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We demonstrate the integration of micro-electro-mechanical-systems (MEMS) scanning mirrors as active elements for the local optical pumping of ultra-cold atoms in a magneto-optical trap. A pair of MEMS mirrors steer a focused resonant beam through a cloud of trapped atoms shelved in the \textit{F}=1 ground-state of \textsuperscript{87}Rb for spatially-selective fluorescence of the atom cloud. Two-dimensional control is demonstrated by forming geometrical patterns along the imaging axis of the cold atom ensemble. Such control of the atomic ensemble with a microfabricated mirror pair could find applications in single atom selection, local optical pumping and arbitrary cloud shaping. This approach has significant potential for miniaturisation and in creating portable control systems for quantum optic experiments., 4 pages, 3 figures

Cold atom fountain clocks provide exceptional long term stability as they increase interrogation time at the expense of a larger size. We present a compact cold atom fountain using a grating magneto-optical trap (GMOT) to laser cool and launch the atoms in a simplified optical setup. The fountain is evaluated using coherent population trapping and demonstrates improved single-shot stability from the launch. Ramsey times up to 100 ms were measured with a corresponding fringe linewidth of 5 Hz. This technique could improve both short- and long-term stability of cold atom clocks whilst remaining compact for portable applications., 5 pages, 4 figures

Compact vacuum systems are key enabling components for cold atom technologies, facilitating extremely accurate sensing applications. There has been important progress towards a truly portable compact vacuum system, however size, weight and power consumption can be prohibitively large, optical access may be limited, and active pumping is often required. Here, we present a centilitre-scale ceramic vacuum chamber with He-impermeable viewports and an integrated diffractive optic, enabling robust laser cooling with light from a single polarization-maintaining fibre. A cold atom demonstrator based on the vacuum cell delivers $10^7$ laser-cooled $^{87}$Rb atoms per second, using minimal electrical power. With continuous Rb gas emission active pumping yields a $10^{-7}\,$mbar equilibrium pressure, and passive pumping stabilises to $3\times 10^{-6}\,$mbar, with a $17\,$day time constant. A vacuum cell, with no Rb dispensing and only passive pumping, has currently kept a similar pressure for more than \ch{500 days}. The passive-pumping vacuum lifetime is several years, estimated from short-term He throughput, with many foreseeable improvements. This technology enables wide-ranging mobilization of ultracold quantum metrology., 6 pages, 2 figures, to appear in Applied Physics Letters

We demonstrate a simple stacked scheme that enables absorption imaging through a hole in the surface of a grating magneto-optical trap (GMOT) chip, placed immediately below a micro-fabricated vacuum cell. The imaging scheme is capable of overcoming the reduced optical access and surface scatter that is associated with this chip-scale platform, while further permitting both trapping and imaging of the atoms from a single incident laser beam. The through-hole imaging is used to characterise the impact of the reduced optical overlap volume of the GMOT in the chip-scale cell, with an outlook to an optimised atom number in low volume systems., 5 pages, 3 figures

Chip-scale atomic devices built around micro-fabricated alkali vapor cells are at the forefront of compact metrology and atomic sensors. We demonstrate a micro-fabricated vapor cell that is actively-pumped to ultra-high-vacuum (UHV) to achieve laser cooling. A grating magneto optical trap (GMOT) is incorporated with the 4 mm-thick Si/glass vacuum cell to demonstrate the feasibility of a fully-miniaturized laser cooling platform. A two-step optical excitation process in rubidium is used to overcome surface-scatter limitations to the GMOT imaging. The unambiguous miniaturization and form-customizability made available with micro-fabricated UHV cells provide a promising platform for future compact cold-atom sensors., Comment: 5 pages, 3 figures

Studying the conversion between transverse light modes via four-wave mixing in a heated rubidium vapour, we demonstrate and explain a transfer between azimuthal and radial mode numbers. These relate to orthogonal modal dimensions, which one would not normally expect to interact. While angular momentum conservation in this nonlinear process dictates the selection rules for the angular mode number, the role of the radial mode number is more esoteric. We demonstrate systematically that the Gouy phase is the key to understanding this conversion, leading to strikingly different conversion behaviour in the thick and thin medium regime. Our experimental investigation of the transition between these regimes bridges the gap between previous experiments in atomic thick media and work in nonlinear crystals. Our work sets a clear starting point to explore new territory in the thick medium regime, allowing efficient radial-to-azimuthal and radial-to-radial mode conversion., 6 pages, 5 figures, Supplementary Material - 4 pages. Thanks to the referees for their comments

We optically assess Fresnel zone plates (FZPs) that are designed to guide cold atoms. Imaging of various ring patterns produced by the FZPs gives an average RMS error in the brightest part of the ring of 3% with respect to trap depth. This residue will be due to the imaging system, incident beam shape and FZP manufacturing tolerances. Axial propagation of the potentials is presented experimentally and through numerical simulations, illustrating prospects for atom guiding without requiring light sheets., Comment: 10 pages, 5 figures

Clocks based on cold atoms offer unbeatable accuracy and long-term stability, but their use in portable quantum technologies is hampered by a large physical footprint. Here, we use the compact optical layout of a grating magneto-optical trap (gMOT) for a precise frequency reference. The gMOT collects $10^7$ $^{87}$Rb atoms, which are subsequently cooled to $20\,\mu$K in optical molasses. We optically probe the microwave atomic ground-state splitting using lin$\perp$lin polarised coherent population trapping and a Raman-Ramsey sequence. With ballistic drop distances of only $0.5\,$mm, the measured short-term fractional frequency stability is $2 \times 10 ^{-11} /\sqrt{\tau}$., Comment: 8 pages, 4 figures

Double-resonance optically pumped magnetometers are an attractive instrument for unshielded magnetic field measurements due to their wide dynamic range and high sensitivity. Use of linearly polarised pump light creates alignment in the atomic sample, which evolves in the local static magnetic field, and is driven by a resonant applied field perturbation, modulating the polarisation of transmitted light. We show for the first time that the amplitude and phase of observed first- and second-harmonic components in the transmitted polarisation signal contain sufficient information to measure static magnetic field magnitude and orientation. We describe a laboratory system for experimental measurements of these effects and verify a theoretical derivation of the observed signal. We demonstrate vector field tracking under varying static field orientations and show that the static field magnitude and orientation may be observed simultaneously, with experimentally realised resolution of 1.7 pT and 0.63 mrad in the most sensitive field orientation., Comment: 8 pages, 7 figures

An atom interferometer using a Bose-Einstein condensate of $^{87}$Rb atoms is utilized for the measurement of magnetic field gradients. Composite optical pulses are used to construct a spatially symmetric Mach-Zehnder geometry. Using a biased interferometer we demonstrate the ability to measure small residual forces in our system at the position of the atoms. These are a residual magnetic field gradient of 15$\pm$2 mG/cm and and an inertial acceleration of 0.08$\pm$0.02 m/s$^2$. Our method has important applications in the calibration of precision measurement devices and the reduction of systematic errors., 7 pages, 6 figures

Optically pumped atomic magnetometers (OPMs) offer highly sensitive magnetic measurements using compact hardware, offering new possibilities for practical precision sensors. Double-resonance OPM operation is well suited to unshielded magnetometry, due to high sensor dynamic range. However, sensor response is highly anisotropic with variation in the orientation of the magnetic field. We present data quantifying these effects and discuss implications for the design of practical sensors., IEEE Sensors 2017 paper preprint

Double resonance optically pumped magnetometry can be used to measure static magnetic fields with high sensitivity by detecting a resonant atomic spin response to a small oscillating field perturbation. Determination of the resonant frequency yields a scalar measurement of static field ($B_0$) magnitude. We present calculations and experimental data showing that the on-resonance polarimeter signal of light transmitted through an atomic vapour in arbitrarily oriented $B_0$ may be modelled by considering the evolution of alignment terms in atomic polarisation. We observe that the amplitude and phase of the magnetometer signal are highly dependent upon $B_0$ orientation, and present precise measurements of the distribution of these parameters over the full 4{\pi} solid angle.

An integrated system of hardware and software allowing precise definition of arbitrarily oriented magnetic fields up to |B| = 1 {\mu}T within a five-layer mumetal shield is described. The system is calibrated with reference to magnetic resonance observed between Zeeman states of the 6S$_{1/2}$ F = 4 $^{133}$Cs ground state. Magnetic field definition over the full 4{\pi} solid angle is demonstrated, with one-sigma tolerances in magnitude, orientation and gradient of {\delta}|B| = 0.94 nT, {\delta}{\theta} = 5.9 mrad and {\delta}$\nabla$ B = 13.0 pT/mm, respectively. This field control is used to empirically map Mx magnetometer signal amplitude as a function of the static field (B0) orientation., Comment: 14 pages, 10 figures

We have laser cooled 3$\times10^6$ $^{87}$Rb atoms to 3$\mu$K in a micro-fabricated grating magneto-optical trap (GMOT), enabling future mass-deployment in highly accurate compact quantum sensors. We magnetically trap the atoms, and use Larmor spin precession for magnetic sensing in the vicinity of the atomic sample. Finally, we demonstrate an array of magneto-optical traps with a single laser beam, which will be utilised for future cold atom gradiometry., Comment: 8 pages, 6 figures

Laser cooled atoms are central to modern precision measurements. They are also increasingly important as an enabling technology for experimental cavity quantum electrodynamics, quantum information processing and matter wave interferometry. Although significant progress has been made in miniaturising atomic metrological devices, these are limited in accuracy by their use of hot atomic ensembles and buffer gases. Advances have also been made in producing portable apparatus that benefit from the advantages of atoms in the microKelvin regime. However, simplifying atomic cooling and loading using microfabrication technology has proved difficult. In this letter we address this problem, realising an atom chip that enables the integration of laser cooling and trapping into a compact apparatus. Our source delivers ten thousand times more atoms than previous magneto-optical traps with microfabricated optics and, for the first time, can reach sub-Doppler temperatures. Moreover, the same chip design offers a simple way to form stable optical lattices. These features, combined with the simplicity of fabrication and the ease of operation, make these new traps a key advance in the development of cold-atom technology for high-accuracy, portable measurement devices., Comment: 5 pages, 5 figures

We have simulated the optical properties of micro-fabricated Fresnel zone plates (FZPs) as an alternative to spatial light modulators (SLMs) for producing non-trivial light potentials to trap atoms within a lensless Fresnel arrangement. We show that binary (1-bit) FZPs with wavelength (1 \mu m) spatial resolution consistently outperform kinoforms of spatial and phase resolution comparable to commercial SLMs in root mean square error comparisons, with FZP kinoforms demonstrating increasing improvement for complex target intensity distributions. Moreover, as sub-wavelength resolution microfabrication is possible, FZPs provide an exciting possibility for the creation of static cold-atom trapping potentials useful to atomtronics, interferometry, and the study of fundamental physics., Comment: 14 pages, to appear in New Journal of Physics Atomtronics special issue

We have studied the optical properties of gratings micro-fabricated into semiconductor wafers, which can be used for simplifying cold-atom experiments. The study entailed characterisation of diffraction efficiency as a function of coating, periodicity, duty cycle and geometry using over 100 distinct gratings. The critical parameters of experimental use, such as diffraction angle and wavelength are also discussed, with an outlook to achieving optimal ultracold experimental conditions., 8 pages

We present experimental observations of coherent spin-population oscillations in a cold thermal, Bose gas of spin-1 sodium-23 atoms. The population oscillations in a multi-spatial-mode thermal gas have the same behavior as those observed in a single-spatial-mode antiferromagnetic spinor Bose Einstein condensate. We demonstrate this by showing that the two situations are described by the same dynamical equations, with a factor of two change in the spin-dependent interaction coefficient, which results from the change to particles with distinguishable momentum states in the thermal gas. We compare this theory to the measured spin population evolution after times up to a few hundreds of ms, finding quantitative agreement with the amplitude and period. We also measure the damping time of the oscillations as a function of magnetic field., Comment: 5 pages, 3 figures

We report the first demonstration of an inductively coupled magnetic ring trap for cold atoms. A uniform, ac magnetic field is used to induce current in a copper ring, which creates an opposing magnetic field that is time-averaged to produce a smooth cylindrically symmetric ring trap of radius 5 mm. We use a laser-cooled atomic sample to characterise the loading efficiency and adiabaticity of the magnetic potential, achieving a vacuum-limited lifetime in the trap. This technique is suitable for creating scalable toroidal waveguides for applications in matterwave interferometry, offering long interaction times and large enclosed areas., Comment: 12 pages, 6 figures

A planar triplet of diffraction gratings is used to transform a single laser beam into a four-beam tetrahedral magneto-optical trap. This `flat' pyramid diffractor geometry is ideal for future microfabrication. We demonstrate the technique by trapping and subsequently sub-Doppler cooling 87Rb atoms to 30microKelvin., Comment: 3 pages, 4 figures

We present a viewport for use in ultrahigh vacuum (UHV) based upon the preflattened solder seal design presented in earlier work [Cox et al., Rev. Sci. Instrum. 74, 3185 (2003)]. The design features significant modifications to improve long term performance. The windows have been leak tested to less than 10(-10) atm cm(3)/s. From atom number measurements in an optical dipole trap loaded from a vapor cell magneto-optical trap inside a vacuum chamber accommodating these viewports, we measure a trap lifetime of 9.5 s suggesting a pressure of around 10(-10) Torr limited by background rubidium vapor pressure. We also present a simplified design where the UHV seal is made directly to a vacuum pipe.

We propose and numerically investigate a scalable ring trap for cold atoms that surmounts problems of roughness of the potential and end--effects of trap wires. A stable trapping potential is formed about an electrically isolated, conducting loop in an ac magnetic field by time averaging the superposition of the external and induced magnetic fields. We investigate the use of additional fields to eliminate Majorana spin flip losses and to create novel trapping geometries. The possibility of micro--fabrication of these ring traps offers the prospect of developing Sagnac atom interferometry in atom--chip devices., Comment: 4 pages, 5 figures

We have used diffraction gratings to simplify the fabrication, and dramatically increase the atomic collection efficiency, of magneto-optical traps using micro-fabricated optics. The atom number enhancement was mainly due to the increased beam capture volume, afforded by the large area (4cm^2) shallow etch (200nm) binary grating chips. Here we provide a detailed theoretical and experimental investigation of the on-chip magneto-optical trap temperature and density in four different chip geometries using 87Rb, whilst studying effects due to MOT radiation pressure imbalance. With optimal initial MOTs on two of the chips we obtain both large atom number (2x10^7) _and_ sub-Doppler temperatures (50uK) after optical molasses., 12 pages, 6 figures, 2 linked supplementary figures

We report on a method of light-shift engineering where an auxiliary laser is used to tune the atomic transition frequency. The technique is used to selectively load a specific region of an optical lattice. The results are explained by calculating the differential light-shift of each hyperfine state. We conclude that the remarkable spatial selectivity of light-shift engineering using an auxiliary laser provides a powerful technique to prepare ultra-cold trapped atoms for experiments on quantum gases and quantum information processing., 4 pages, 5 figures

We have realised a 4-beam pyramidal magneto-optical trap ideally suited for future microfabrication. Three mirrors split and steer a single incoming beam into a tripod of reflected beams, allowing trapping in the four-beam overlap volume. We discuss the influence of mirror angle on cooling and trapping, finding optimum efficiency in a tetrahedral configuration. We demonstrate the technique using an ex-vacuo mirror system to illustrate the previously inaccessible supra-plane pyramid MOT configuration. Unlike standard pyramidal MOTs both the pyramid apex and its mirror angle are non-critical and our MOT offers improved molasses free from atomic shadows in the laser beams. The MOT scheme naturally extends to a 2-beam refractive version with high optical access. For quantum gas experiments, the mirror system could also be used for a stable 3D tetrahedral optical lattice., 8 pages, 6 figures, 2 movies