Researchers Find Dissipation Boosts Quantum Chaos

A new understanding of how information spreads within complex quantum systems enables improved predictions about their behaviour. Working with the Yukawa-Sachdev-Ye-Kitaev (YSYK) model, dissipation surprisingly enhances ‘scrambling’, which describes the rapid dispersal of quantum information throughout the system. This finding challenges previous expectations suggesting environmental interactions typically hinder this process; specifically for interactions involving more than two particles, scrambling increases alongside growing dissipation rates.

The work reveals how increasing environmental interactions can unexpectedly boost information dispersal within specific quantum systems, contrasting with expectations that such interactions usually impede it. Investigation of a complex system, the Yukawa-Sachdev-Ye-Kitaev (YSYK) model, discovered that ‘dissipation’, or energy loss to the surroundings, surprisingly enhances ‘scrambling’. Scrambling describes how quickly quantum information spreads through a material and is key for understanding chaotic behaviour in these systems.

Researchers from Princeton University and Université PSL have demonstrated that dissipation can enhance scrambling under specific conditions. This challenges conventional wisdom which typically assumes environmental interactions impede this process; previously it was thought coupling to an environment would suppress operator growth and exponential scrambling altogether.

To understand this finding, consider a Lindblad master equation, a mathematical framework describing evolving open quantum systems analogous to modelling the cooling rate of a hot cup of tea as heat escapes into its surroundings. The team investigated the Yukawa-Sachdev-Ye-Kitaev (YSYK) model, a disordered system utilising Majorana fermions, fundamental particles similar to electrons with unique properties potentially useful in strong quantum computing, and discovered that increasing energy loss to the surrounding environment can boost information dispersal for certain particle interaction strengths.

Enhanced quantum scrambling persists with increasing dissipation above pairwise interactions

The Lyapunov exponent, measuring scrambling rate within the Yukawa-Sachdev-Ye-Kitaev model, increased from below zero in prior work and remained positive for all dissipation strengths. Previously it was believed operator growth would be curtailed by environmental coupling; this represents a sharp departure from that expectation as it demonstrates quantum information dispersal is not invariably suppressed. The researchers demonstrated this enhancement specifically occurs when particle interactions exceed two (p > 2), revealing an unexpected durability of scrambling dynamics against energy loss at rates κ, something not observed before.

With interaction strengths exceeding two (p > 2), the rate of quantum scrambling, measured by the Lyapunov exponent, not only persisted despite energy loss but increased with dissipation rates κ. This behaviour occurred particularly when the ratio between bosons and fermions exceeded approximately 2/p². An anomalous relaxation regime was also revealed, where fermionic decay initially accelerates before being suppressed as leakage increases; this demonstrates complex interplay between coherent interactions and environmental coupling.

The case of p=2 presented unique characteristics, lying between fully chaotic regimes and integrable systems. Scientists continue pushing boundaries in quantum simulation seeking ways to build robust systems capable of tackling complex physical problems.

Although these calculations rely on approximations valid only when considering many interacting particles, a simplification of real quantum systems, the findings remain important because they reveal an unexpected role for dissipation. Identifying a critical boson-to-fermion ratio, ≈ 2/p^2, delineates differing dynamical behaviours within these systems, offering insight beyond traditional understandings of open quantum dynamics. This finding challenges expectations because dissipation typically suppresses such scrambling behaviour; however, it was observed to increase with higher rates κ for particle interactions exceeding two (p > 2).

Researchers identified a critical boson-to-fermion ratio around 2/p², which separates different ways the system behaves dynamically. The study provides insights into complex interactions within open quantum systems and how they might be simulated.