45 research outputs found
A Digital Alkali Spin Maser
Self-oscillating atomic magnetometers, in which the precession of atomic
spins in a magnetic field is driven by resonant modulation, offer high
sensitivity and dynamic range. Phase-coherent feedback from the detected signal
to the applied modulation creates a resonant spin maser system, highly
responsive to changes in the background magnetic field. Here we show a system
in which the phase condition for resonant precession is met by digital signal
processing integrated into the maser feedback loop. This system uses a modest
chip-scale laser and mass-produced dual-pass caesium vapour cell and operates
in a 50 microtesla field, making it a suitable technology for portable
measurements of the geophysical magnetic field. We demonstrate a Cramer-Rao
lower bound-limited resolution of 50 fT at 1 s sampling cadence, and a sensor
bandwidth of 10 kHz. This device also represents an important class of atomic
system in which low-latency digital processing forms an integral part of a
coherently-driven quantum system.Comment: 12 pages, 5 figure
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 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
A feed-forward measurement scheme for periodic noise suppression in atomic magnetometry
We present an unshielded, double-resonance magnetometer in which we have implemented a feed-forward measurement scheme in order to suppress periodic magnetic noise arising from, and correlated with, the mains electricity alternating current line. The technique described here uses a single sensor to track ambient periodic noise and feed forward to suppress it in a subsequent measurement. This feed forward technique has shown significant noise suppression of electrical mains-noise features of up to 22 dB under the fundamental peak at 50 Hz, 3 dB at the first harmonic (100 Hz), and 21 dB at the second harmonic (150 Hz). This technique is software based, requires no additional hardware, and is easy to implement in an existing magnetometer
Grating chips for quantum technologies
We have laser cooled3x10^6 87Rb atoms to 3uK 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
Predatory Organisms with Untapped Biosynthetic Potential:Descriptions of Novel Corallococcus Species C. aberystwythensis sp. nov., C. carmarthensis sp. nov., C. exercitus sp. nov., C. interemptor sp. nov., C. llansteffanensis sp. nov., C. praedator sp. nov., C. sicarius sp. nov., and C. terminator sp. nov
Corallococcus spp. are common soil-dwelling organisms which kill and consume prey microbes through the secretion of antimicrobial substances. Two species of Corallococcus have been described previously (Corallococcus coralloides and Corallococcus exiguus).
A polyphasic approach was taken to characterise antimicrobial, biochemical and phenotypic properties of eight Corallococcus spp. strains and the two type strains. We also report here the genome sequence of the C. exiguus type strain (DSM 14696T).
The genomes of the eight candidate strains, C. exiguus DSM 14696T and C. coralloides DSM 2259T, had an average nucleotide identity below 95% and digital DNA-DNA hybridisation scores less than the 70% lower bound for species identity, indicating they belong to distinct species.
All ten strains, including the two type strains, were thoroughly characterised, including biochemical analysis of their fatty acid methyl esters, substrate utilisation and sugar assimilation. Each strain gave a distinct profile of properties, which together with their genomic differences supports the proposal of the eight candidate strains as novel species: Corallococcus exercitus sp. nov. (AB043AT = DSM 108849T = NBRC 113887T), Corallococcus interemptor sp. nov. (AB047AT = DSM 108843T = NBRC 113888T), Corallococcus aberystwythensis sp. nov. (AB050AT = DSM 108846T = NBRC 114019T), Corallococcus praedator sp. nov. (CA031BT = DSM 108841T = NBRC 113889T), Corallococcus sicarius sp. nov. (CA040BT = DSM 108850T = NBRC 113890T), Corallococcus carmarthenensis sp. nov. (CA043DT = DSM 108842T = NBRC 113891T), Corallococcus llansteffanensis sp. nov. (CA051BT = DSM 108844T = NBRC 114100T) and Corallococcus terminator sp. nov. (CA054AT = DSM 108848T = NBRC 113892T)
Free-induction-decay magnetometer with enhanced optical pumping
Spin preparation prior to a free-induction-decay (FID) measurement can be
adversely affected by transverse bias fields, particularly in the geophysical
field range. A strategy that enhances the spin polarization accumulated before
readout is demonstrated, by synchronizing optical pumping with a magnetic field
pulse that supersedes any transverse fields by over two order of magnitude. The
pulsed magnetic field is generated along the optical pumping axis using a
compact electromagnetic coil pair encompassing a micro-electromechanical
systems (MEMS) vapor cell. The coils also resistively heat the cesium (Cs)
vapor to the optimal atomic density without spurious magnetic field
contributions as they are rapidly demagnetized to approximately zero field
during spin readout. The demagnetization process is analyzed electronically,
and directly with a FID measurement, to confirm that the residual magnetic
field is minimal during detection. The sensitivity performance of this
technique is compared to existing optical pumping modalities across a wide
magnetic field range. A noise floor sensitivity of
was achieved in a field of approximately , in close
agreement with the Cram\'{e}r-Rao lower bound (CRLB) predicted noise density of
.Comment: 10 pages, 7 figure
Three-axis magnetic field detection with a compact, high-bandwidth, single beam zero-field atomic magnetometer
Zero-field optically pumped magnetometers (OPMs) have emerged as an important technology in the realm of biomagnetic research, providing extremely small magnetic field detection capabilities, femtotesla-level, contained in a non-cryogenic compact form factor. Often, compact zero-field OPMs extract single or two-axis magnetic information, typically with a sensing bandwidth of < 100 Hz. The resolution of multiple axes of magnetic field is particularly important for accurate representation of radial components of biomagnetic fields. However, the presence of multi-axis static magnetic fields across the OPM causes measurement errors that degrade signal resolution. 1 Here, we utilise our compact caesium single beam zero-field OPM 2 to address these limitations. We magnetically modulated along both transverse axes of the sensor, at unique frequencies, to extract all axes static-field information. Active feedback can be realised through a lock-in detection scheme at f Mod,x/y for the x- and y-axes, and at 2f Mod,x for the beam axis, z. Operation in this scheme allows for the extraction of three-axis magnetic field information from only a single beam and highlights the importance of active feedback in high-sensitivity biomagnetic applications. The portable sensor also demonstrates a bandwidth with a -3 dB point at ≃ 1600 Hz. The combination of high bandwidth and the capability to extract three-axis magnetic fields opens up exciting prospects for resolving high-frequency biomagnetic signals
Vector magnetometry exploiting phase-geometry effects in a double-resonance alignment magnetometer
Double-resonance optically pumped magnetometers are an attractive instrument for unshielded magnetic-field measurements due to their wide dynamic range and high sensitivity. The use of linearly polarized 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 polarization of transmitted light. We demonstrate experimentally that the amplitude and phase of observed first- and second-harmonic components in the transmitted polarization signal contain sufficient information to measure the 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 an experimentally realized resolution of 1.7 pT and 0.63 mrad in the most sensitive field orientation
Magnetometry optimisation in unshielded environments
Optically pumped magnetometry in unshielded environments is potentially of great advantage in a wide range of surveying and security applications. Optimisation of OPM modulation schemes and feedback in the Mx scheme offers enhanced sensitivity through noise cancellation and decoherence suppression. The work presented demonstrates capability for softwarecontrolled optimisation of OPM performance in ambient fields in the 0.5G range. Effects on magnetometer bandwidth and sensitivity are discussed. Supported by UK National Quantum Technologies Programme
Optical pumping enhancement of a free-induction-decay magnetometer
Spin preparation prior to a free-induction-decay (FID) measurement can be adversely affected by transverse bias fields, particularly in the geophysical field range. A strategy that enhances the spin polarization accumulated before readout is demonstrated, by synchronizing optical pumping with a magnetic field pulse that supersedes any transverse fields by over two order of magnitude. The pulsed magnetic field is generated along the optical pumping axis using a compact electromagnetic coil pair encompassing a micro-electromechanical systems (MEMS) vapor cell. The coils also resistively heat the cesium (Cs) vapor to the optimal atomic density without spurious magnetic field contributions as they are rapidly demagnetized to approximately zero field during spin readout. The demagnetization process is analyzed electronically, and directly with a FID measurement, to confirm that the residual magnetic field is minimal during detection. The sensitivity performance of this technique is compared to existing optical pumping modalities across a wide magnetic field range. A noise floor sensitivity of 238 fT/√Hz was achieved in a field of approximately 50 μT, in close agreement with the Cramér-Rao lower bound (CRLB) predicted noise density of 258 fT/√Hz