condensed matter physics, and quantum gravity. Previous studies on quantum entanglement have largely focused on the entanglement entropy, which quanties the amount of entanglement. However, a natural question arises: is there additional information of a quantum state that is not captured by the entanglement entropy alone? For ground states of gapped Hamiltonians, this question has been answered in the armative. In this dissertation, I extend this idea to study highly entangled states typically having volume law entropy, and demonstrate that there is indeed much richer information on the complexity of a quantum state beyond the entanglement entropy. In the rst part, I study the entanglement spectrum of highly entangled states corresponding to highly excited eigenstates of non-integrable Hamiltonians, timeevolved states after a quantum quench with Hamiltonians exhibiting dierent dynamical phases, and random unitary circuits consisting of random braids of non-Abelian anyons. I demonstrate that the entanglement spectrum is able to capture the degree of randomness of a quantum state, which we call the entanglement complexity.

In the context of scrambling, this quanties the degree of randomness produced by scrambling beyond entropic diagnostics. Our understanding of quantum entanglement in condensed matter systems and high energy physics have largely beneted from the eld of quantum computation. In the second part of the dissertation, I present two examples of novel platforms for quantum computation using state-of-the-art experimental technologies. I demonstrate how one can use hybrid quantum-classical architecture to solve computational problems based on an optimal variational ansatz of the evolution protocol. I also present a hierarchical architecture of constructing logical Majorana zero modes which can be used for demonstrating non-Abelian braiding statistics experimentally.