The (PXP) Model Demonstrates Long-Range Quantum Scars in Rydberg-Cavity Systems

Rydberg atoms coupled to optical cavities represent a rapidly developing platform for quantum simulation and information processing, offering a unique combination of long-range and short-range interactions. Hossein Hosseinabadi, Riccardo J. Valencia-Tortora, and Aleksandr N. Mikheev, working alongside colleagues from institutions including ICFO and the Max Planck Institutes, present a new theoretical model, termed (PXP), that captures the essential physics of these hybrid systems. This model reveals the existence of atypical quantum states, known as long-range quantum scars, which defy conventional expectations of thermalisation and exhibit remarkably slow entanglement growth. Unlike previously studied systems, these scars demonstrate logarithmic entanglement dynamics, offering a fundamentally different pathway for quantum information propagation and establishing a versatile framework for exploring the potential of Rydberg-cavity quantum systems.

Quantum Scars Persist in Open Quantum Systems

The (PXP)2 model, known for its unusual quantum properties, exhibits long-range quantum scars within optical cavities. Researchers investigated how these scars, atypical quantum states resisting typical thermal decay, emerge when combined with the principles of optical cavity quantum electrodynamics. By mapping the (PXP)2 model onto the modes of an optical cavity, the team created a hybrid quantum system to explore how quantum scars behave in an open environment where energy can dissipate. The results demonstrate that cavity-mediated interactions preserve the scar structure, leading to robust, long-lived quantum states even as energy is lost from the system.

Specifically, the scars exhibit a characteristic spatial profile and energy spectrum, remaining distinct from the surrounding thermal background. This work establishes a platform for studying the interplay between many-body localisation, quantum scars, and dissipation, potentially enabling the development of robust quantum memories and information processing schemes. The research highlights the potential of utilising quantum scars to protect quantum information from environmental noise and decoherence.

Rydberg and cavity systems are emerging platforms for quantum simulation and quantum information processing. These hybrid architectures combine cavity photons, which mediate collective long-range couplings, and Rydberg excitations, which generate strong short-range interactions. Together, these mechanisms offer a versatile toolkit for manipulating and controlling quantum systems with high precision, allowing scientists to engineer tailored quantum systems with specific properties and functionalities essential for both fundamental research and practical applications.

Rydberg Arrays Simulate Quantum Phase Transitions

This collection of research papers covers a broad range of topics in quantum physics and condensed matter physics, with a focus on quantum simulation using Rydberg atom arrays and optical cavities. The papers explore diverse areas, including the creation and control of Rydberg atoms, the study of quantum phase transitions, and the behaviour of many-body quantum systems. A central theme is the importance of long-range interactions in these systems, which fundamentally alter their behaviour compared to those with short-range interactions. The research explores concepts such as prethermalization, where systems appear to reach a quasi-equilibrium before eventually thermalizing, and the growth and spreading of entanglement in quantum systems. The use of optical cavities to enhance light-matter interactions and create strong coupling between atoms and photons is a key aspect of many of the studies. The collection demonstrates a growing interest in understanding and controlling complex quantum phenomena using these advanced experimental and theoretical techniques.

The papers can be broadly categorized by their focus. Some papers detail the fundamental creation and control of Rydberg atom arrays, establishing the platform for quantum simulation. Others focus on simulating specific model systems and exploring quantum phase transitions. A significant portion investigates the dynamics of many-body systems, including entanglement growth and prethermalization. Several papers address the role of dissipation and open quantum systems.

The research demonstrates a strong connection between Rydberg atom arrays and cavity quantum electrodynamics. The Rydberg atom arrays provide the physical platform, while the optical cavities enhance light-matter interactions and enable stronger control. The studies of prethermalization and many-body dynamics build upon these foundations, exploring the complex behaviour of quantum systems.

Rydberg Systems Exhibit Novel Superradiant Phase

This research establishes a minimal theoretical framework for understanding Rydberg-cavity systems, platforms that combine the benefits of both cavity quantum electrodynamics and strong Rydberg atom interactions. Scientists developed a model capturing the interplay between long-range interactions mediated by cavity photons and short-range interactions arising from Rydberg excitations, focusing on the strong interaction regime. This approach yields a kinetically constrained model allowing for detailed analysis of system behaviour. Investigations into the equilibrium phases reveal three distinct states: a paramagnetic phase, a Néel-ordered phase, and a blockaded ferromagnetic/superradiant phase.

Notably, the superradiant phase exhibits characteristics not found in conventional systems, displaying robustness against quantum fluctuations and exceeding classical magnetization limits due to the Rydberg blockade. Furthermore, the team identified long-range quantum many-body scars in the system’s out-of-equilibrium dynamics, demonstrating atypical behaviour where entanglement grows logarithmically with time, a contrast to the linear growth observed in short-range systems. The authors acknowledge that their model represents a simplification of real experimental setups, focusing on one-dimensional systems and neglecting certain complexities of atomic arrangements. Future research directions include extending the model to higher dimensions and exploring the impact of disorder on the observed phenomena. This work provides a crucial stepping stone for both theoretical and experimental investigations into Rydberg-cavity systems and their potential for realizing novel quantum many-body physics.