arXiv subjects

Alan Tsidilkovski

Publications and source records attributed to Alan Tsidilkovski.

3 recordsLinked to original sources

arXiv2026

The Kubo-Thermalization Correspondence

Quantum thermalization describes how interacting quantum systems relax toward thermal equilibrium, a central problem in modern physics. Yet most experimental information on many-body systems comes from short-time transition spectroscopy, typically interpreted within Kubo's linear-response framework. These perspectives - long-time equilibration versus short-time response - seem fundamentally disconnected. Here we establish an exact link between them: the Kubo-Thermalization correspondence, which connects long-time thermalized magnetization under weak driving to short-time linear-response spectra for a spin coupled to a thermal bath. The correspondence holds even when the steady state differs substantially from the initial state and when each regime is individually difficult to describe theoretically. We experimentally confirm the correspondence using effective spin-1/2 impurities realized with ultracold fermions in two internal states coupled to a Fermi sea. Our results provide a rare exact statement about quantum thermalization and offer a novel route to infer thermalization dynamics from equilibrium response measurements in strongly interacting quantum systems, independent of microscopic details of the system-bath coupling.

cond-mat.quant-gas↗

arXiv2025

Emergence of Fermi's Golden Rule in the Probing of a Quantum Many-Body System

Fermi's Golden Rule (FGR) is one of the most impactful formulas in quantum mechanics, providing a link between easy-to-measure observables - such as transition rates - and fundamental microscopic properties - such as density of states or spectral functions. Its validity relies on three key assumptions: the existence of a continuum, an appropriate time window, and a weak coupling. Understanding the regime of validity of FGR is critical for the proper interpretation of most spectroscopic experiments. While the assumptions underlying FGR are straightforward to analyze in simple models, their applicability is significantly more complex in quantum many-body systems. Here, we observe the emergence and breakdown of FGR, using a strongly interacting homogeneous spin-$1/2$ Fermi gas coupled to a radio-frequency (rf) field. Measuring the transition probability into an outcoupled internal state, we map the system's dynamical response diagram versus the rf-pulse duration $t$ and Rabi frequency $\Omega_0$. For weak drives, we identify three regimes: an early-time regime where the transition probability takes off as $t^2$, an intermediate-time FGR regime, and a long-time non-perturbative regime. Beyond a threshold Rabi frequency, Rabi oscillations appear. Our results provide a blueprint for the applicability of linear response theory to the spectroscopy of quantum many-body systems.

cond-mat.quant-gas↗

arXiv2024

A compact and open-source microcontroller-based rapid auto-alignment system

Maintaining stable and precise alignment of a laser beam is crucial in many optical setups. In this work, we present a microcontroller-based rapid auto-alignment system that detects and corrects for drifts in a laser beam trajectory using a pair of two-dimensional duo-lateral position sensing detectors (PSDs) and a pair of mirror mounts with piezoelectric actuators. We develop hardware and software for interfacing with the PSDs and for controlling the motion of the piezoelectric mirrors mounts. Our auto-alignment strategy -- implemented as a state machine on the microcontroller by a FreeRTOS kernel -- is based on a simple linearized geometrical optical model. We benchmark our system using the standard case of coupling laser light efficiently into the guided mode of a single-mode fiber optic patch cable. We can recover the maximum fiber coupling efficiency in $\sim10$ seconds, even for a laser beam that was misaligned to the point of zero fiber coupling.

physics.ins-det↗