We demonstrate single-atom trapping in two-dimensional arrays of microtraps with arbitrary geometries. We generate the arrays using a spatial light modulator, with which we imprint an appropriate phase pattern on an optical dipole-trap beam prior to focusing. We trap single 87 Rb atoms in the sites of arrays containing up to approximately 100 microtraps separated by distances as small as 3 μm, with complex structures such as triangular, honeycomb, or kagome lattices. Using a closed-loop optimization of the uniformity of the trap depths ensures that all trapping sites are equivalent. This versatile system opens appealing applications in quantum-information processing and quantum simulation, e.g., for simulating frustrated quantum magnetism using Rydberg atoms.

We report the direct measurement of the van der Waals interaction between two isolated, single Rydberg atoms separated by a controlled distance of a few micrometers. Working in a regime where the single-atom Rabi frequency for excitation to the Rydberg state is comparable to the interaction, we observe partial Rydberg blockade, whereby the time-dependent populations of the various two-atom states exhibit coherent oscillations with several frequencies. Quantitative comparison of the data with a simple model based on the optical Bloch equations allows us to extract the van der Waals energy, and observe its characteristic C6/R6 dependence. The measured C6 coefficients agree well with ab initio calculations, and we observe their dramatic increase with the principal quantum number n of the Rydberg state.

We study the Rydberg blockade in a system of three atoms arranged in different 2D geometries (linear and triangular configurations). In the strong blockade regime, we observe high-contrast, coherent collective oscillations of the single excitation probability, and an almost perfect van der Waals blockade. Our data is consistent with a total population in doubly and triply excited states below 2 %. In the partial blockade regime, we directly observe the anisotropy of the van der Waals interactions between |nD Rydberg states in the triangular configuration. A simple model, that only uses independently measured two-body van der Waals interactions, fully reproduces the dynamics of the system without any adjustable parameter. These results are extremely promising for scalable quantum information processing and quantum simulation with neutral atoms.PACS numbers: 03.67. Bg,32.80.Ee,34.20.Cf Engineering quantum many-body systems with a high degree of control and tunable interactions is an active field of research as it is a prerequisite for quantum information processing [1] and quantum simulation [2]. Recently, significant achievements have been obtained towards this goal, e.g. using trapped ions for simulating quantum magnetism [3][4][5]. Another platform considered for such tasks consists of systems of neutral Rydberg atoms interacting via the strong and controllable long-range dipole-dipole interaction, which is responsible for the Rydberg blockade [6][7][8][9]. Through this mechanism, multiple excitations with a resonant narrow-band laser are inhibited within a blockade sphere by RydbergRydberg interactions. The dipole blockade provides a way to realize fast quantum gates and to entangle particles, as demonstrated for two atoms [10,11]. This mechanism can in principle be extended to an ensemble of N atoms, with fascinating applications in quantum state engineering [12].Although the picture of a blockade sphere has been remarkably successful at describing many recent experiments [1,[13][14][15][16][17][18][20][21][22], some theoretical works question this simple approach. Even for the case of N = 3, some situations have been identified where nearly resonant dipole-dipole interactions [23], the non-additivity of the van der Waals potentials [24], or the anisotropy of the interactions [25] lead to the breakdown or reduction of the blockade.In this Letter, we show that, for experimentally relevant parameters, the Rydberg blockade is robust in ensembles of three atoms. In particular, we consider two different arrangements, namely, a line and an equilateral triangle. We observe an almost perfect van der Waals blockade and the coherent collective behavior of Rydberg excitations in both configurations. To go beyond this observation and understand the dynamics of the system in detail, we measure the angular dependence of the effec- tive interaction energy V eff between two single-atoms excited to |r ≡ |nD 3/2 , m j = 3/2 Rydberg states. Using the measured two-body interaction strength we demonstrate that it is possible t...

Laser-plasma acceleration [1,2] is an emerging technique for accelerating electrons to high energies over very short distances. The accelerated electron bunches have femtosecond duration [3,4], making them particularly relevant for applications such as ultrafast imaging [5] or femtosecond X-ray generation [6,7]. Current laser-plasma accelerators are typically driven by Joule-class laser systems that have two main drawbacks: their relatively large scale and their low repetition-rate, with a few shots per second at best. The accelerated electron beams have energies ranging from 100 MeV [8][9][10] to multi-GeV [11,12], however a MeV electron source would be more suited to many societal and scientific applications. Here, we demonstrate a compact and reliable laserplasma accelerator producing high-quality few-MeV electron beams at kilohertz repetition rate.This breakthrough was made possible by using near-single-cycle light pulses, which lowered the required laser energy for driving the accelerator by three orders of magnitude, thus enabling high repetition-rate operation and dramatic downsizing of the laser system. The measured electron bunches are collimated, with an energy distribution that peaks at 5 MeV and contains up to 1 pC of charge. Numerical simulations reproduce all experimental features and indicate that the electron bunches are only ∼ 1 fs long. We anticipate that the advent of these kHz femtosecond relativistic electron sources will pave the way to wide-impact applications, such as ultrafast electron diffraction in materials [13,14] In a laser-plasma accelerator, a laser pulse is focused to ultra-high intensity in an underdense plasma. The laser ponderomotive force sets up a charge separation in the plasma by displacing electrons, resulting in the excitation of a large-amplitude plasma wave, also called a wakefield. The wakefield carries enormous electric fields, in excess of 100 GV/m [16], that are well adapted for accelerating electrons to relativistic energies over short distances, typically less than a millimeter. The accelerated electron beams have femtosecond duration and are intrinsically synchronized to the laser pulse, which could lift the temporal resolution bottleneck in various experimental situations. For example, in ultrafast electron diffraction, the temporal resolution is currently limited to more than 100 fs, but it could be improved to sub-10 fs using laser driven electrons [15]. Thus, laser-plasma accelerators in the MeV range could find numerous applications with unprecedented time resolution, provided they operate reliably and at high repetition-rate. Indeed, in addition to temporal resolution, ultrafast imaging and diffraction also require statistics and a high signal-to-noise ratio [5,14] that can only be reached with a reliable and high repetition-rate electron source.In this letter, we demonstrate reliable operation of a laser-plasma accelerator delivering 5 MeV electrons at kHz repetition-rate. This breakthrough was made possible by the original use of a multi-mJ lase...

Accelerating particles to relativistic energies over very short distances using lasers has been a long standing goal in physics. Among the various schemes proposed for electrons, vacuum laser acceleration has attracted considerable interest and has been extensively studied theoretically because of its appealing simplicity: electrons interact with an intense laser field in vacuum and can be continuously accelerated, provided they remain at a given phase of the field until they escape the laser beam. But demonstrating this effect experimentally has proved extremely challenging, as it imposes stringent requirements on the conditions of injection of electrons in the laser field. Here, we solve this long-standing experimental problem for the first time by using a plasma mirror to inject electrons in an ultraintense laser field, and obtain clear evidence of vacuum laser acceleration.With the advent of PetaWatt class lasers, this scheme could provide a competitive source of very high charge (nC) and ultrashort relativistic electron beams.1 arXiv:1511.05936v1 [physics.plasm-ph] 18 Nov 2015Femtosecond lasers currently achieve light intensities at focus that far exceed 10 18 W/cm 2 at near infrared wavelengths [1]. One of the great prospects of these extreme intensities is the laser-driven acceleration of electrons to relativistic energies within very short distances.At present, the most advanced scheme consists of using ultraintense laser pulses to excite large amplitude wakefields in underdense plasmas, providing extremely high accelerating gradients in the order of 100 GV/m [2]. However, over the past decades, the direct acceleration of electrons by light in vacuum has also attracted considerable interest and has been extensively studied theoretically [3][4][5][6][7][8][9][10][11]. These investigations have been driven by the fundamental interest of this most elementary interaction, and by its potential for extreme electron acceleration through electric fields of > 10's TV/m that ultraintense laser pulses provide.The underlying idea is to inject free electrons into an ultraintense laser field so that they always remain within a given half optical cycle of the field, where they constantly gain energy until they leave the focal volume. 1D Analytical calculations [3] show that for relativistic electrons, the maximum energy gain from this process is ∆E ∝ mc 2 γ 0 a 2 0 , where γ 0 is the electron initial Lorentz factor, and a 0 is the normalized laser vector potential, m the electron mass, and c the vacuum light velocity. Reaching high energy gains thus requires high initial energies γ 0 1 and/or ultrahigh laser amplitudes (a 0 1).In contrast with the large body of theoretical work published on this vacuum laser acceleration (VLA) of electrons to relativistic energies, experimental observations have largely remained elusive [12][13][14][15][16][17] -sometimes even controversial [18,19]-and have so far not demonstrated significant energy gains. This is because VLA occurs efficiently only for electrons injected in t...

This review presents the technological infrastructure that will be available at the Extreme Light Infrastructure Attosecond Light Pulse Source (ELI-ALPS) international facility. ELI-ALPS will offer to the international scientific community ultrashort pulses in the femtosecond and attosecond domain for time-resolved investigations with unprecedented levels of high quality characteristics. The laser sources and the attosecond beamlines available at the facility will make attosecond technology accessible for scientists lacking access to these novel tools. Time-resolved

We demonstrate highly efficient generation of coherent 420 nm light via up-conversion of near-infrared lasers in a hot rubidium vapor cell. By optimizing pump polarizations and frequencies we achieve a single-pass conversion efficiency of 260% per Watt, significantly higher than in previous experiments. A full exploration of the coherent light generation and fluorescence as a function of both pump frequencies reveals that coherent blue light is generated close to (85)Rb two-photon resonances, as predicted by theory, but at high vapor pressure is suppressed in spectral regions that do not support phase matching or exhibit single-photon Kerr refraction. Favorable scaling of our current 1 mW blue beam power with additional pump power is predicted.

We report on recent progress on laser-plasma acceleration using a low energy and high-repetition rate laser system. Using only few milliJoule laser energy, in conjunction with extremely short pulses composed of a single optical cycle, we demonstrate that the laser-plasma accelerator (LPA) can be operated close to the resonant blowout regime. This results in the production of high charge electron beams (>10 pC) with peaked energy distributions in the few MeV range and relatively narrow divergence angles. We highlight the importance of the plasma density profile and gas jet design for the performance of the LPA. In this extreme regime of relativistic laser-plasma interaction with near-single-cycle laser pulses, we find that the effect of group velocity dispersion and carrier envelope phase can no longer be neglected. These advances bring LPAs closer to real scientific applications in ultrafast probing.