Complex quantum systems maintain memory of their initial conditions during evolution. A one-dimensional chain of Rydberg atoms governed by a constrained four-body interaction exhibits non-ergodic dynamics, combining Rydberg blockade and antiblockade mechanisms. This enables revival of an initial atomic state, opening new avenues to explore exotic behaviour in quantum materials. Ultra-cold atoms display predictable quantum behaviour instead of randomness through this work.

This was achieved using chains of Rydberg atoms and carefully designed interactions between them; these interactions combine ‘blockade’, preventing excitation, and ‘antiblockade’, allowing it under specific conditions. Manipulating how pairs of atoms change states only when their neighbours are also in a particular condition revealed unusual dynamics where initial atomic arrangements reappear later in time. Unusual behaviour within a chain of ultra-cold atoms unlocks new insights into quantum materials according to the University of Nottingham team.

Their work centres on Rydberg atoms, extremely fragile, highly excited atoms used as building blocks in quantum experiments due to their strong interactions, and how they can be manipulated to exhibit predictable behaviours rather than randomness. Carefully designing interactions between these atoms, combining ‘blockade’ which prevents excitation with ‘antiblockade’, allows for observation of non-ergodic dynamics; imagine shaking a box containing only one marble, it won’t explore all available space within the box.

This resulted in initial atomic arrangements reappearing later in time, suggesting a form of memory within the system. The team are now exploring whether this controlled behaviour extends beyond simple chains and into more complex configurations that mimic exotic materials.

Engineered Rydberg interactions enable prolonged coherent dynamics in ultracold atom arrays

Scientists have shown that Rydberg atom chains, exhibiting strong interactions between ultra-cold atoms, can sustain non-ergodic dynamics with a revival rate exceeding previous limitations. Prior to work struggled to maintain coherence beyond short timescales due to rapid energy dissipation; however, these new experiments show sustained oscillations for over thirty seconds. The breakthrough stems from engineering a precise interaction between ‘Rydberg blockade’, which prevents atomic excitation, and ‘antiblockade’ allowing it under specific conditions, creating a constrained four-body interaction where only neighbouring pairs transition simultaneously if their neighbours remain grounded.

This careful control enables the extended coherent behaviour observed in this system. Analysis reveals quantum many-body scar eigenstates nearly equally spaced in energy and strongly overlapping with all atoms initially being in the ground state, deviating from predictions based solely on atomic kinetic energy alone.

These tilted scars maintain local memory within the chain, evidenced by sizable long-range correlations extending across twenty-four atom chains; unlike those originating from alternative initial states, these findings potentially inform future designs for more robust quantum technologies as they move beyond simple two-atom couplings. Such arrangements expand understanding of how collective dynamics are influenced and offer a pathway to explore complex interactions between multiple atoms simultaneously.

Rydberg atom chains reveal pathways towards sustained observation of non-ergodic many-body physics

Revival of initial states was successfully demonstrated within their Rydberg atom chain by University of Nottingham researchers, a clear sign of non-ergodic behaviour. However, the extent to which this effect endures under realistic conditions remains unclear because external disturbances or imperfections during experiments could easily disrupt these delicate quantum oscillations. Maintaining such fragile quantum behaviour over extended timescales presents a key challenge; nevertheless, this demonstration identifies a specific pathway using alternating bond lengths in Rydberg atoms to create and study non-ergodic dynamics driven by complex four-body interactions.

The team’s work establishes a route to predictable quantum behaviour via constrained interactions within strings of ultra-cold atoms exhibiting strong connections when excited by light. This resulting non-ergodic dynamic manifests as revival of the original configuration over time and is quantified by L/2−1. Observation of how initial conditions are preserved allows for insights into many-body physics beyond simple two-atom couplings, opening new avenues in this field.

Researchers demonstrated that Rydberg atom chains can exhibit a return to their starting state, indicating behaviour where energy does not spread throughout the system as expected. This preservation of the initial quantum state arises from interactions between four atoms constrained by alternating bond lengths which create both blockade and antiblockade effects.

The study analytically determined ground state energies scaling linearly with chain length L, alongside nearly equally spaced scar eigenstates overlapping strongly with the all-grounded basis state. These findings provide a method for exploring non-ergodic dynamics using complex atomic interactions and extend understanding beyond simpler two-atom systems.

👉 More information
🗞 Nonthermal Dynamics of a One-dimensional Rydberg-atom Chain with Constraint Four-body Interactions
✍️ Tianyi Yan and Weibin Li
🧠 ArXiv: https://arxiv.org/abs/2608.20233

More like this