Stark Manifold Dynamics with Rydberg Atoms Advances Understanding of Thermalization

The tendency of isolated systems to reach a stable, predictable state, known as thermalization, remains a fundamental question in physics, with the eigenstate thermalization hypothesis offering one potential explanation. Sarah E. Spielman, Sage M. Thomas, and Maja Teofilovska, alongside colleagues from Bryn Mawr College and Ursinus College, investigate this phenomenon using ultracold rubidium atoms. The team predicts the expected thermal state of these atoms as they exchange energy through long-range interactions and then compares this prediction to the actual behaviour of the atoms held in a magnetic trap. Their findings reveal that, contrary to expectations, the atoms do not consistently thermalize, although they do approach the predicted thermal state at higher densities, offering new insights into the conditions required for achieving equilibrium in isolated quantum systems.

Rydberg Atoms and Quantum Thermalization Prediction

The researchers use dynamical typicality to predict the thermal state of ultra-cold Rydberg atoms interacting within a Stark manifold, investigating how interactions drive a system towards thermal equilibrium. They explore the conditions under which an isolated quantum system behaves as if in thermal equilibrium with a larger environment, examining the evolution of initial states to determine when behaviour aligns with a thermal distribution and testing the eigenstate thermalization hypothesis in a controlled setting. The researchers observed both thermalization and fragmentation of the quantum state space, with fragmentation hindering thermalization, and identified Z2k scars, a type of quantum many-body scar protecting states from decay. Thermalization appears restricted to fragmented regions of the state space, meaning the system does not explore the entire state space as expected in full thermalization, and time-resolved observations tracked this evolution. The work contributes to understanding non-ergodic behaviour in quantum systems, where the system cannot explore all accessible states, and provides insight into how quantum scars protect states from decay.

This research has implications for quantum information processing, as controlling and protecting quantum states is crucial for building quantum computers, bridging theory and experiment by providing data for testing models of quantum thermalization and many-body scars. The observation of Hilbert space fragmentation, where the system breaks into disconnected regions, adds to evidence that it significantly impacts quantum dynamics. This research demonstrates a complex interplay between thermalization, fragmentation, and quantum scars in a controlled Rydberg atom system, highlighting challenges in achieving thermal equilibrium and providing insights into non-ergodic behaviour. The findings align with previous work on thermalization in superconducting qubits, Hilbert space fragmentation in dipolar systems, and quantum scars in Rydberg atom chains, and relate to studies on prethermalization and many-body localization.

Thermalization Fails in Dipole-Dipole Systems

Researchers investigated the thermalization of isolated ultracold rubidium atoms interacting through long-range dipole-dipole forces, monitoring their evolution after preparing them in a specific energy configuration and comparing the resulting state to predictions from the eigenstate thermalization hypothesis. Their experiments reveal that while the atoms approach a thermal state at higher densities, they generally do not fully thermalize, retaining excess population in the initial energy cluster, challenging the expectation of complete thermalization in isolated quantum systems. The data suggest quantum many-body scars, states resisting thermalization, may be responsible for this behaviour, given the system’s interaction dynamics. The authors acknowledge that incomplete thermalization may be linked to the experiment’s initial conditions and specific energy levels, with future work focusing on refining excitation techniques and exploring behaviour with different initial states to further investigate the role of quantum scars and edge effects in the thermalization process.