Engineering continuous, high-flux, and collimated atomic beams is a useful resource for metrology and material deposition. Developments in this area have been essential for the evolution of cold-atom based quantum experiments, yet the ubiquitous balanced-force methods such as transverse molasses cooling degrade at high atomic flux due to absorption-induced force imbalance. We introduce a collimation scheme that combines the use of a broadband transition for velocity shifting with a narrowband transition for velocity selection, enabling velocity-selective beam collimation without relying on balanced-power counter-propagating beams. Collimated atoms are shelved in a long-lived internal state, reducing the total light scattering and providing a state-heralded collimated beam. Simulations using strontium as a model system show a highly effective collimation process that does not suffer from absorption-induced force-imbalance and experimental results agree well with these predictions.

We directly observe and spatially map an optical analog of the Magnus effect, where intrinsic spin-orbit-like coupling of light generates a spin-dependent transverse displacement of the atom-light interaction profile for a ^{40}Ca^{+} ion. Probed on a quadrupole transition using a tightly focused beam, we observe displacements of the maximum in the profile of the effective interaction by several 100 nm originating from intrinsic longitudinal electric field components beyond the paraxial approximation. The tight focus of the beam induces additional transverse polarization gradients, which we characterize through a phase-sensitive measurement and spatial maps for different beam configurations. The results establish the physical basis of polarization-gradient interactions relevant to optical tweezer-based quantum control.

Tightly focused laser beams, or optical tweezers, are essential for analog and digital quantum simulation with neutral atoms and trapped ions. Despite this, most of the current intuition and theoretical treatment utilizes the paraxial approximation, which is an insufficient description at the focus of tightly focused optical tweezers. We develop an analytic model, which we use in tandem with numerical simulations, to quantify how nonparaxial effects will manifest in the next generation of scalable quantum hardware, where tightly focused beams are used for individual qubit control. In particular, we calculate the light potentials of Gaussian and Laguerre-Gaussian beams driving the quadrupole 2S1/2 -> 2D5/2 transition in 40Ca+. Longitudinal field components in the beam center cause spatially dependent Rabi frequencies and ac Stark shifts, leading to unexpected qubit-motion coupling. We characterize single-and two-qubit gate infidelities due to this effect with an analytic model and numerical simulation. We identify regimes where nonparaxial effects should be taken into account for high-precision quantum control, and highlight that the effects are potentially more severe for the case of neutral atom and molecule addressing.

Rydberg atoms trapped by optical tweezers have emerged as a versatile platform to emulate lattices with different geometries, in which long-range interacting spins lead to fascinating phenomena, ranging from spin liquids to topological states of matter. Here, we show that when the lattice has a fractal geometry with Hausdorff dimension 1.58, additional surprises appear. The system is described by a transverse-field Ising model with long-range van der Waals interactions in a Sierpinski gasket fractal. We investigate the problem theoretically using exact diagonalization, variational mean field, quantum Monte Carlo, and a graph-based numerical technique, SIM-GRAPH, which we developed. We find that in the quantum regime, the phase diagram exhibits phases in which the spins flip one-by-one. The theoretical results are in excellent agreement with experiments performed with single 88Sr atoms trapped by optical tweezers arranged in a fractal geometry. The magnetization and von Neumann entanglement entropy reveal several regimes in which single spin-flips are delocalized over many sites of one sublattice, thus allowing for an unprecedented control of a cascade of phase transitions in a manybody system. These results expand the possibilities of Rydberg atoms for quantum information processing and may have profound implications in quantum technology.

We present fast parallel rearrangement of single atoms in optical tweezers into arbitrary geometries by updating holograms displayed by an ultra fast spatial light modulator. Using linear interpolation of the tweezer position and the optical phase between the start and end arrays, we can calculate and display holograms every few ms, limited by technology. To show the versatility of our method, we sort the same atomic sample into multiple geometries with success probabilities of 0.996(2) per rearrangement cycle. This makes the method a useful tool for rearranging large atom arrays for quantum computation and quantum simulation.

We present a general method for engineering qudits through individually addressable transitions between Zeeman sublevels, achieved by combining a large linear Zeeman shift with a state-dependent light shift. This approach lifts the degeneracy between adjacent states while simultaneously tuning their energy splittings into the radio-frequency (RF) domain, enabling coherent manipulation within the Zeeman manifold using experimentally accessible drive frequencies. As a concrete realization, we investigate the implementation of an SU(5) quintet encoded in the Zeeman sublevels of the long-lived ^3P_2 state of neutral ^88Sr atoms confined in far-detuned, σ^--polarized optical tweezers. Using realistic experimental parameters, we numerically demonstrate full control of the quintet manifold, including initialization into a specific SU(5) basis state via a multi-photon transfer, coherent state- and site-selective single-qudit rotations driven by RF fields, and fast state-selective optical readout. Our simulations predict state-preparation fidelities of ℱ≃ 0.99 within ∼ 1 μs, single-qudit gate fidelities of ℱ≃ 0.99 with π-pulse durations of ∼ 2.5 μs, and fast destructive imaging with durations below 10 μs. These results establish a broadly applicable framework for high-fidelity control of Zeeman sublevel-encoded qudits and highlight the ^3P_2 manifold in strontium as a promising platform for scalable qudit-based quantum technologies.

We consider the quantum simulation of quadratic spin-phonon coupling in a crystal of trapped ions. The coupling is implemented using tightly focused optical tweezers on each ion that change the local trapping potential in a state-dependent way. By encoding spins in the internal states of the ions and adding a tunneling term via M & oslash;lmer-S & oslash;rensen-type interactions, we calculate the emergence of mobile bipolarons driven by the zero-point energy of the ion crystal phonons. We show that thermal occupation may pin the bipolarons for ion crystals at finite temperature. Our scheme can be used to study and illustrate the emergence of mobile bipolarons as a function of temperature.

We discuss the use of optical tweezers for two-qubit gates on trapped ions in a crystal. Qubit-state dependent forces arise from polarization gradients near the focus. We simulate gate infidelities of ~10 −3 .

We consider the implementation of quantum logic gates in trapped ions using tightly focused optical tweezers. Strong polarization gradients near the tweezer focus lead to qubit-state-dependent forces on the ion. We show that these may be used to implement quantum logic gates on pairs of ion qubits in a crystal. The qubit-state-dependent forces generated by this effect are located on the plane perpendicular to the direction of propagation of the laser beams opening alternate ways of coupling to motional modes of an ion crystal. The proposed gate does not require ground-state cooling of the ions although the waist of the tightly focused beam needs to be comparable to its wavelength in order to achieve the needed field curvature. Furthermore, the gate can be implemented on both ground-state and magnetic-field-insensitive clock-state qubits without the need for counterpropagating laser fields. This simplifies the setup and eliminates errors due to phase instabilities between the gate laser beams. Finally, we show that imperfections in the gate execution, in particular, a 30-nm tweezer alignment error, lead to an infidelity of <^>10-3. In the absence of experimental imperfections and within the limits of the gate model explored in this paper the fidelity is predicted to be <^>0.999 88 when using a Laguerre-Gaussian beam to suppress photon scattering errors.

We consider the implementation of quantum logic gates in trapped ions using tightly focused optical tweezers. Strong polarization gradients near the tweezer focus lead to qubit-state dependent forces on the ion. We show that these may be used to implement quantum logic gates on pairs of ion qubits in a crystal. The qubit-state dependent forces generated by this effect live on the plane perpendicular to the direction of propagation of the laser beams opening new ways of coupling to motional modes of an ion crystal. The proposed gate does not require ground state cooling of the ions and does not rely on the Lamb-Dicke approximation, although the waist of the tightly focused beam needs to be comparable with its wavelength in order to achieve the needed field curvature. Furthermore, the gate can be performed on both ground state and magnetic field insensitive clock state qubits without the need for counter-propagating laser fields. This simplifies the setup and eliminates errors due to phase instabilities between the gate laser beams. Finally, we show that imperfections in the gate execution, in particular pointing errors $<30$ nm in the tweezers reduce the gate fidelity from $\mathcal F\gtrsim 0.99998$ to $\gtrsim 0.999$.

Single strontium atoms held in optical tweezers have so far only been imaged using the broad $^{1\hspace{-0.3ex}}S_0$-$^{1\hspace{-0.3ex}}P_1$ transition. For Yb, use of the narrow (183 kHz-wide) $^{1\hspace{-0.3ex}}S_0$-$^{3\hspace{-0.3ex}}P_1$ transition for simultaneous imaging and cooling has been demonstrated in tweezers with a magic wavelength for the imaging transition. We demonstrate high-fidelity imaging of single Sr atoms using its even narrower (7.4 kHz-wide) $^{1\hspace{-0.3ex}}S_0$ - $^{3\hspace{-0.3ex}}P_1$ transition. The atoms are trapped in \textit{non}-magic-wavelength tweezers. We detect the photons scattered during Sisyphus cooling, thus keeping the atoms near the motional ground state of the tweezer throughout imaging. The fidelity of detection is 0.9991(4) with a survival probability of 0.97(2). An atom in a tweezer can be held under imaging conditions for 79(3) seconds allowing for hundreds of images to be taken, limited mainly by background gas collisions. We detect atoms in an arrary of 36 tweezers with 813.4-nm light and trap depths of 135(20) $\mu$K. This trap depth is three times shallower than typically used for imaging on the broad $^{1\hspace{-0.3ex}}S_0$ - $^{1\hspace{-0.3ex}}P_1$ transition. Narrow-line imaging opens the possibility to even further reduce this trap depth, as long as all trap frequencies are kept larger than the imaging transition linewidth. Imaging using a narrow-linewidth transition in a non-magic-wavelength tweezer also allows for selective imaging of a given tweezer. As a demonstration, we selectively image (hide) a single tweezer from the array. This provides a useful tool for quantum error correction protocols.

Abstract The insight that optical vortex beams carry orbital angular momentum (OAM), which emerged in Leiden about 30 years ago, has since led to an ever expanding range of applications and follow-up studies. This paper starts with a short personal account of how these concepts arose. This is followed by a description of some recent ideas where the coupling of transverse orbital and spin angular momentum (SAM) in tightly focused laser beams produces interesting new effects. The deflection of a focused light beam by an atom in the focus is reminiscent of the Magnus effect known from aerodynamics. Momentum conservation dictates an accompanying light force on the atom, transverse to the optical axis. As a consequence, an atom held in an optical tweezer will be trapped at a small distance of up to λ/2π away from the optical axis, which depends on the spin state of the atom and the magnetic field direction. This opens up new avenues to control the state of motion of atoms in optical tweezers as well as potential applications in quantum gates and interferometry.

Jordi R. Weggemans, 2 Alexander Urech, 2 Alexander Rausch, Robert Spreeuw, 2 Richard Boucherie, Florian Schreck, 2 Kareljan Schoutens, 2 Jǐŕı Minář, 2 and Florian Speelman 2 CWI, Science Park 123, 1098 XG Amsterdam, The Netherlands QuSoft, Science Park 123, 1098 XG Amsterdam, The Netherlands Van der Waals-Zeeman Institute, Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, the Netherlands Robert Bosch GmbH, Corporate Research, Robert-Bosch-Campus 1, 71272 Renningen, Germany Stochastic Operations Research, Department of Applied Mathematics, University of Twente, 7500 AE, Enschede, The Netherlands. Institute for Theoretical Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, the Netherlands Informatics Institute, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, the Netherlands (Dated: July 13, 2021)

It is shown that a circular dipole can deflect the focused laser beam that induces it and will experience a corresponding transverse force. Quantitative expressions are derived for Gaussian and angular top hat beams, while the effects vanish in the plane wave limit. The phenomena are analogous to the Magnus effect, pushing a spinning ball onto a curved trajectory. The optical case originates in the coupling of spin and orbital angular momentum of the dipole and the light. In optical tweezers the force causes off-axis displacement of the trapping position of an atom by a spin-dependent amount up to λ/2π, set by the direction of a magnetic field. This suggests direct methods to demonstrate and explore these effects, for instance, to induce spin-dependent motion.

Coherently manipulating Rydberg atoms in mesoscopic systems has proven challenging due to the unwanted population of nearby Rydberg levels by black-body radiation. Recently, there have been some efforts towards understanding these effects using states with a low principal quantum number that only have resonant dipole-dipole interactions. We perform experiments that exhibit black-body-induced dipole-dipole interactions for a state that also has a significant van der Waals interaction. Using an enhanced rate-equation model that captures some of the long-range properties of the dipolar interaction, we show that the initial degree of Rydberg excitation is dominated by the van der Waals interaction, while the observed linewidth at later times is dominated by the dipole-dipole interaction. We also point out some prospects for quantum simulation.

We observe a density-dependent collective suppression of optical pumping between the hyperfine ground states in an array of submicrometer-sized clouds of cold rubidium atoms. The suppressed Raman transition rate can be explained by strong resonant dipole-dipole interactions that are enhanced by increasing atom density. The observations are consistent with stochastic electrodynamics simulations that incorporate the effects of the nonlinear population transfer via internal atomic levels embedded in a coupled-dipole model.

We have designed and realized magnetic trapping geometries for ultracold atoms based on permanent magnetic films. Magnetic chip based experiments give a high level of control over trap barriers and geometric boundaries in a compact experimental setup. These structures can be used to study quantum spin physics in a wide range of energies and length scales. By introducing defects into a triangular lattice, kagome and hexagonal lattice structures can be created. Rectangular lattices and (quasi-)one-dimensional structures such as ladders and diamond chain trapping potentials have also been created. Quantum spin models can be studied in all these geometries with Rydberg atoms, which allow for controlled interactions over several micrometers. We also present some nonperiodic geometries where the length scales of the traps are varied over a wide range. These tapered structures offer another way to transport large numbers of atoms adiabatically into subwavelength traps and back.

We explore the possibility to trap Rydberg atoms in tightly confining magnetic microtraps. The trapping frequencies for Rydberg atoms are expected to be influenced strongly by magnetic-field gradients. We show that there are regimes where Rydberg atoms can be trapped. Moreover, we show that so-called magic trapping conditions can be found for certain states of rubidium, where both Rydberg atoms and ground-state atoms have the same trapping frequencies. Magic trapping is highly beneficial for implementing quantum gate operations that require long operation times.

Experiments handling Rydberg atoms near surfaces must necessarily deal with the high sensitivity of Rydberg atoms to (stray) electric fields that typically emanate from adsorbates on the surface. We demonstrate a method to modify and reduce the stray electric field by changing the adsorbate distribution. We use one of the Rydberg excitation lasers to locally affect the adsorbed dipole distribution. By adjusting the averaged exposure time we change the strength (with the minimal value less than 0.2 V/cm at 78 mu m from the chip) and even the sign of the perpendicular field component. This technique is a useful tool for experiments handling Rydberg atoms near surfaces, including atom chips.

We report on the epitaxial growth and the characterization of thin FePt films and the subsequent patterning of magnetic lattice structures. These structures can be used to trap ultracold atoms for quantum simulation experiments. We use molecular beam epitaxy to deposit monocrystalline FePt films with a thickness of 50 nm. The films are characterized with X-ray scattering and Mossbauer spectroscopy to determine the long range order parameter and the hard magnetic axes. A high monocrystalline fraction was measured as well as a strong remanent magnetization of M = 900 kA/m and coercivity of 0.4 T. Using electron beam lithography and argon ion milling, we create lattice patterns with a period down to 200 nm, and a resolution of 30 nm. The resulting lattices are imaged in a scanning electron microscope in the cross-section created by a focused ion beam. A lattice with continuously varying lattice constant ranging from 5 pm down to 250 nm has been created to show the wide range of length scales that can now be created with this technique. (C) 2018 Author(s).