Hybrid ion-atom systems combine the benefits of a single, well-controlled ion with those of a many-body quantum gas, offering prospects for quantum simulation, ultracold chemistry, and charged impurity physics [1, 2]. For the latter, the longer range of the atom-ion interaction, compared to that between two neutrals, is expected to give rise to interesting behaviour, for example the formation...
Theoretical study of nonequilibrium quantum thermodynamics in many-body interacting systems is typically restricted by the complexity of dynamical simulation. Integrable systems, despite their exact solutions, are often no exception to this. However, the recently developed theory of generalized hydrodynamics (GHD) is capable of capturing the large-scale dynamics of integrable and...
Active matter is a new kind of soft matter relevant to describe numerous biological problems with manifold realizations in two dimensions. I will discuss several intriguing aspects of its phase behavior including the melting of an active solide (with special emphasis on the role of dislocations and disclinations) and the mechanisms leading to motility induced phase separation.
In a one-dimensional lattice anyons can be defined via generalized commutation
relations containing a statistical parameter, which interpolates between the boson
limit and the pseudo-fermion limit. The corresponding anyon-Hubbard model is
mapped to a Bose-Hubbard model via a fractional Jordan-Wigner transformation,
yielding a complex hopping term with a density-dependent Peierls phase....
We develop the moment method for Bose-Einstein condensates at finite temperatures that enable us to study collective sound modes from the hydrodynamic to the collisionless regime [1]. In particular, we investigate collective excitations in a weakly interacting dilute Bose gas by applying the moment method to the Zaremba-Nikuni-Griffin equation, which is the coupled equation of the Boltzmann...
When a superfluid flows about a cylindrical obstacle, vortex-pairs are shed by the obstacle when the critical velocity is exceeded. This phenomenon was characterised in a theoretical study using the Gross-Pitaevskii equation by Frisch et al. (1992)[1]. They investigated this behaviour for an infinite obstacle (zero density inside) and found that above the critical velocity, vortex-pairs would...
In this work we present our investigations on Rabi coupled Fermi gases. Specifically, the behavior of a mobile spin-1/2 impurity atom immersed in a Fermi gas, where the interacting spin-↑ and non-interacting spin-↓ states of the impurity are Rabi coupled via an external field. This scenario resembles the classic problem of a two-state system interacting with a dissipative environment but with...
Despite the fundamentally different dissipation mechanisms, many laws and phenomena of classical turbulence equivalently manifest in quantum turbulence. The Reynolds law of dynamical similarity states that two objects of same geometry across different length scales are hydrodynamically equivalent under the same Reynolds number, leading to a universal drag coefficient law. We confirm the...
We have developed a microscopic many-body theory for two-dimensional coherent spectroscopy (2DCS) of polarons in one-dimensional (1D) materials [1]. Our theory incorporates contributions from three processes: excited-state emission (ESE), ground-state bleaching (GSB), and excited-state absorption (ESA). While ESE and GSB contributions can be accurately described using Chevy's ansatz with one...
Exciton-polariton condensates are non-equilibrium quantum fluids formed by short-lived hybrid light-matter particles in a semiconductor microcavity. In the steady-state regime, these particles decay via photon emission that inherits the coherence properties of the condensate. This so-called exciton-polariton laser is a promising source of coherent light for low-energy applications due to its...
The polaron, a particle dressed by excitations of a quantum medium, has been extensively studied in ultracold atomic gases. It represents the ultimate limit of imbalanced populations in quantum mixtures, and as such has relevance to the phase diagram of a wide range of systems, such as Fermi-Fermi, Bose-Bose, and Bose-Fermi gases. Here, I will present a variational approach to quantum mixtures...
Quantized vortices are central to two-dimensional superfluidity and quantum turbulence. Though there is great interest in observing and understanding their behaviour, vortices in superfluid helium-4 are particularly challenging due to their Angstrom-sized cores and low refractive indices. I will present my work in the experimental exploration of vortex dynamics in thin films of superfluid...
The quantum kicked rotor (QKR) is an archetypal system in the study of quantum chaos, and can be realised by periodically delta-kicking a cloud of ultracold atoms. This system is mathematically equivalent to a tight-binding model - up to an exchange of position and momentum space - and therefore exhibits behaviour analogous to electrons evolving in a lattice. Early work focused on "dynamical...
In this talk, we experimentally consider the problem of decaying turbulence in a Bose-Einstein condensate (BEC) superfluid. We begin with a shear layer comprised of quantum vortices formed between a stationary BEC and a stirred-in persistent current. This structure breaks down rapidly (<150 ms) through vortex pairing which we characterise through simple crystal structure analysis [1,2]....
The relationship regarding vortices and superfluidity in liquid helium originally proposed in the 1950s by Onsager and Feynman has been well established. Understanding vortices in 2D superfluids and their interactions can develop our understanding of quantum turbulence, quantum dissipation, and BKT phase transitions [1]. Despite this, observing these vortices is very difficult, due to the...
General relativity predicts that the curvature of spacetime induces spin rotations on a parallel transported particle. We deploy Unruh's analogue gravity picture and consider a quantised vortex embedded in a two-dimensional superfluid Bose-Einstein condensate. We show that such a vortex behaves dynamically like a charged particle with a spin in a gravitational field in a 2+1 dimensional...
