# Qi Zhou

## Quantum Gases Group

## Department of Physics and Astronomy

## Purdue University

### A pen,

### A few pieces of paper,

### A computer,

### A cup of tea or coffee,

### A theorist works like this.

### We study a wide range of topics in quantum gases and related fields, such as synthetic gauge fields for ultracold atoms, strongly interacting bosons and fermions, quantum many-body dynamics, and connections between few-body and many-body physics, among many others.

## Research Highlights

### Quantum coherence in photoassociation

Though it is in general believed that photoassociation leads to two-body loss, our collaborators, Prof. Yong Chen's group, and we have found that a coherent superposition of internal states of atoms (colored spheres) gives rise to a complete suppression of this type of two-body loss, due to a destructive interference of two photoassociation pathways (PRL, 2018). This is a concrete example of quantum control of photochemical reaction.

### "More is different" in topological defects

A single boson with four internal or external states (colored spheres) sees a Yang monopole of charge 1 in a five-dimensional parameter space. What will a collection of interacting bosons see ? We show that they see something very different, including multiple Yang monopoles scattered in the parameter space or a giant Yang monopole, whose charge is the total particle number squared. More interestingly, many bosons together may even see continuous topological defects (PRL, 2018).

### Review article on Synthetic Gauge Fields

Recent years have seen fascinating progress in the study of synthetic gauge fields for charge-neutral ultracold atoms. This topical review (Journal of Physics B, 2017) surveys recent developments in using synthetic gauge fields to manipulate novel quantum phenomena that are not easy to access in other systems, ranging from unconventional single-particle dispersions to novel quantum many-body states induced by the interplay between interactions and synthetic gauge fields.

### Two-dimensional synthetic gauge fields in K40

Spinâ€“orbit coupling (SOC) is central to many physical phenomena. Whereas laserâ€“atom interaction provides physicists a unique means to create synthetic SOC in ultracold atoms, a two-dimensional (2D) synthetic SOC eluded experiments for quite a while. In this work (Nature Physics, 2016), a 2D synthetic SOC was created for the first time in a laboratory by our experimental collaborators, Prof. Jing Zhang's group at Shanxi University.

### Contact matrix and many-body correlations

In ultracold atoms, the average inter-particle spacing is much larger than the range of interactions. Such separation of length scales allows us to define contact matrix, which governs not only universal thermodynamic relations of dilute systems, but also correlations in many-body systems, for instance, atomic quantum Hall states (Physical Review Letters, 2016) and some intriguing superfluids (Physical Review A, 2017).

### Chiral d-wave superfluid in shaken lattices

It is notably difficult to realize a chiral d-wave superfluid, a preliminary example of interacting topological superfluid, as a strong d-wave interaction is often required. This work (Physical Review Letters, 2015) presents a new principle for creating a chiral d-wave superfluid using a periodically driven lattice. Because of an imprinted 2D pseudospin-orbit coupling, s-wave interaction naturally creates a synthetic d-wave interaction and a chiral d-wave superfluid.

### Liftshitz point and non-condensed bosons

Half particles in the universe have a natural instinct to condense at zero temperature. We show that this textbook result will be changed by unconventional single-particle dispersions created by synthetic gauge fields (Nature communications, 2015). When quartic dispersions show up at the Lifshitz point, 2D algebraic quantum liquid rises at the ground state. A similar phenomena occurs in 1D when a non-Luttinger liquid emerges at the Lifshitz point (Physical Review A, Rapid Communication, 2014).

### When universality meets universality

Physical systems near a critical point are entirely governed by the universality class of the phase transitions. Dilute systems are governed by universal relations through contacts. Whereas these two types of universality describe distinct phenomena, this work (Nature Communications, 2014) establishes an intrinsic connection between them by revealing critical behaviors of the s-wave contact near continuous phase transition points.