DEPARTMENT OF PHYSICS DISSERTATION DEFENSE: Tony Zhang

Public Zoom Link:  https://stanford.zoom.us/j/94788288060?pwd=kEgJ70zwH4ca7IhmUiYWU8PQlAgakO.1

Password: Email physicsstudentservices [at] stanford.edu (physicsstudentservices[at]stanford[dot]edu)

Title:

Collective entanglement in Rydberg atom arrays: from dipolar interactions toward millimeter-wave cavity quantum electrodynamics 

Abstract:

Collective entanglement—entanglement shared across a many-particle quantum system—is a central resource for quantum metrology and computation. In this thesis, I present progress along two complementary, hardware-native approaches for engineering long-range, collective entanglement in Rydberg atom arrays. First, we use resonant dipolar interactions between Rydberg atoms to create Schrödinger's-cat–like entangled states, whose coherence we quantify with an interaction-based readout scheme robust to detection errors. That dipolar interactions alone, perhaps surprisingly, can produce collective entanglement is due to a deep resemblance to the celebrated one-axis twisting model consisting of all-to-all Ising interactions, which is known to dynamically generate cat states [1]. Second, I detail progress toward a complementary approach for generating scalable, nonlocal entanglement in atom arrays using cavity-mediated interactions at millimeter-wave frequencies. Superconducting millimeter-wave resonators offer orders-of-magnitude enhanced coherence in atom–light coupling versus their optical counterparts, as shown in pioneering experiments with atoms transiting a superconducting cavity [2]. Toward harnessing this strong coupling to engineer entanglement in atom arrays, I present a superconducting Fabry–Pérot cavity attaining a finesse of 5.8(1) × 10^7 providing sufficient transverse optical access for single-atom trapping and imaging [3]. I further discuss a near-term path for integrating this cavity with a cryogenic atom array to realize nonlocal, cavity-mediated entangling gates with projected fidelity above 98%. [1] Comparin, Mezzacapo, and Roscilde, Phys. Rev. Lett. 129, 150503 [2] Haroche, Rev. Mod. Phys. 85, 1083 [3] Zhang et al, Phys. Rev. Applied 24, L041001