Abstract
The behavior of quantum systems across scale and implementation is shaped by three common constraints: how the constituents interact, how states can be steered and probed, and how decoherence competes with coherent dynamics. I will illustrate these levers with two experimental case studies, one emphasizing fundamental many-body physics and the other focused on device engineering.
First, atoms offer rich internal structures and highly tunable pairwise interactions. A dilute quantum-degenerate gas held in ultra-high vacuum combines configurability, large sample sizes in the tens of thousands, and excellent isolation from the environment. As coupling to external baths is strongly suppressed versus solid-state settings, we used an ultracold ensemble of highly magnetic dysprosium to study intrinsic quantum thermalization. One central result is an adiabatic transport protocol that cycles the contact interaction via magnetically tuned Feshbach resonances to adiabatically connect a ladder of increasingly excited metastable many-body states. The protocol exploits the integrable eigenstate structure to avoid mixing with unstable cluster states. Contrary to contemporary expectations, the long-range dipole-dipole repulsion of dysprosium, two orders of magnitude stronger than alkali atoms and naively expected to break integrability, instead stabilizes the gas across all contact strengths. This finding opens a new regime for studying the onset of chaos in near-integrable systems.
At the opposite extreme, superconducting circuits encode quantum information in collective electromagnetic modes of a macroscopic number of Cooper pairs. These circuits permit fast, high-fidelity operations but face practical scaling limits such as cryogenic wiring and thermal load. Optical fibers are attractive for scaling because they are compact, thermally insulating, and low-loss. Coherent microwave-optical transduction is therefore central to heterogeneous and distributed quantum architectures. Engineering efficient photon-photon coupling across five orders of magnitude in energy is a formidable task. To meet this challenge, we integrate second-order-nonlinear lithium tantalate photonic waveguides and high-kinetic-inductance niobium nitride superconducting circuits, enabled by semiconductor fabrication technologies. On-chip miniaturization and mode engineering facilitate cavity-enhanced electro-optic interactions, resulting in the circuit analog of optomechanical dynamical backaction. Concurrently, parasitic coupling to the electromagnetic and substrate phonon baths must be carefully managed. I will discuss progress toward an all-optical cryogenic microwave source envisioned to alleviate the cryostat wiring bottleneck.
Opportunities to endow analog quantum simulation with closed-loop control and apply integrated technologies to digital quantum computing based on neutral atoms will be highlighted.
Wil Kao received his Ph.D. from Stanford University, where he investigated quantum simulation using dipolar quantum gases under the supervision of Prof. Benjamin Lev. He is currently a Postdoctoral Researcher at the Laboratory of Photonics and Quantum Measurements at EPFL, working with Prof. Tobias Kippenberg on enabling technologies leveraging on-chip-integrated solid-state circuits for quantum networks and hybrid quantum systems. Wil additionally holds a B.A.Sc. in Engineering Science from the University of Toronto.