Quantum Particles Now Move with Energy from Their Surroundings

Jeanne Gipouloux and colleagues at the École normale supérieure, PSL, investigate the creation of active quantum particles driven by engineered dissipation, a process where energy loss from a coupled environment fuels particle movement. Several distinct models, including quantum versions of established active behaviour such as run-and-tumble dynamics, exhibit characteristics of active motion. The work reveals a transition from standard diffusion to active-diffusive behaviour over time, quantified by an effective Péclet number of 2, and highlights a notable sensitivity to system boundaries arising from the Liouville skin effect. These findings offer key insights into quantum active matter and suggest potential experimental implementations using superconducting circuits or cold gases, enabling the exploration of many-body effects in these systems. Engineered dissipation drives directed motion and heightened Péclet numbers in quantum systems The effective Péclet number, a dimensionless quantity representing the ratio of advective to diffusive transport, increased from values near one to exceeding ten in these quantum systems. This dramatic shift signifies a transition from behaviour dominated by random diffusion, where particle displacement is governed by random fluctuations, to one governed by directed, active motion. Traditionally, maintaining directed movement in quantum particles necessitated constant external forcing, such as the application of a continuous electromagnetic field. This external intervention introduces complexities and limitations in controlling the system. Gilles Gipouloux and colleagues at the École normale supérieure, PSL, demonstrated this enhanced activity across diverse models, including quantum analogues of run-and-tumble dynamics and active Brownian motion. The significance of exceeding a Péclet number of 10 lies in the clear dominance of advective transport; the particle’s directed motion overwhelms the randomising effect of diffusion, indicating a robust self-propelling capability. All of this was driven by engineered dissipation, a process where energy loss from a coupled environment fuels particle movement. Unlike passive dissipation, which simply dampens motion, engineered dissipation is carefully designed to impart a directional bias. This is achieved by coupling the quantum particle to a non-equilibrium environment, such as a reservoir with a controlled chemical potential gradient or a driven-dissipative bath. A strong sensitivity to system boundaries stems from the Liouville skin effect, a phenomenon where quantum states accumulate at the edges of a non-Hermitian system. This accumulation arises because the engineered dissipation breaks the Hermiticity of the Hamiltonian, leading to an asymmetry in the particle’s dynamics. The Liouville skin effect is particularly relevant in open quantum systems and can significantly alter the observed behaviour, necessitating careful consideration in experimental design. A particle moving on a lattice further validated these findings, incorporating both coherent and dissipative hopping. Coherent hopping describes the quantum mechanical evolution of the particle between lattice sites, while dissipative hopping represents the energy loss associated with transitions. Despite differing microscopic mechanisms, the model replicated the transition to active behaviour, exhibiting a crossover from diffusive to active-diffusive behaviour over time. The lattice model allows for a more intuitive understanding of how local dissipation can give rise to global directed motion. This transition to active behaviour is a key indicator of self-propelled motion, analogous to the behaviour of biological organisms like bacteria or active colloids. The quantification of this behaviour via the Péclet number provides a rigorous metric for assessing the degree of activity. Further investigation is needed to determine how these results translate to more complex scenarios, as current simulations focus on single particles in idealised conditions. Specifically, the influence of particle density, inter-particle interactions, and environmental noise needs to be explored. Scaling to many-body systems or accounting for realistic experimental imperfections, such as imperfections in the fabrication of superconducting circuits or fluctuations in laser intensity for cold gas experiments, remains a significant challenge. Addressing these challenges is crucial for bridging the gap between theoretical predictions and experimental realisation. Collective quantum motion necessitates extending single-particle dissipation models Engineered dissipation offers a compelling new pathway to induce movement in quantum particles, circumventing the need for continuous external forcing typically required to sustain directed motion. This approach opens up possibilities for creating self-propelled quantum devices and exploring novel quantum phenomena. Current models, however, treat particles in isolation, a simplification that may not hold when considering many interacting quantum bodies. In a many-body system, the dissipation experienced by one particle can be influenced by the presence and motion of other particles, leading to complex collective behaviours. Understanding how collective behaviour emerges from these individual active units remains an open question, presenting a formidable theoretical hurdle for scaling these findings to realistically complex systems where particle interactions are significant. Developing theoretical frameworks that accurately capture these interactions is essential for predicting and controlling the behaviour of quantum active matter. Consistent active behaviour across diverse theoretical frameworks solidifies the underlying principle of dissipation-driven quantum motion, establishing a vital foundation for exploring more complex, realistic scenarios. The robustness of this principle suggests that it is not merely an artefact of a specific model but rather a fundamental consequence of coupling quantum systems to engineered dissipative environments. It provides a set of tools to begin untangling how many quantum bodies might collectively exhibit active behaviour, which is vital for future developments in quantum technologies and materials science. For example, understanding collective active behaviour could lead to the development of novel quantum sensors, actuators, or even self-assembling quantum materials. An increase in the effective Péclet number, signifying directed motion, characterised the successful demonstration of a transition from standard diffusion to active-diffusive behaviour across diverse quantum models. These models include those mirroring active Brownian motion, a classical model widely used to describe the motion of active particles. The observed sensitivity to system boundaries, where quantum states accumulate at edges, highlights a crucial consideration for future experimental designs. Mitigating the effects of the Liouville skin effect may require careful engineering of the system geometry or the use of boundary conditions that minimise state accumulation. The research demonstrated consistent active behaviour across several quantum models, all driven by engineered dissipation. This matters because it suggests a universal principle governing the motion of quantum particles in non-equilibrium environments, moving beyond model-specific results. Observing a transition to active-diffusive behaviour, characterised by an increased Péclet number, and acknowledging boundary effects like the Liouville skin effect, provides crucial insights for future experimental designs utilising superconducting circuits or cold gases. This work lays the groundwork for investigating how many interacting quantum particles might exhibit collective active behaviour, potentially leading to advancements in quantum technologies and materials. 👉 More information🗞 Active Quantum Particles from Engineered Dissipation🧠 ArXiv: https://arxiv.org/abs/2603.19094 Tags: