Seminar Schedule

In 1976 Kroger and Reich established the existence of a low-lying, nuclear excited state in Th-229 that appeared to be accessible with laser technology. This discovery touched off a flurry of activity to perform laser spectroscopy of a nucleus, as a laser-accessible nuclear transition would provide a host of new technological and scientific applications. Despite this significant activity, to date, no one has succeeded in actually performing laser spectroscopy on the nucleus. I will discuss our efforts to do exactly this.

In Fall 2019, a team at Google made the first-ever claim of "quantum computational supremacy"---that is, a clear quantum speedup over a classical computer for some task---using a 53-qubit programmable superconducting chip called Sycamore. In Fall 2020, a group at USTC in China made a claim of quantum supremacy, using "BosonSampling" (a proposal by me and Alex Arkhipov in 2011) with 50-70 photons in an optical network. In addition to engineering, these accomplishments built on a decade of research in quantum complexity theory. This talk will discuss questions like: what exactly were the contrived computational problems that were solved? How does one verify the outputs using a classical computer? And how sure are we that the problems are indeed classically hard? I'll end with a proposed application for these sampling based quantum supremacy experiments that I've been working on: namely, the generation of certified random bits, for use (for example) in proof of-stake cryptocurrencies.

The quantum optical control of solid-state mechanical devices, quantum optomechanics, has emerged as a new frontier of light-matter interactions. Objects currently under investigation cover a mass range of more than 17 orders of magnitude - from nanomechanical waveguides to macroscopic, kilogram-weight mirrors of gravitational wave detectors. Extending this approach to levitated solids opens up complete new ways of coherently controlling the motion of massive quantum objects in engineerable potential landscapes. I will discuss recent experimental advances in quantum controlling levitated solids, including demonstrations of the motional quantum ground state of optically trapped nanoparticles in a room temperature environment. I will also discuss the perspective for such experiments to create superpositions of gravitational source masses. This addresses directly one of the outstanding questions at the interface between quantum physics and gravity, namely “what is the gravitational field generated by a quantum object?”.

The tremendous scientific opportunities presented by ultracold molecules have driven rapid progress in both the assembly of diatomic molecules from ultracold atoms and the direct cooling of diatomic and polyatomic molecules. Diatomic species have been magneto-optically trapped and sub-Doppler cooled and their collisions have been studied in several experimental systems, including magnetic traps and merged optical tweezers. The pioneering work that led advances in direct cooling began with Stark deceleration, buffer-gas cooling and loading of traps, buffer-gas beam sources, mechanical slowing, and a variety of electromagnetic trapping and cooling mechanisms. As the field of cold and ultracold molecules has grown, polyatomic molecules have attracted new focus as potential novel quantum resources that have distinct advantages (and challenges) compared to both atoms and diatomic molecules. For example, all polyatomic molecules have long-lived states arising from nuclear motion with angular momentum about the internuclear axis. These states exhibit linear, Debye-level Stark shifts at very low applied electric fields and offer distinct Stark-shifted level structures that are absent in laser-coolable diatomic molecules. These and other features in polyatomic molecules can be applied to quantum simulation, fundamental symmetry tests, searches for dark matter, and particle physics beyond the Standard Model, potentially at the 1 PeV scale. Generic classes of polyatomic molecules have been identified as amenable to laser cooling into the ultracold (~1 μK) regime. One class is that of metal oxide radicals (MOR), which includes linear, symmetric top, and asymmetric top species. In this talk I will discuss some of the past experiments that brought us to this point, and the challenges and scientific opportunities with the laser cooling of polyatomic molecules. Results on SrOH, YbOH, CaOH and CaOCH3 will be discussed, as well as preliminary work on more complex species.