Unless otherwise specified, all talks are held starting at 1.15pm in the Theory Library on the 4th floor of Physics East.

Everyone is encouraged to ask questions during the talk. You are welcome to leave when you need to, otherwise the talk will usually wrap up by 2.30pm, at which point there will be biscuits.

Thursday 25th July 2024: Bryce Gadway (Penn State)

NB unusual time of 11am!

Synthetic dimensions in Rydberg atom arrays

Arrays of dipolar-interacting spins – magnetic atoms, polar molecules, and Rydberg atoms – represent powerful and versatile platforms for analog quantum simulation experiments. The internal state dynamics in such dipolar arrays provide a natural setting to explore problems of equilibrium and non-equilibrium quantum magnetism. The presence of many different internal states of the atoms and molecules in such experiments enables studies of large-spin magnetism, but also holds promise for more general quantum simulation studies. Here we describe how the simple addition of multi-frequency microwave fields to Rydberg arrays enables highly controllable studies of few- and many-body dynamics along an internal-state “synthetic” dimension. I’ll discuss several early studies in the Rydberg synthetic dimension platform, touching on interaction-driven phenomena relevant to topology, artificial gauge fields, and disorder-induced localization. Looking forward, such microwave manipulation opens up several new directions for exploring complex, driven quantum matter in dipolar arrays.

Thursday 25th April 2024: Martin Speight (University of Leeds)

Soliton crystals

Topological solitons are smooth spatially localized lump-like solutions of nonlinear field theories that can move around and interact in a particle-like manner. Examples are superconducting vortices, magnetic monopoles, domain walls and skyrmions. In condensed matter contexts they are usually observed in the laboratory in the form of spatially periodic arrays, analogous to crystals. The Abrikosov vortex lattice in type II superconductors is a prominent and influential example. Theoretical studies of soliton crystals almost always impose some plausible period lattice geometry (cubic, square or triangular) a priori, and optimize only over the size of the unit cell. I will argue that this assumption is, in general, ill-founded and that one should really optimize the system over the space of fields _and_ period lattices. The latter variation has an elegant reformulation in terms of the stress tensor of the field theory. When implemented numerically, one finds that much more exotic period lattices are possible than those conventionally imposed. The ideas will be illustrated by concentrating on skyrmion crystals in 2 and 3 spatial dimensions.

Joint work with Derek Harland and Paul Leask (also at Leeds).

Thursday 2nd May 2024: Alexander Mietke (University of Oxford)

How constraints and chirality guide self-organisation in living systems

Living matter has the fascinating ability to autonomously organise itself in space and time. Self-organisation refers typically to the fact that local interactions among microscopic agents enable an emerging dynamic that is seemingly coordinated on macroscopic length scales much larger than the agents. Classical examples are the interactions of actin and actin-binding molecules within the eukaryotic cell cortex, of cells within tissues or of entire organisms interacting within populations. While details of each self-organisation phenomenon will depend on the concrete biological system, mechanistic insights can still be developed by identifying generic features that are shared among systems – an abstraction that physics approaches provide many useful tools for. Two such generic features this talk focuses on are mechanical constraints and broken chiral symmetry, which are both ubiquitous in biological systems. Specifically, we will discuss the impact of mechanical constraints in guiding tissue morphogenesis in the flour beetle, the role of chirality in guiding the emergent properties of living crystals made of starfish embryos, as well as a mechanism to robustly establish a left-right body axis during nematode development when both, mechanical constraints and chirality, act in concert.

Thursday 9th May 2024: Orazio Scarlatella (University of Cambridge)

Strongly-coupled atomic arrays: a dynamical mean-field theory study

Subwavelength arrays of quantum emitters have emerged as an interesting platform displaying prominent collective effects. In this talk I will discuss the steady-states of such arrays under coherent driving, realizing an open quantum many-body problem with long range interactions and dissipation. I will discuss a Dynamical Mean Field Theory approach to the problem, for which few theoretical methods are available. I will show that the combination of dipolar interactions and regular geometry have a dramatic effect on the spectrum of emitted light in the strong-drive regime: the famous Mollow triplet characterizing the emission of a single atom develops a structured broadening with flat sidebands, distinguishing the emission of atomic arrays from that of disordered atomic clouds or of non-interacting emitters. For moderate drive strengths instead, I will show that the steady-state is influenced by the existence of guided modes in the single-particle regime that are completely decoupled from dissipation.