Talks

Markovian Control of Lindblad Steady States

Adiabaticity in open quantum systems described by parameter-dependent Lindblad dynamics can be defined with respect to the instantaneous steady state (ISS). While counterdiabatic protocols using an adiabatic gauge potential (AGP) have been formulated, they are practically challenging due to non-Markovian rates and non-local time-dependent jump operators. We resolve this by characterizing the AGP’s gauge freedom through its action on the excited, decaying modes. Separating the motion of the ISS into purity-preserving and purity-changing parts, we fix the freedom by mapping the latter onto a transport problem on a Markov network. The resulting closed-form AGP is Markovian by construction, and recovers the unitary result when dissipation vanishes. Variational optimization of time-independent, local jump operators substantially enhances fidelity in the boundary-driven XX model as its Liouvillian gap closes. The gauge fixing and variational techniques formulated in this work serve as a basis for efficient, experimentally implementable control protocols for accelerated steady state preparation in interacting open systems.

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CondMat for Dummies: Do I have a superconductor, a metal or an insulator?

In this talk we will explore how you can apply a simple criterion, built from various limits of a current–current correlation function, to identify whether a system is a superconductor, a metal or an insulator. This method rests on gauge invariance alone, so no knowledge of the microscopic order parameter or pairing symmetry is required! As an example, we will apply it to the disordered attractive Hubbard model with determinant quantum Monte Carlo numerics, and hence track its superconductor to insulator transition.

Life at High Reynolds Number

Unlike coffee and cream that homogenize when stirred, growing micro-organisms (e.g., bacteria and unicellular marine organisms) can actively kill each other and avoid mixing. How do such antagonistic interactions impact the growth and survival of competing strains, while being spatially advected by turbulent flows? By using analytic arguments and numerical simulations of a continuum model, we describe the dynamics of two antagonistic strains that are dispersed by both compressible and incompressible turbulent flows in two spatial dimensions. A key parameter is the ratio of the fluid transport time to that of biological reproduction, which determines the winning organism that ultimately takes over the whole population from an initial heterogeneous state, a process known as fixation. By quantifying the probability and mean time for fixation, we discuss how turbulence raises the threshold for biological nucleation and antagonism suppresses flow-induced mixing by depleting the population at interfaces. We highlight the unusual biological consequences of the interplay of turbulent fluid flows with antagonistic population dynamics, with potential implications for marine microbial ecology and origins of biological chirality.

ATOM26 Colloquium

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Quantum Dynamics Seminar: tba