arXiv subjects

Aidan S. Arnold

Publications and source records attributed to Aidan S. Arnold.

31 records · Page 2Linked to original sources

arXiv2017

Optically Pumped Magnetometry in Arbitrarily Oriented Magnetic Fields

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.

physics.atom-ph↗

arXiv2017

Orientational Effects on the Amplitude and Phase of Polarimeter Signals in Double Resonance Atomic Magnetometry

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 4π solid angle.

physics.atom-ph↗

arXiv2017

Grating chips for quantum technologies

We have laser cooled 3$\times10^6$ $^{87}$Rb atoms to 3$μ$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.

physics.atom-ph↗

arXiv2016

Cavity-enhanced frequency up-conversion in rubidium vapour

We report the first use of a ring cavity to both enhance the output power and dramatically narrow the linewidth ($<1\,$MHz) of blue light generated by four wave mixing in a rubidium vapour cell. We find that the high output power available in our cavity-free system leads to power broadening of the generated blue light linewidth. Our ring cavity removes this limitation, allowing high output power and narrow linewidth to be achieved concurrently. As the cavity blue light is widely tunable over the $^{85}$Rb 5S$_{1/2} \,\,F=3$ $\rightarrow$ 6P$_{3/2}$ transition, this narrow linewidth light would be suitable for second-stage laser cooling, which could be valuable for efficient $^{85}$Rb BEC production.

physics.atom-ph↗

arXiv2016

Diffraction grating characterisation for cold-atom experiments

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.

physics.atom-ph↗

arXiv2015

Phase-space properties of magneto-optical traps utilising micro-fabricated gratings

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.

physics.atom-ph↗

arXiv2014

Inductive dressed ring traps for ultracold atoms

We present two novel dressed inductive ring trap geometries, ideal for atom interferometry or studies of superfluidity and well-suited to utilisation in atom chip architectures. The design permits ring radii currently only accessible via near-diffraction-limited optical traps, whilst retaining the ultra-smooth magnetic potential afforded by inductive traps. One geometry offers simple parallel implementation of multiple rings, whereas the other geometry permits axial beam-splitting of the torus suitable for whole-ring atom interferometry.

physics.atom-ph↗

arXiv2014

Inductively guided circuits for ultracold dressed atoms

We propose a flexible and robust scheme to create closed quasi-one dimensional guides for ultra-cold atoms through the dressing of hyperfine sub-levels of the atomic ground state. The dressing field is spatially modulated by inductive effects over a micro-engineered conducting loop, freeing the trapping region from leading wires in its proximity. We show that arrays of connected ring traps can also be created by carefully designing the shape of the conducting loop. We report on characteristics of the trap and mechanisms that limit the range of parameters available for experimental implementation, including non-adiabatic losses and heat dissipation by induced currents. We outline conditions to select appropriate parameters for operation of the trap with atom-chip technology.

physics.atom-ph↗

arXiv2013

Optomechanical self-structuring in cold atomic gases

The rapidly developing field of optomechanics aims at the combined control of optical and mechanical (solid-state or atomic) modes. In particular, laser cooled atoms have been used to exploit optomechanical coupling for self-organization in a variety of schemes where the accessible length scales are constrained by a combination of pump modes and those associated to a second imposed axis, typically a cavity axis. Here, we consider a system with many spatial degrees of freedom around a single distinguished axis, in which two symmetries - rotations and translations in the plane orthogonal to the pump axis - are spontaneously broken. We observe the simultaneous spatial structuring of the density of a cold atomic cloud and an optical pump beam. The resulting patterns have hexagonal symmetry. The experiment demonstrates the manipulation of matter by opto-mechanical self-assembly with adjustable length scales and can be potentially extended to quantum degenerate gases.

physics.atom-ph↗

arXiv2012

Extending dark optical trapping geometries

New counter-propagating geometries are presented for localising ultracold atoms in the dark regions created by the interference of Laguerre-Gaussian laser beams. In particular dark helices, an 'optical revolver,' axial lattices of rings and axial lattices of ring lattices of rings are considered and a realistic scheme for achieving phase-stability is explored. The dark nature of these traps will enable their use as versatile tools for low-decoherence atom interferometry with zero differential light shifts.

physics.atom-ph↗

arXiv2010

Laser cooling with a single laser beam and a planar diffractor

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.

physics.atom-ph↗

arXiv2009

Single-laser, one beam, tetrahedral magneto-optical trap

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.

physics.atom-ph↗

arXiv2008

Experimental single-impulse magnetic focusing of launched cold atoms

Single-impulse three-dimensional magnetic focusing of vertically launched cold atoms has been observed. Four different configurations of the lens were used to vary the relative radial and axial focusing properties. Compact focused clouds of 85Rb were seen for all four configurations. It is shown that an atom-optical ray matrix approach for describing the lensing action is insufficient. Numerical simulation using a full approximation to the lens's magnetic field shows very good agreement with the radial focusing properties of the lens. However, the axial (vertical direction) focusing properties are less well described and the reasons for this are discussed.

physics.atom-ph↗