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We report on the implementation of an optical tweezer system for controlled transport of ultracold atoms along a narrow, static confinement channel. The tweezer system is based on high-efficiency acousto-optical deflectors and offers two-dimensional control over beam position. This opens up the possibility for tracking the transport channel when shuttling atomic clouds along the guide, forestalling atom spilling. Multiple clouds can be tracked independently by time-shared tweezer beams addressing individual sites in the channel. The deflectors are controlled using a multichannel direct digital synthesizer, which receives instructions on a sub-microsecond time scale from a field-programmable gate array. Using the tweezer system, we demonstrate sequential binary splitting of an ultracold 87 Rb cloud into 2 5 clouds. Many applications in cold atom quantum technology require control over the positions and momenta of atomic clouds or single atoms. The ability to precisely move clouds of atoms around in space may, for example, unlock their use as probes for sampling surfaces and microscopic structures [1] or for mapping out magnetic fields [2]. Several protocols for quantum information processing rely on deterministic rearrangement and controlled transport of neutral atoms [3], where, e.g., quantum logic gates can be formed through the precise movement of atomic qubits [4]. Transport of atoms also emerges as a crucial step in the everyday operation of contemporary cold atom experiments for the purpose of shuttling atoms to a region of higher vacuum or increased optical access [5][6][7][8].Techniques for confining and manipulating polarizable particles by means of optical dipole forces from far-detuned laser beams have gained interdisciplinary importance after the seminal work of Ashkin, with applications ranging from folding of DNA to single atom trapping [9]. A focused reddetuned laser beam acts as an optical tweezer, trapping atoms at the waist [10]. By actively shifting the laser beam focus axially [6] or by steering the laser beam transversely [4,11], the positions of atoms may be controlled; we note that steering can also be accomplished using blue-detuned light [2,12]. Steerable tweezers have been widely applied, particularly within the field of micro-and biological particles. The figures-of-merit of various approaches are, for example, reviewed in [13]. Devices for tweezer steering include galvo and piezo-deflected mirrors, electro-optic deflectors, acousto-optic deflectors (AODs), as well as spatial light modulators. In the context of micro-and biological particles, manipulation of multiple optical traps was first demonstrated two decades ago using time-averaged confinement * Corresponding author: niels.kjaergaard@otago.ac.nz from a rapidly galvo scanned laser beam [14,15]. Work using AODs [16] for time-averaged confinement quickly followed and was successfully extended to micromanipulation of ultracold atoms in multiplexed discrete traps (up to three) [17] and for "painting" arbitrary potentials [18].In this ...

Solitons are long-lived wavepackets that propagate without dispersion and exist in a wide range of onedimensional (1D) nonlinear systems. A Bose-Einstein condensate trapped in a quasi-1D waveguide can support bright-solitary-matter waves (3D analogues of solitons) when interatomic interactions are sufficiently attractive that they cancel dispersion. Solitary-matter waves are excellent candidates for a new generation of highly sensitive interferometers, as their non-dispersive nature allows them to acquire phase shifts for longer times than conventional matter-waves interferometers. However, such an interferometer is yet to be realised experimentally. In this work, we demonstrate the splitting and recombination of a bright-solitary-matter wave on a narrow repulsive barrier, which brings together the fundamental components of an interferometer. We show that both interference-mediated recombination and classical velocity filtering effects are important, but for a sufficiently narrow barrier interference-mediated recombination can dominate. We reveal the extreme sensitivity of interference-mediated recombination to the experimental parameters, highlighting the potential of soliton interferometry.Bright-solitary waves, referred to as solitons in this work, are wavepackets that propagate in a quasi-1D geometry without dispersion, owing to a self-focussing nonlinearity. They are of fundamental interest in a broad range of settings due to their ubiquity in nonlinear systems, which occur prolifically in nature 1, 2 . In Bose-Einstein 1 arXiv:1906.06083v1 [cond-mat.quant-gas] 14 Jun 2019 condensates (BECs) the nonlinearity is provided by interatomic interactions governed by the s-wave scattering length, which can be tuned using a magnetic Feshbach resonance 3 . Bright solitons in BECs of 7 Li, 85 Rb, 39 K and 133 Cs have so far been experimentally demonstrated 4-10 . Understanding and probing the coherent phase carried by matter-wave solitons is an area of particular relevance for BEC physics, both because it is important in determining the stability of soliton-soliton collisions 10-14 and because there is a great interest in using solitons for atom interferometry 15-22 .Matter-wave interferometers have emerged as a means of achieving unprecedented sensitivity in interferometric measurements 23-26 . However, they have typically been limited by either interatomic collisions or dispersion of the atomic wavepackets, which cause dephasing and a reduced signal to noise, respectively 27 . Previous works have successfully reduced the impact of interatomic collisions through the control of interatomic interactions 28, 29 , or by generating squeezed states 30, 31 . However, dispersion remains a limitation. A soliton-based interferometer has the potential to overcome dispersion, allowing for much longer phase-accumulation times, albeit for an increased quantum noise 32 . To date, only one experiment has demonstrated interferometry with a soliton 8 , in which Bragg pulses were used for splitting and recombination. However, interferom...

We report the preparation of exactly one 87Rb atom and one 133Cs atom in the same optical tweezer as the essential first step towards the construction of a tweezer array of individually trapped 87Rb133Cs molecules. Through careful selection of the tweezer wavelengths, we show how to engineer species-selective trapping potentials suitable for high-fidelity preparation of Rb + Cs atom pairs. Using a wavelength of 814 nm to trap Rb and 938 nm to trap Cs, we achieve loading probabilities of 0.508(6) for Rb and 0.547(6) for Cs using standard red-detuned molasses cooling. Loading the traps sequentially yields exactly one Rb and one Cs atom in 28.4(6)% of experimental runs. Using a combination of an acousto-optic deflector and a piezo-controlled mirror to control the relative position of the tweezers, we merge the two tweezers, retaining the atom pair with a probability of 0.9 9 ( − 0.02 ) ( + 0.01 ) . We use this capability to study hyperfine-state-dependent collisions of Rb and Cs in the combined tweezer and compare the measured two-body loss rates with coupled-channel quantum scattering calculations.