Stuart InglebyStrathclyde University

Glasgow

Magnetometry Optimisation in Unshielded Environments

IntroductionStrathclydeUniversityQuantumSensors&MetrologyLab-Clocks,MagnetometryandRota?onsensorsMarch2015

25/05/16 Stuart Ingleby DAMOP 2016 2

Introduction•  Unshielded

Magnetometry•  Surveying•  Seismology

•  Performance criteria•  Sensitivity•  Bandwidth•  Portable & scalable•  Arbitrary fields•  Noise rejection

25/05/16 Stuart Ingleby DAMOP 2016 3

Introduction•  Unshielded

Magnetometry•  Surveying•  Seismology

•  Performance criteria•  Sensitivity•  Bandwidth•  Portable & scalable•  Arbitrary fields•  Noise rejection

25/05/16 Stuart Ingleby DAMOP 2016 4

•  Single-laser NMOR•  Software control & feedback•  Iterative optimisation

ADC16-bit

CurrentBuffers

Lock-in

Amp

FrequencyGenera=on

UserInterfaceFiAng

Introduction•  Unshielded

Magnetometry•  Surveying•  Seismology

•  Performance criteria•  Sensitivity•  Bandwidth•  Portable & scalable•  Arbitrary fields•  Noise rejection

25/05/16 Stuart Ingleby DAMOP 2016 5

•  Single-laser NMOR•  Software control & feedback•  Iterative optimisation

ADC16-bit

CurrentBuffers

Lock-in

Amp

FrequencyGenera=on

UserInterfaceFiAng

Cs cell• 28 mm diameter• 2x10-6 torr Cs vapour• Paraffin anti-relaxation• 7 Hz intrinsic relaxation• Made in Fribourg [1]

[1] Castagna, Bison, Di Domenico, Hofer, Knowles, Macchione, Saudan, Weis, Appl. Phys. B 96, 763

NMOR resonance

•  B0 // polarisation•  First-harmonic

response•  BRF modulation•  Software

•  Demodulation•  Phase

correction•  Regression

25/05/16 Stuart Ingleby DAMOP 2016 6

[2] T. Zigdon, A. D. Wilson-Gordon, S. Guttikonda, E. J. Bahr, O. Neitzke, S. M. Rochester, D. Budker, Opt. Express 18, 25494

B0 Orientation & Gradient

•  B0 orientation•  B0 // polarisation

•  Relaxation [3]

25/05/16 Stuart Ingleby DAMOP 2016 7[3]S.Pustelny,D.F.JacksonKimball,S.M.Rochester,V.V.Yashchuk,D.Budker,Phys.Rev.A74,063406

B0 optimisation•  Finite-field

optimisation1  Minimise Bx

By2  Set Bz3  Minimise

HWHM wrt ∇Bx ∇By ∇Bz

•  Convergence 2-3 iterations•  ΔB0 < 20 nT•  ∇Β < 2 nT/mm

25/05/16 Stuart Ingleby DAMOP 2016 8

B0 optimisation•  Finite-field

optimisation1  Minimise Bx

By2  Set Bz3  Minimise

HWHM wrt ∇Bx ∇By ∇Bz

•  Convergence 2-3 iterations•  ΔB0 < 20 nT•  ∇Β < 2 nT/mm

25/05/16 Stuart Ingleby DAMOP 2016 9

B0 optimisation•  Finite-field

optimisation1  Minimise Bx

By2  Set Bz3  Minimise

HWHM wrt ∇Bx ∇By ∇Bz

•  Convergence 2-3 iterations•  ΔB0 < 20 nT•  ∇Β < 2 nT/mm

25/05/16 Stuart Ingleby DAMOP 2016 10

B0 optimisation•  Finite-field

optimisation1  Minimise Bx

By2  Set Bz3  Minimise

HWHM wrt ∇Bx ∇By ∇Bz

•  Convergence 2-3 iterations•  ΔB0 < 20 nT•  ∇Β < 2 nT/mm

25/05/16 Stuart Ingleby DAMOP 2016 11

B0 optimisation•  Finite-field

optimisation1  Minimise Bx

By2  Set Bz3  Minimise

HWHM wrt ∇Bx ∇By ∇Bz

•  Convergence 2-3 iterations•  ΔB0 < 20 nT•  ∇Β < 2 nT/mm

25/05/16 Stuart Ingleby DAMOP 2016 12

B0 optimisation•  Finite-field

optimisation1  Minimise Bx

By2  Set Bz3  Minimise

HWHM wrt ∇Bx ∇By ∇Bz

•  Convergence 2-3 iterations•  ΔB0 < 20 nT•  ∇Β < 2 nT/mm

25/05/16 Stuart Ingleby DAMOP 2016 13

B0 optimisation•  Finite-field

optimisation1  Minimise Bx

By2  Set Bz3  Minimise

HWHM wrt ∇Bx ∇By ∇Bz

•  Convergence 2-3 iterations•  ΔB0 < 20 nT•  ∇Β < 10 nT/mm

25/05/16 Stuart Ingleby DAMOP 2016 14

BRF optimisation•  Signal

•  Saturation

25/05/16 Stuart Ingleby DAMOP 2016 15

Optimised resonance

•  HWHM 680 → 108 Hz (7 Hz intrinsic) • Sensitivity 228 → 20 pT.Hz-1/2

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Stability & Dynamic range

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5 μT

50 μT

•  Dipole ~ 8 mA.m2

•  Location < 5 mm

Response & Noise measurement•  Software PID

feedback•  Self-optimised

•  Phase•  Gain

•  1 Hz field tracking

25/05/16 Stuart Ingleby DAMOP 2016 18

Summary•  QT Hub: application of QT to devices•  Unshielded vapour cell magnetometry•  Scalable, flexible ☞ Hardware < Software•  Arbitrary fields ☞ Studying B0 & ∇B•  Sensitivity ☞ Noise rejection

25/05/16 Stuart Ingleby DAMOP 2016 19

Strathclyde QT Sensors & Metrology HubAidan Arnold, Paul Griffin, Erling RiisYogeshwar Kale, Stuart InglebyVictoria Henderson, Rachel Elvin, James McGilligan