Quantum Control Limits Excitation Spread

Julius Bohm and colleagues at RPTU University demonstrate that a quantum contact process exhibits more complex behaviour and greater controllability than its classical analogue. The study reveals that excitation spreading on a topologically designed lattice can be precisely controlled, even confined to specific areas or activated in discrete increments using topological pumps. A key finding is the mapping of the complex dynamics of multiple interacting excitations to a simplified single-particle model, linking many-body behaviour to underlying topological properties. This provides a strong understanding of how quantum mechanics can enhance contact processes, common in classical systems ranging from disease spread to information networks.

Rydberg facilitation drives controlled excitation propagation in atomic lattices

A technique based on coherent Rydberg facilitation within a one-dimensional lattice of trapped atoms enabled the engineering of a quantum contact process. This chain reaction relies on quantum connections for energy transfer, differing from a purely classical domino effect. Laser fields coupled atoms between ground and Rydberg states, creating strong van-der-Waals interactions that enable energy transfer only when precisely one neighbouring atom is already excited.

Careful tuning of laser parameters and lattice spacing allowed researchers to map the complex many-body dynamics onto a simplified model, providing precise control over excitation spreading. Simulations, performed using time-evolving block decimation with a laser detuning of -500 relative to the Rabi frequency and an interaction potential plus detuning equal to zero, enabled resonant driving and the required excitation constraint. The approach provides a foundation for understanding complex interactions within the lattice, focusing on a model where excitation only occurs if one neighbouring atom is already excited, mirroring classical epidemic models.

Topological control of excitation spreading and on-demand energy localisation

Demonstrated is control over excitation spreading in a quantum contact process, achieving confinement to topologically protected subspaces with a precision previously impossible in classical systems. This surpasses earlier quantum methods by enabling confinement of excitation to either a single site or the entire lattice, a level of control absent in classical contact processes. The complex dynamics of multiple interacting excitations were mapped to a simplified single-particle model, revealing a link between many-body behaviour and underlying topological properties.

Topological pumps now control excitation spreading in quantized steps, a capability absent in traditional models of energy transfer. Excitation confinement, limiting energy flow to a single site or the entire lattice, occurs with remarkable precision, evidenced by observed oscillations between one site and the full lattice in simulations of a four-site system. This behaviour arises because the quantum contact process mirrors the Su-Schriefer-Heeger model, a system known for its topologically protected edge states that prevent energy leakage. A ‘topological Thouless pump’ also demonstrated control, periodically modulating energies and rates to direct excitation spreading. The experiments utilised a one-dimensional lattice of trapped atoms, with strong van-der-Waals interactions creating the necessary kinetic constraints for the quantum contact process, and modelling the dynamics with time-evolving block decimation.

Rydberg facilitation enables precise control of excitation propagation in a one-dimensional lattice

Controlling energy flow is important for advances in quantum technologies, with potential applications ranging from secure communication to novel sensing devices. A new level of precision in manipulating excitation spreading has been demonstrated, confining it to specific areas or propagating it across an entire system. However, the current implementation relies heavily on the specific conditions of Rydberg facilitation within a one-dimensional lattice.

Achieving the required large offset detuning raises questions about practical scalability. Precise control over excitation spreading within a lattice of trapped atoms has been demonstrated, mirroring processes seen in classical systems like disease propagation and information distribution. A quantum contact process on a topologically non-trivial lattice can be confined to a protected subspace, either a single site or a fully excited lattice. Furthermore, excitation spreading can occur in quantized steps when employing topological pumps.

The dynamics of excited domains map to an effective single-particle model, which also determines the topological properties of the system. This considers coherent Rydberg facilitation in a one-dimensional lattice of trapped atoms. Implementing a quantum contact process on a lattice with specific topological properties allows for the confinement or propagation of excitation, the movement of energy, with unprecedented accuracy. Energy flow can be controlled in discrete, measurable steps by utilising ‘topological pumps’, a capability absent in classical systems. This establishes a foundation for exploring how topological principles can engineer complex quantum phenomena, potentially leading to advancements in areas like quantum simulation and materials science.

Researchers demonstrated precise control over the spread of excitation in a one-dimensional lattice of trapped atoms. This quantum contact process allows for confinement of excitation to a single site or across the entire lattice, and propagation occurs in discrete, measurable steps using topological pumps. The many-body dynamics simplify to an effective single-particle model, revealing the link between topology and excitation behaviour. The authors suggest this work provides a basis for further exploration of topological principles in quantum systems.