I am a physicist specialising in the theory of quantum fluids in cold atoms and superconductors. Together with my collaborators, we are interested in discovering and understanding novel phenomena in far-from-equilibrium scenarios. We employ both analytical and numerical tools to model the dynamics of various many-body systems.
Research highlights are shown in the gallery below -- click the pictures for more information.
27 June 2022
Observation of a continuous time crystal
In our work published in Science chosen for "First Release", we demonstrate the first observation of a continuous time crystal in a lab. This time crystal is very close to the original time crystal proposed by Nobel laureate, Frank Wilczek, in his seminal work in 2012. A continuous time crystal is similar to a standard crystal, like ice, where we know that there is a periodic pattern in space but we can not pinpoint the exact location of the molecules. In a continuous time crystal, the time when the system starts to oscillate is random.
We specifically use a Bose-Einstein condensate inside an optical cavity to demonstrate that limit cycles, marked by oscillating photon occupation in the cavity, may emerge in the system under the right conditions. We showed that these limit cycles exhibit the robustness and spontaneous symmetry breaking expected of a continuous time crystal.
23 April 2022
Stable and Prethermal Dissipative Time Crystals
While the dissipative time crystal (DTC) that we have recently observed (Physical Review Letter) has been shown to be qualitatively consistent with a theoretical description in the ideal limit, the question remains if this new phase of matter can remain stable beyond the idealised scenario. In our work published in Physical Review A, we have investigated the stability of DTCs in the presence of an inhomogeneous trap and competing short- and long-range interactions, which push the system beyond the ideal case.
By mapping the phase diagram for various conditions, we show that the DTC can indeed remain stable and robust despite the presence of imperfections or mean-field breaking components. Moreover, we discover a new type of DTC, which we call prethermal dissipative time crystals. A prethermal DTC is characterised by increasing lifetime as the system is effectively driven faster. Our study demonstrates a general strategy to determine the influence of inevitable imperfections on any many-body state that is created in atom-cavity systems.
13 December 2021
Realisation of a three-level Dicke model
The Dicke model is one of the fundamental models in understanding the interaction between light and matter. The standard Dicke model involves two-level atoms interacting with a single quantum mode of light. In our joint publications appearing back-to-back in Physical Review A and Physical Review Letters, we have shown that a shaken atom-cavity system can emulate a driven three-level generalisation of the Dicke model.
We have theoretically predicted that the periodically driven three-level Dicke model has three dynamical signatures: (1) light-induced superradiance, (2) light-enhanced superradiance, and (3) incommensurate time crystalline phase. In our experiment, we have observed the emergence of an incommensurate time crytal, which also serves as a smoking gun for the quantum simulation of the three-level Dicke model.
23 July 2021
Observation of a dissipative time crystal
Together with collaborators from the University of Hamburg, we were able to create a time crystal that is exposed to the environment in a controlled way. Using a Bose-Einstein condensate inside an optical cavity, we demonstrate that periodic modulation of the light-mater coupling may lead to a periodic switching of the spatial configuration of the atoms between two sublattices of a chequerboard pattern. More interestingly, the complete cycle requires two driving periods suggesting that time-translation symmetry is broken - a hallmark of time crystals.
Our work represents a crucial step in potentially making this phase of matter useful since almost all time crystals require isolation from the environment. On a more fundamental level, we provide a prototypical example of interesting phases arising from the complex interplay between many-body interaction, driving, and dissipation.
10 June 2021
Higgs mode mediated enhancement of interlayer transport in high-Tc cuprate superconductors
The famous Higgs boson in particle physics has an analogue in condensed matter, which is aptly called the Higgs mode. Beyond fundamental and theoretical interests, can we possibly use this elusive mode for practical purposes?
In our recently published work, the answer appears to be "yes". In particular, we predict that the transport property of cuprate superconductors can be enhanced by essentially shining them with light at a frequency slightly above the Higgs frequency. The resulting oscillation of the Higgs mode then leads to a parametric amplification of the superconducting response.