Circular Rydberg states offer advantages for quantum information and quantum simulation platforms due to their long lifetimes and strong dipole-dipole interactions. Unfortunately, current techniques for the production of these states remain technically challenging. Here we investigate the ability of twisted electron collisions to produce circular Rydberg states. Twisted electrons carry quantized orbital angular momentum that can be transferred to the electronic state of the atom, potentially providing an efficient means to generate circular Rydberg states. Using a fully quantum mechanical framework, we compute total excitation cross sections for circular Rydberg states of hydrogen, rubidium, and cesium targets using Bessel electron beams. Our models account for the full Bessel-beam structure of the incident electron and incorporate macroscopic target effects to model experimentally-relevant conditions. Our results show that twisted electrons with large opening angles produce significant enhancements in the excitation probability relative to plane-wave electrons, particularly for large opening angles and low energies. We trace this enhancement to contributions from projectiles with large values of orbital angular momentum. These findings demonstrate that twisted-electron excitation may provide a feasible and potentially advantageous pathway for generating circular Rydberg states.
Circular Rydberg states offer advantages for quantum information and quantum simulation platforms due to their long lifetimes and strong dipole-dipole interactions. Unfortunately, current techniques for the production of these states remain technically challenging. Here we investigate the ability of twisted electron collisions to produce circular Rydberg states. Twisted electrons carry quantized orbital angular momentum that can be transferred to the electronic state of the atom, potentially providing an efficient means to generate circular Rydberg states. Using a fully quantum mechanical framework, we compute total excitation cross sections for circular Rydberg states of hydrogen, rubidium, and cesium targets using Bessel electron beams. Our models account for the full Bessel-beam structure of the incident electron and incorporate macroscopic target effects to model experimentally-relevant conditions. Our results show that twisted electrons with large opening angles produce significant enhancements in the excitation probability relative to plane-wave electrons, particularly for large opening angles and low energies. We trace this enhancement to contributions from projectiles with large values of orbital angular momentum. These findings demonstrate that twisted-electron excitation may provide a feasible and potentially advantageous pathway for generating circular Rydberg states.
Abstract Circular Rydberg states offer advantages for quantum information and quantum simulation platforms due to their long lifetimes and strong dipole–dipole interactions. Unfortunately, current techniques for the production of these states remain technically challenging. Here we investigate the ability of twisted electron collisions to produce circular Rydberg states. Twisted electrons carry quantized orbital angular momentum (OAM) that can be transferred to the electronic state of the atom, potentially providing an efficient means to generate circular Rydberg states. Using a fully quantum mechanical framework, we compute total excitation cross sections for circular Rydberg states of hydrogen, lithium, rubidium, and cesium targets using Bessel electron beams. Our models account for the full Bessel-beam structure of the incident electron and incorporate macroscopic target effects to model experimentally-relevant conditions. Our results show that twisted electrons with large opening angles produce significant enhancements in the excitation probability relative to plane-wave electrons, particularly for large opening angles and low energies. We trace this enhancement to contributions from projectiles with large values of OAM. These findings demonstrate that twisted-electron excitation may provide a feasible and potentially advantageous pathway for generating circular Rydberg states.
Summary form only given. Quantum simulation offers a highly promising way to understand large correlated quantum systems, and many experimental platforms are now being developed. Rydberg atoms are specially appealing thanks to their strong and short-range dipole-dipole interaction and to their long lifetime. Low-angular momentum Rydberg atoms have been successfully used recently to realize early quantum simulators. These experiments suffer, however, from the limited (despite long) lifetime of these levels and the fact that they cannot be efficiently trapped [1, 2].Here, we propose to use circular Rydberg atoms, i.e., Rydberg atoms with maximum angular momentum, to realize a quantum simulator: A chain of circular atoms is laser trapped inside a spontaneous emission inhibiting structure. A defect-free chain of 40 atoms could be prepared. It is expected to live several seconds inside the inhibition structure. Given the strong interaction frequencies between nearby Rydberg atoms, such a system would, thus, allow us to observe the dynamics of the spin chain over several 10 4 interaction cycles. In addition, the solid state Hamiltonian that would be simulated is fully tuneable experimentally. The proposed circular atoms quantum simulator should therefore open the way towards the simulations of systems and of their dynamics beyond the grasp of classical computation.
Summary form only given. Condensed-matter systems are interesting and important to understand, for fundamental science as well as towards more applied objectives in the development of new materials for instance. Unfortunately, these many-body quantum systems are difficult to study: both the theoretical approach and the numerical simulation are proving impossible to carry out to relevant system sizes. Quantum simulation proposes to mimic those out-of-reach systems with more controllable and accessible quantum systems. Rydberg atoms gained renewed interest in the last decades thanks to their very high polarizability, allowing for strong and tunable short-range interactions. They constitute an interesting candidate for a quantum simulation platform. However, low angular momentum Rydberg states have limited, despite relatively long, lifetimes which limit the scope of such a quantum simulator. Moreover, low-l Rydberg states cannot be efficiently laser-trapped. In order to overcome these limitations, we propose to use circular Rydberg states, i.e., of maximum angular momentum. Circular Rydberg states exhibit much longer lifetimes, and can be trapped using laser light. By placing the circular Rydberg atoms inside a spontaneous emission-inhibiting capacitor, we hope to achieve the deterministic preparation of a 1D-chain of 40 atoms, with a collective lifetime of over 2 seconds. With expected exchange energies in the 10-100 kHz range, this would provide a platform capable of simulating quantum many-body physics up to 105exchange times. The first step towards the experimental realization of such a quantum simulator is the demonstration of the laser-trapping of circular Rydberg atoms. To this end, we use a Laguerre-Gauss hollow beam at 1064 nm, imposing a ponderomotive potential on the nearly-free electron of the Rydberg atoms. I will present our latest experimental results of light-trapping of circular Rydberg atoms.
Assemblies of interacting Rydberg atoms show promise for the quantum simulation of transport phenomena, quantum chemistry, and condensed-matter systems. Such schemes are typically limited by the finite lifetime of Rydberg states. Circular Rydberg states have the longest lifetimes among Rydberg states but lack the energetic isolation in the spectrum characteristic of low-angular-momentum states. The latter is required to obtain simple transport models with few electronic states per atom. Simple models can, however, even be realized with circular states by exploiting dipole-dipole selection rules or external fields. We show here that this approach can be particularly fruitful for scenarios where quantum transport is coupled to atomic motion, such as adiabatic excitation transport or quantum simulations of electron-phonon coupling in light harvesting. Additionally, we explore practical limitations of flexible Rydberg aggregates with circular states and to which extent interactions among circular Rydberg atoms can be described using classical models.
Stability achieved by large angular momentum is ubiquitous in nature, with examples ranging from classical mechanics, over optics and chemistry, to nuclear physics. In atoms, angular momentum can protect excited electronic orbitals from decay due to selection rules. This manifests spectacularly in highly excited Rydberg states. Low angular momentum Rydberg states are at the heart of recent breakthroughs in quantum computing, simulation and sensing with neutral atoms. For these applications the lifetime of the Rydberg levels sets fundamental limits for gate fidelities, coherence times, or spectroscopic precision. The quest for longer Rydberg state lifetimes has motivated the generation, coherent control and trapping of circular Rydberg atoms, which are characterized by the maximally allowed electron orbital momentum and were key to seminal experiments with single atoms and photons. Here, we report the observation of individually trapped circular Rydberg atoms with lifetimes of more than 10 milliseconds, two orders of magnitude longer-lived than the established low angular momentum orbitals. This is achieved via Purcell suppression of blackbody modes at room temperature. We coherently control individual circular Rydberg levels at so far elusive principal quantum numbers of up to n = 103, and observe tweezer trapping of the Rydberg atoms on the hundred millisecond scale. Our results pave the way for quantum information processing and sensing utilizing the combination of extreme lifetimes and giant Rydberg blockade.
In this dissertation I investigate cold Rydberg atoms and molecules in which the angular-momentum character of the quantum states involved strongly influences their properties and dynamics. In the first part I focus on long-range diatomic Rydberg molecules formed by a rubidium D-state Rydberg atom and a second rubidium atom in its ground state. Spectroscopic measurements of molecular binding energies are presented showing the effect of the Rydberg atom size and fine-structure coupling on the molecular potentials. A theoretical model is introduced that takes into account all relevant angular-momentum couplings between the molecular constituents, successfully reproducing experimental observations. Calculations of adiabatic potentials and binding energies, molecular-state lifetimes, electric and magnetic dipole moments are also presented. In the second part, I describe the production and magnetic trapping of cold circular Rydberg atoms. The circular Rydberg atoms are generated out of a cold gas of rubidium using the crossed-fields method and magnetically trapped. The trapping force is employed to induce center-of-mass oscillations of the trapped atom sample. Trap parameters and observed oscillation frequencies are used to measure the magnetic moments of the circular Rydberg atoms. Trap losses and the atomic internal-state evolution in the 300 Kelvin thermal background are also investigated.