"Quantum optics using atom arrays"

Abstract:

Quantum atom-light interfaces enable access to a wealth of quantum phenomena and applications within quantum information science. Despite this, a frontier that remains elusive is the realization and exploration of strongly correlated phenomena, due to two complementary problems. On one hand, such systems still suffer from significant dissipation, particularly at the level of individual quanta. This is evidenced by the fact that state-of-the-art photon-photon gates still suffer an error probability of over 50%. On the other hand, there is a prevailing strategy to improve atom-light interaction efficiencies, by encoding processes into the collective response of many atoms. However, this strategy has the downside that collective spin or mean-field descriptions are typically good starting points to understand the physics, with paradigmatic examples being superradiance or spin squeezing. Such descriptions are incompatible with most known strongly correlated phenomena within physics.

Here, we discuss our efforts to devise novel paradigms to enable the exploration of strongly correlated physics using atoms and light. The starting point is the realization that the dominant dissipation mechanism for atom-light interfaces, spontaneous emission, is actually a correlated form of dissipation, due to the interference of light emitted by different atoms. The correlated nature becomes especially strong and controllable in dense atom arrays. We will first discuss how correlated emission can be harnessed to implement high-efficiency building blocks for quantum information processing, such as quantum memories and photon gates. We will then discuss our ongoing efforts to encode strongly correlated phenomena into "subradiant" manifolds where destructive interference strongly suppresses spontaneous emission. In particular, we focus on the exploration of topological quantum spin liquid phases using arrays of atoms coupled to a high-finesse cavity. These phases host a number of exotic properties, which include quasi-particle excitations with fractional or anyonic statistics, emergent gauge fields, and subtle long-range entanglement patterns.

Bio:

Darrick Chang has been a professor at ICFO and leader of the research group on Theoretical Quantum Nanophotonics there since 2011. Previously, he earned his bachelors and PhD degrees in physics from Stanford University and Harvard University, respectively, and was a prize postdoctoral fellow at the Institute of Quantum Information at Caltech. Among his recognitions, he has been awarded both the ERC Starting and Consolidator Grants.

Broadly, his research focuses on developing novel techniques to manipulate quantum interactions between light and matter, and advancing theoretical tools to understand these phenomena. The work covers both technological applications, such as for quantum information processing, and fundamental science such as the emergence of strongly correlated phenomena in light-matter interfaces. His research spans a wide multi-disciplinary scope, including quantum optics, atomic physics, nanophotonics, optomechanics, nonlinear optics, quantum information science, and 2D materials. His group also works closely with leading experimental groups worldwide, to bring their theoretical ideas toward reality.