Showing 1–5 of 5 results for author: Brady, D

Dephasing in Rydberg Facilitation Due to State-Dependent Dipole Forces

Authors: Tom Schlegel, Evangelia Konstantinidou, Michael Fleischhauer, Daniel Brady

Abstract: Rydberg atoms allow for the experimental study of open many-body systems and nonequilibrium phenomena. High dephasing rates are a generic feature of these systems, and therefore they can often be described by rate equations, i.e. in the classical limit. In this work, we analyze one potential origin of the decoherence in Rydberg atoms: dipole-force induced dephasing. As the wave function of the Ryd… ▽ More Rydberg atoms allow for the experimental study of open many-body systems and nonequilibrium phenomena. High dephasing rates are a generic feature of these systems, and therefore they can often be described by rate equations, i.e. in the classical limit. In this work, we analyze one potential origin of the decoherence in Rydberg atoms: dipole-force induced dephasing. As the wave function of the Rydberg (spin-up) state is repelled in the presence of another nearby Rydberg atom, while the ground (spin-down) state diffuses in place, the Franck-Condon overlap between the two spin components quickly decays causing a decoherence of the spin transition. With an analytic approach we obtain a simple expression for the dephasing rate of the Rydberg state depending on atomic and laser parameters, which agrees with numerical findings. △ Less

Submitted 14 May, 2025; originally announced May 2025.

Quantum-Noise Induced Localization and Motional Squeezing in a Rydberg Quantum Simulator

Authors: Benno Bock, Daniel Brady, Michael Fleischhauer

Abstract: We investigate the interplay between mechanical forces and the internal-state dynamics of Rydberg excitations in atom-tweezer arrays. Dipole interactions between Rydberg atoms facilitate excitation spreading, but at the same time couple electronic (spin) degrees of freedom with motional (phonon) states. With increasing spin-phonon coupling, the growth dynamics of a cluster of excited Rydberg atoms… ▽ More We investigate the interplay between mechanical forces and the internal-state dynamics of Rydberg excitations in atom-tweezer arrays. Dipole interactions between Rydberg atoms facilitate excitation spreading, but at the same time couple electronic (spin) degrees of freedom with motional (phonon) states. With increasing spin-phonon coupling, the growth dynamics of a cluster of excited Rydberg atoms changes from ballistic spreading to Bloch-like oscillations and eventually to Anderson-like localization. We show that these effects are caused by quantum fluctuations in the phonon field: The dynamics of a Rydberg cluster can be mapped to a single particle in a semi-infinite lattice subject to phonon-induced energy shifts. The mean-field contribution of this energy shift leads to a linear potential gradient, resulting into Bloch-like oscillations. In addition, quantum fluctuations of phonons create a random local potential causing a transition from a regime of Bloch oscillations to localization. The spin-phonon coupling leads furthermore to highly correlated and non-classical phonon states in the form of squeezed states of the position of the Rydberg atoms. Depending on the form of the dipolar interaction potential, either in- or out-of-phase correlated oscillations of atoms emerge. △ Less

Submitted 24 August, 2026; v1 submitted 28 April, 2025; originally announced April 2025.

Comments: The first two authors contributed equally. Changes: modified title and author list; substantially extended content with different focus; now including observation and theoretical explanation of localization of excitation spreading

Anomalous Directed Percolation on a Dynamic Network using Rydberg Facilitation

Authors: Daniel Brady, Simon Ohler, Johannes Otterbach, Michael Fleischhauer

Abstract: The facilitation of Rydberg excitations in a gas of atoms provides an ideal model system to study epidemic evolution on (dynamic) networks and self organization of complex systems to the critical point of a non-equilibrium phase transition. Using Monte-Carlo simulations and a machine learning algorithm we show that the universality class of this phase transition can be tuned. The classes include d… ▽ More The facilitation of Rydberg excitations in a gas of atoms provides an ideal model system to study epidemic evolution on (dynamic) networks and self organization of complex systems to the critical point of a non-equilibrium phase transition. Using Monte-Carlo simulations and a machine learning algorithm we show that the universality class of this phase transition can be tuned. The classes include directed percolation (DP), the most common class in short-range spreading models, and mean-field (MF) behavior, but also different types of anomalous directed percolation (ADP), characterized by rare long-range excitation processes. In a frozen gas, ground state atoms that can facilitate each other form a static network, for which we predict DP universality. Atomic motion then turns the network into a dynamic one with long-range (Levy-flight type) excitations. This leads to continuously varying critical exponents corresponding to the ADP universality class, eventually reaching MF behavior. These findings also explain the recently observed critical exponent of Rydberg facilitation in an ultra-cold gas experiment [Helmrich et al., Nature 577, 481 (2020)], which was in between DP and MF values. △ Less

Submitted 25 April, 2024; originally announced April 2024.

Mean-field approach to Rydberg facilitation in a gas of atoms at high and low temperatures

Authors: Daniel Brady, Michael Fleischhauer

Abstract: The excitation spread caused by Rydberg facilitation in a gas of laser driven atoms is an interesting model system for studying epidemic dynamics. We derive a mean-field approach to describe this facilitation process in the limits of high and low temperatures, which takes into account Rydberg blockade and the network character of excitation spreading in a low-temperature gas. As opposed to previou… ▽ More The excitation spread caused by Rydberg facilitation in a gas of laser driven atoms is an interesting model system for studying epidemic dynamics. We derive a mean-field approach to describe this facilitation process in the limits of high and low temperatures, which takes into account Rydberg blockade and the network character of excitation spreading in a low-temperature gas. As opposed to previous mean-field models, our approach accurately predicts all stages of the facilitation dynamics from the initial fast epidemic growth, an extended saturation period, to the final relaxation phase. △ Less

Submitted 28 August, 2023; originally announced August 2023.

Comments: arXiv admin note: text overlap with arXiv:2302.14145

Griffiths Phase in a Facilitated Rydberg Gas at Low Temperature

Authors: Daniel Brady, Jana Bender, Patrick Mischke, Thomas Niederprüm, Herwig Ott, Michael Fleischhauer

Abstract: The spread of excitations by Rydberg facilitation bears many similarities to epidemics. Such systems can be modeled with Monte-Carlo simulations of classical rate equations to great accuracy as a result of high dephasing. In this paper, we analyze the dynamics of a Rydberg many-body system in the facilitation regime in the limits of high and low temperatures. While in the high-temperature limit a… ▽ More The spread of excitations by Rydberg facilitation bears many similarities to epidemics. Such systems can be modeled with Monte-Carlo simulations of classical rate equations to great accuracy as a result of high dephasing. In this paper, we analyze the dynamics of a Rydberg many-body system in the facilitation regime in the limits of high and low temperatures. While in the high-temperature limit a homogeneous mean-field behaviour is recovered, characteristic effects of heterogeneity can be seen in a frozen gas. At large temperatures the system displays an absorbing-state phase transition and, in the presence of an additional loss channel, self-organized criticality. In a frozen or low-temperature gas, excitations are constrained to a network resembling an Erdös-Renyi graph. We show that the absorbing-state phase transition is replaced with an extended Griffiths phase, which we accurately describe by a susceptible-infected-susceptible model on the Erdös-Renyi network taking into account Rydberg blockade. Furthermore, we expand upon an existing macroscopic Langevin equation to more accurately describe the density of Rydberg atoms in the frozen and finite temperature regimes. △ Less

Submitted 21 August, 2023; v1 submitted 27 February, 2023; originally announced February 2023.

Comments: 14 pages, 11 figures