Talk Title#1 : Memory and optimization with multimode cavity QED

Speaker#1: Brendan Marsh

Abstract#1 : Quantum systems are driving a revolution in computing and information theory. Driven-dissipative quantum systems, which are both pumped by an external source and are open to environmental interactions, have not been explored as a computational resource as fully as their closed counterparts. In this talk, I will describe how a driven-dissipative system is realized by coupling ultracold atoms to a multimode optical cavity and how it can perform various computational tasks. Through a combination of unitary and dissipative dynamics, the system can learn and recognize arbitrary sets of patterns, an ability known as associative memory, and also functions as a heuristic solver for (NP hard) Ising optimization problems. These functionalities can be understood in terms of semiclassical theories that describe the transition to a superradiant ordered state, which encodes a learned pattern or a solution to an Ising problem. While a fully quantum description remains intractable, experimental progress will be discussed that demonstrates the required ingredients for near-term realization.

Talk title #2: Transverse-Field Ising Dynamics by Rydberg Dressing in a cold atomic gas

With recent progress on building large and controllable quantum systems, we are on the cusp of harnessing these systems for quantum computation and metrology. Optically controlled interactions are a necessary tool to implement computation and metrology schemes in a system of cold atoms. In this talk, we will present a realization of long-range optically-controllable Ising interactions in a cold gas of cesium atoms by Rydberg dressing. By adding microwave coupling between the clock states we emulate the transverse-field Ising model and detect dynamical signatures of the paramagnetic-ferromagnetic phase transition. We will discuss current progress towards producing spin squeezing by using local and dynamical control of interactions. Finally, we will describe prospects of encoding a quantum algorithm in a hardware-efficient way in this system.

Bio: Brendan Marsh is a Ph.D. student in Professor Benjamin Lev’s research group at Stanford University. He investigates light-matter interactions in many-body quantum systems and explores their use as a computational resource. His work more generally includes experimental quantum optics and theoretical methods to describe open quantum systems. He received a master’s degree in applied mathematics and theoretical physics from the University of Cambridge in 2018 and a B.S. in physics and mathematics from the University of Missouri in 2017.

Bio: Ognjen Marković is a physics Ph.D. candidate in the Schleier-Smith lab at Stanford University. He is working on a cold atom experimental platform with applications ranging from quantum simulation to quantum metrology. He obtained his B.A. and M.Sci. degrees in Natural Sciences at the University of Cambridge.