Friday Quantum Seminar

We derive a family of optimal protocols, in the sense of saturating the quantum Cramér-Rao bound, for measuring a linear combination of d field amplitudes with quantum sensor networks, a key subprotocol of general quantum sensor networks applications. We demonstrate how to select different protocols from this family under various constraints via linear programming. Focusing on entanglement-based constraints, we prove the surprising result that highly entangled states are not necessary to achieve optimality for many problems.

In this talk, I will discuss chaotic billiard systems subject to a rapid periodic driving force, with driving frequency ω. Classically, the energy of such systems changes by small, effectively random increments associated with collisions with the billiard wall, leading to a random walk in energy space, or “energy diffusion.” I will present a Fokker-Planck description of this process. This model displays several notable features, including a 1/ω² scaling of the energy absorption rate, and (in certain special cases) an exact analytical solution.

Recent years have seen the development of isolated quantum simulator platforms capable of exploring interesting questions at the frontiers of many-body physics. We describe our platform, based on a chain of Ytterbium ions in a linear trap, and describe its capabilities, which include long-range spin-spin interactions and single-site manipulation and readout. We then describe some recent studies undertaken with this machine, focusing on two.

The development of spin qubits with long coherence times for quantum information processing requires sources of spin noise to be identified and minimized. Although microwave-based spin control is typically used to extract the noise spectrum, this becomes infeasible when high frequency noise components are stronger than the available microwave power. Here, we introduce an all-optical approach for noise spectroscopy of spin qubits based on Raman spin rotation using Carr-Purcell-Meiboom-Gill (CPMG) pulse sequences.

This short talk provides a snapshot of opportunities in quantum science, technology, engineering, and mathematics (qSTEM) at the University of Maryland College Park (UMD). The UMD quantum ecosystem consists of seven quantum institutes, five quantum-adjacent institutes, and approximately 100 faculty, split 55/45 between theory and experiment. I organize the ecosystem into subfields: each subfield is described, and its corresponding faculty is listed. 

Pizza and drinks served after the talk.  This talk will start at 12:10 p.m.