Vedika Khemani wins McMillan Award and APS Valley Prize for work on time crystals

VEDIKA KHEMANI, an assistant professor of physics, was recognized twice last month for “seminal theoretical work” on novel non-equilibrium quantum phases of matter, most notably the discovery of the “Floquet time crystal” phase.

Vedika Khemani (Courtesy Vedika Khemani)

The American Physical Society’s George E. Valley Jr. Prize is given “to recognize one individual in the early stages of his or her career for an outstanding scientific contribution to physics that is deemed to have significant potential for a dramatic impact on the field,” according to the prize website. The award consists of a monetary prize, a certificate citing the contribution made by the recipient, an allowance for travel to the APS Medal and Prize Ceremony and Reception and an invited talk at an APS meeting.

The McMillan Award is presented annually to “to an outstanding young researcher in condensed matter physics” to recognize “exceptional achievements in theory, experiment, or both.” The prize is given in memory of the late William L. McMillan, who was a condensed matter physicist at the University of Illinois. The award consists of a monetary prize, a plaque and an invitation to present the annual McMillan Award Lecture at the University of Illinois.

“I’m very happy and grateful for this recognition. It’s very encouraging,” said Khemani, who is on the faculty in the School of Humanities and Sciences. “I’m fortunate to be part of a dynamic and supportive community of many wonderful collaborators and mentors.”

The emergence of a time crystal

Khemani is a theoretical physicist who studies many-body quantum systems, as opposed to studying the properties of a single atom or molecule. The field of condensed matter physics is concerned with the emergent properties – those that characterize the collection but not the individual constituents – of macroscopic quantum systems with large numbers of strongly interacting particles. The collective behavior of large quantum systems can lead to a diverse array of novel and exotic phases. The combination of many particles and strong interactions makes the study of such systems extremely challenging, and most theoretical work in this field considers systems within the context of equilibrium thermodynamics, a framework that affords many conceptual simplifications.

Khemani is being recognized for path-breaking work in developing theories of phase structure in many-body quantum systems out of equilibrium, leading to the discovery of an exotic, non-equilibrium phase of matter called a time crystal. A time crystal is a collection of many quantum particles whose state constantly changes in time, never reaching equilibrium. Just like the atoms of a regular crystal repeat in space, a time crystal repeats in time and pulses indefinitely without any outside energy being put into the system. While one or a few particles can easily show such time dependence, this behavior in a many-body system would break the first two Laws of Thermodynamics – which is why prior versions of this idea were roundly rejected as “perpetual motion machines.”

The work by Khemani and collaborators evaded these fundamental constraints by postulating a non-equilibrium time crystal variant, and their theory guided various experiments that have observed precursors of this phase.

“It’s a lot of fun doing what I do,” said Khemani, who is also a member of Q-FARM, Stanford’s broad interdisciplinary initiative in quantum science and engineering. “It’s exciting to be in this new research space where we’re making connections between so many research areas that have evolved quite separately until recently.”

Stanford Vice Provost and Dean of Research Kathryn Moler and physics Professor David Goldhaber-Gordon are previous recipients of the McMillan Award. Goldhaber-Gordon was also the inaugural winner of the APS Valley Prize.