arXiv subjects

John D. Close

Publications and source records attributed to John D. Close.

17 recordsLinked to original sources

arXiv2026

Atom Interferometry with Transverse Optical Modes

We experimentally demonstrate atom interferometry using the transverse phase profile of an optical mode. As proof-of-principle, we use the helical phase windings of Hypergeometric Gaussian beams for Ramsey interferometry with ensembles of ballistically-expanding cold Rb87 atoms, and we show that the interferometer can measure rotations induced by a motor with a sensitivity that scales linearly with orbital angular momentum and interferometer time. We characterize the thermal decoherence of the interferometer, deriving and experimentally confirming a closed-form expression for the spatially-varying interferometer visibility arising near the singularity of the helical phase winding, motivating the use of condensed atoms in ring-shaped traps.

physics.atom-ph↗

arXiv2025

Tensor gravity gradiometry with a single-axis atom gradiometer

We propose a method for using a single-axis atom interferometric gravity gradiometer to measure off-diagonal elements of the gravity gradient tensor. By tilting the gradiometer, the measured gradient becomes a linear combination of different components of the gravity gradient tensor, and through multiple measurements at different tilts the separate tensor components can be inferred. We present a theoretical and numerical investigation of this technique, both for terrestrial surveys where the tilt is statically set by the user and for surveys where a strapdown sensor is dynamically tilted by the motion of the platform. We show that the gradiometer's sensitivity to the vertical gravity gradient is only slightly reduced by this method while allowing for more gradiometer information to be obtained. Major sources of error and loss of sensitivity on dynamic platforms are shown to be mitigated using an optical-gimbal technique employing commercially-available fibre-optic gyroscopes and tip-tilt mirrors.

physics.atom-ph↗

arXiv2025

Vortex Propagation in Orbital Angular Momentum Beams and the Effects of a Limited Aperture

When generating light with orbital angular momentum by imprinting orbital phase onto a standard Gaussian beam, it is often assumed that the propagation of the generated spatial mode is a Laguerre-Gaussian. However, the true propagation of this beam in a realistic, aperture-limited optical system is non-trivial and has not been thoroughly explored in existing literature. We explore a numerical model that shows the development of an optical vortex mode, propagating from the plane of phase modulation, and the relation of these dynamics to the orbital phase factor $\ell$ and the spatial bandwidth of the optical system. The results of this model are compared to experimental data for beams with $\ell$ values 1, 2, 5, and 10 propagating through a range of spatial filters, with the described model showing agreement in the near field regime.

physics.optics↗

arXiv2025

Multimode feedback cooling of the collective modes of a Bose-Einstein condensate

We experimentally demonstrate cavity-free feedback cooling of the three lowest-lying collective modes of a Bose-Einstein condensate in a prolate harmonic trap. Using shadowgraph imaging as an in situ probe of the atomic density, we measure the time-dependent centers of mass and widths of the condensate in two dimensions and use these measurements to damp oscillations in the two visible dipole modes and the low-frequency quadrupole mode. By inducing oscillations in the condensate, we show that we can efficiently damp the dipole modes to a final mean phonon occupancy per atom of $<1$.

quant-ph↗

arXiv2024

Digital stabilization of an IQ modulator in the carrier suppressed single side-band (CS-SSB) mode for atom interferometry

We present an all-digital method for stabilising the phase biases in an electro-optic I/Q modulator for carrier-suppressed single-sideband modulation. Building on the method presented in S. Wald \ea, Appl. Opt. \textbf{62}, 1-7 (2023), we use the Red Pitaya STEMlab 125-14 platform to digitally generate and demodulate an auxiliary radio-frequency tone whose beat with the optical carrier probes the I/Q modulator's phase imbalances. We implement a multiple-input, multiple-output integral feedback controller which accounts for unavoidable cross-couplings in the phase biases to lock the error signals at exactly zero where optical power fluctuations have no impact on phase stability. We demonstrate $>23\,\rm dB$ suppression of the optical carrier relative to the desired sideband at $+3.4\,\rm GHz$ over a period of $15$ hours and over temperature variations of $20^\circ\rm C$.

physics.optics↗

arXiv2024

Optimal strategies for low-noise detection of atoms using resonant frequency modulation spectroscopy in cold atom interferometers

Resonant frequency modulation spectroscopy has been previously used as a highly-sensitive method for measuring the output of cold atom interferometers. Using a detailed model that accounts for optical saturation, laser intensities and atomic densities that vary spatially, and radiation pressure on the atoms, we theoretically investigate under what parameter regimes the optimum signal-to-noise ratio is found under experimentally realistic conditions. We compare this technique to the standard method of fluorescence imaging and find that it outperforms fluorescence imaging for compact interferometers using condensed atomic sources or where the photon collection efficiency is limited. However, we find that fluorescence imaging is likely to be the preferred method when using squeezed atomic sources due to limited atom number.

physics.atom-ph↗

arXiv2024

Dual Open Atom Interferometry for Compact and Mobile Quantum Sensing

We demonstrate an atom interferometer measurement protocol compatible with operation on a dynamic platform. Our method employs two open interferometers, derived from the same atomic source, with different interrogation times to eliminate initial velocity dependence while retaining precision, accuracy, and long term stability. We validate the protocol by measuring gravitational tides, achieving a precision of 4.5 {\mu}Gal in 2000 runs (6.7 h), marking the first demonstration of inertial quantity measurement with open atom interferometry that achieves long-term phase stability.

quant-ph↗

arXiv2020

High Precision, Quantum-Enhanced Gravimetry with a Bose-Einstein Condensate

We show that the inherently large interatomic interactions of a Bose-Einstein condensate (BEC) can enhance the sensitivity of a high precision cold-atom gravimeter beyond the shot-noise limit (SNL). Through detailed numerical simulation, we demonstrate that our scheme produces spin-squeezed states with variances up to 14 dB below the SNL, and that absolute gravimetry measurement sensitivities between 2 and 5 times below the SNL are achievable with BECs between $10^4$ and $10^6$ in atom number. Our scheme is robust to phase diffusion, imperfect atom counting, and shot-to-shot variations in atom number and laser intensity. Our proposal is immediately achievable in current laboratories, since it needs only a small modification to existing state-of-the-art experiments and does not require additional guiding potentials or optical cavities.

quant-ph↗

arXiv2016

Non-destructive shadowgraph imaging of ultracold atoms

An imaging system is presented that is capable of far-detuned non-destructive imaging of a Bose-Einstein condensate with the signal proportional to the second spatial derivative of the density. Whilst demonstrated with application to $^{85}\text{Rb}$, the technique generalizes to other atomic species and is shown to be capable of a signal to noise of ${\sim}25$ at $1$GHz detuning with $100$ in-trap images showing no observable heating or atom loss. The technique is also applied to the observation of individual trajectories of stochastic dynamics inaccessible to single shot imaging. Coupled with a fast optical phase lock loop, the system is capable of dynamically switching to resonant absorption imaging during the experiment.

physics.atom-ph↗

arXiv2016

A quantum sensor: simultaneous precision gravimetry and magnetic gradiometry with a Bose-Einstein condensate

A Bose-Einstein condensate is used as an atomic source for a high precision sensor. A $5\times 10^6$ atom F=1 spinor condensate of $^{87}$Rb is released into free fall for up to $750$ms and probed with a Mach-Zehnder atom interferometer based on Bragg transitions. The Bragg interferometer simultaneously addresses the three magnetic states, $\left| m_f=1,0,-1 \right\rangle$, facilitating a simultaneous measurement of the acceleration due to gravity with an asymptotic precision of $2.1\times 10^{-9}$$Δ$g/g and the magnetic field gradient to a precision $8$pT/m.

physics.atom-ph↗

arXiv2015

Observation of Breathers in an Attractive Bose Gas

In weakly nonlinear dispersive systems, solitons are spatially localized solutions which propagate without changing shape through a delicate balance between dispersion and self-focusing nonlinear effects. These states have been extensively studied in Bose-Einstein condensates, where interatomic interactions give rise to such nonlinearities. Previous experimental work with matter wave solitons has been limited to static intensity profiles. The creation of matter wave breathers--dispersionless soliton-like states with collective oscillation frequencies driven by attractive mean-field interactions--have been of theoretical interest due to the exotic behaviour of interacting matter wave systems. Here, using an attractively interacting Bose-Einstein condensate, we present the first observation of matter wave breathers. A comparison between experimental data and a cubic-quintic Gross-Pitaevskii equation suggests that previously unobserved three-body interactions may play an important role in this system. The observation of long lived stable breathers in an attractively interacting matter wave system indicates that there is a wide range of previously unobserved, but theoretically predicted, effects that are now experimentally accessible.

cond-mat.quant-gas↗

arXiv2014

A Bright Solitonic Matter-Wave Interferometer

We present the first realisation of a solitonic atom interferometer. A Bose-Einstein condensate of $1\times10^4$ atoms of rubidium-85 is loaded into a horizontal optical waveguide. Through the use of a Feshbach resonance, the $s$-wave scattering length of the $^{85}$Rb atoms is tuned to a small negative value. This attractive atomic interaction then balances the inherent matter-wave dispersion, creating a bright solitonic matter wave. A Mach-Zehnder interferometer is constructed by driving Bragg transitions with the use of an optical lattice co-linear with the waveguide. Matter wave propagation and interferometric fringe visibility are compared across a range of $s$-wave scattering values including repulsive, attractive and non-interacting values. The solitonic matter wave is found to significantly increase fringe visibility even compared with a non-interacting cloud.

quant-ph↗

arXiv2014

A faster scaling in acceleration-sensitive atom interferometers

Atom interferometers have been used to measure acceleration with at best a $T^2$ scaling in sensitivity as the interferometer time $T$ is increased. This limits the sensitivity to acceleration which is theoretically achievable by these configurations for a given frequency of acceleration. We predict and experimentally measure the acceleration-sensitive phase shift of a large-momentum-transfer atom interferometer based upon Bloch oscillations. Using this novel interferometric scheme we demonstrate an improved scaling of sensitivity which will scale as $T^3$. This enhanced scaling will allow an increase in achievable sensitivity for any given frequency of an oscillatory acceleration signal, which will be of particular use for inertial and navigational sensors, and proposed gravitational wave detectors. A straight forward extension should allow a $T^4$ scaling in acceleration sensitivity.

cond-mat.quant-gas↗

arXiv2013

The Role of Source Coherence in Atom Interferometery

The role of source cloud spatial coherence in a Mach-Zehnder type atom interferometer is experimentally investigated. The visibility and contrast of a Bose-Einstein condensate (BEC) and three thermal sources with varying spatial coherence are compared as a function of interferometer time. At short times, the fringe visibility of a BEC source approaches 100 % nearly independent of pi pulse efficiency, while thermal sources have fringe visibilities limited to the mirror efficiency. More importantly for precision measurement systems, the BEC source maintains interference at interferometer times significantly beyond the thermal source.

physics.atom-ph↗

arXiv2013

80hk Momentum Separation with Bloch Oscillations in an Optically Guided Atom Interferometer

We demonstrate phase sensitivity in a horizontally guided, acceleration-sensitive atom interferometer with a momentum separation of 80hk between its arms. A fringe visibility of 7% is observed. Our coherent pulse sequence accelerates the cold cloud in an optical waveguide, an inherently scalable route to large momentum separation and high sensitivity. We maintain coherence at high momentum separation due to both the transverse confinement provided by the guide, and our use of optical delta-kick cooling on our cold-atom cloud. We also construct a horizontal interferometric gradiometer to measure the longitudinal curvature of our optical waveguide.

cond-mat.quant-gas↗

arXiv2011

Why momentum width matters for atom interferometry with Bragg pulses

We theoretically consider the effect of the atomic source's momentum width on the efficiency of Bragg mirrors and beamsplitters and, more generally, on the phase sensitivity of Bragg pulse atom interferometers. By numerical optimization, we show that an atomic cloud's momentum width places a fundamental upper bound on the maximum transfer efficiency of a Bragg mirror pulse, and furthermore limits the phase sensitivity of a Bragg pulse atom interferometer. We quantify these momentum width effects, and precisely compute how mirror efficiencies and interferometer phase sensitivities vary as functions of Bragg order and source type. Our results and methodology allow for an efficient optimization of Bragg pulses and the comparison of different atomic sources, and will help in the design of large momentum transfer Bragg mirrors and beamsplitters for use in atom-based inertial sensors.

quant-ph↗

arXiv2004

Pump-probe differencing technique for cavity-enhanced, noise-canceling saturation laser spectroscopy

We present an experimental technique enabling mechanical-noise free, cavity-enhanced frequency measurements of an atomic transition and its hyperfine structure. We employ the 532nm frequency doubled output from a Nd:YAG laser and an iodine vapour cell. The cell is placed in a traveling-wave Fabry-Perot interferometer (FPI) with counter-propagating pump and probe beams. The FPI is locked using the Pound-Drever-Hall (PDH) technique. Mechanical noise is rejected by differencing pump and probe signals. In addition, this differenced error signal gives a sensitive measure of differential non-linearity within the FPI.

physics.optics↗