Miniaturisation of Quantum Technology: Atomic clocks, grating … · 2020-01-27 · UK Quantum...
Transcript of Miniaturisation of Quantum Technology: Atomic clocks, grating … · 2020-01-27 · UK Quantum...
Miniaturisation of Quantum Technology:Atomic clocks, grating magneto-optical
traps and magnetometry
Erling Riis
University of Strathclyde, Glasgow, UKExperimental Quantum Optics and Photonics Group
http://photonics.phys.strath.ac.uk/
Outline
• (Motivation not required)
• UK landscape
• Grating MOT
• Coherent population trapping for atomic clocks
• Optically pumped atomic magnetometers FPGA
Control
UK Quantum Technology landscape
£350M investment:• 4 QT Hubs - 20 Universities and 170
companies• PhD training • Research Fellowships • Innovate UK joint academic/industry
projects• ~40% to Strathclyde collaborators
£36M MoD programme in QT
£338M of investment proposed for Phase 2 of UK-NQTP.
• Four funded hubs led by:• Birmingham
• Quantum sensors and metrology
• Glasgow• Quantum imaging
• York• Quantum communication
• Oxford• Quantum networks
• NPL closely involved in most
• University of Strathclyde only university taking part in all four
• Led by University of Birmingham
• ~£10M Strathclyde involvement
• Aim: advance cold atom technology for sensors – cf. 20th century electronics revolution
QT Hub for Sensors and Metrology
Our approach to portable atomic clock
• Drop cold atoms• Shielded from environment
• Only weak interatomic interactions
Accuracy
• Favourable scaling for compact clocks:
• Halve interaction time:
Size of trajectory down by factor of four
Linewidth doubles
Data rate doubles } loose 𝟐
Compact measurement device?
• Vision: • Make small (cm-scale) vacuum system with:
• Integrated optics for MOT beams
• Integrated pumping
• Properties:• Large optical access
• Simple single beam alignment
• Micro-fabricated
• Good atom number (~108)
• Low temperature (<10 µK)
©NPL
Opt. Express 17, 13601 (2009)
Mirrors
Opt. Lett. 35, 3453 (2010)
Gratings
Nature Nanotech, 8(5): 323-324,2013
GMOT
Grating chip for cold atom experiments
(3) CSAC performance 3x10-11@100s
(1) Sr lattice 1.6x10-18@5000s
Vo
lum
e
1/(relative instability)
Region of interest
Performance(Allan Deviation)
87Rb88Sr
(2) Atomic fountain
4x10-16 @ 10000s
f0 = 430 THz
Δfa = 1 mHz
Q=4x1017
f0 = 6.8 GHz
Δfa = 10 Hz
Q=6.8x108
N=107
Tc=100 ms
σy (100)=2x10-14(2) T. Heavner et. al. Metrologia 51, 174 (2014)
(3) S. Knappe et. al., Applied Phys. Lett. 85, 1460-1462 (2004)
(1) N Hinkley et. al. Science, 341, 1215-1218 (2013)
Compact measurement device?
Precision measurement – clockLocal Oscillator Counter /
Output
Feedback
Atoms
A microwave clockLocal Oscillator
Feedback
Atoms
The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of caesium 133 atoms (1967)
ȁ1
ȁ2
𝜔0 =𝐸2 − 𝐸1
ℏ
Optical excitation: the basic CPT model
𝜔0 𝛿𝜔
Coherent population trapping: Characteristic reduction in absorption when laser frequency difference δωmatches atomic transition ω0
On resonance: Destructive interference of quantum mechanical amplitudes for light absorption
𝜓 =1
2ȁ1 − ȁ2
-1 0 1
-1 0 1
• Optical pumping poor signal• High contrast schemes:
Lin LinLin || Linσ+/σ—
Push-Pull Optical PumpingPolarization Modulation
The basic CPT model
𝜔0 𝛿𝜔
CPT implementation (87Rb D1)
Raman-Ramsey Technique (Ramsey with a bit of a twist)
Pulse 1 – drives atoms
into a ‘dark’ state:
𝜓 𝑡 =1
2ȁ1 − ȁ2
Pulse 2 – Maps
phase difference
into absorption
1
2ȁ1 − ȁ2
1
2ȁ1 + ȁ2
𝜓 𝑡 =1
2ȁ1 − 𝑒−𝑖 ∆𝐸21𝑡/ℏ ȁ2
Τ∆𝐸21 ℎ =6,834,682,610.904 290 90 𝐻𝑧
During T – evolution:
Ramsey interrogation
∆𝐸21
T
Linewidth: 1/T
Recapture efficiency vs T Atom number vs T and TcModel for equilibrium atom number with recapture from Rakholia et al.
A. V. Rakholia, et al. Phys. Rev. Appl., 2014
𝑁𝑒𝑞 =𝑇𝐿𝑇𝑐
𝑁∞
1 +1 − 𝑟𝛾𝑇𝑐
Atom recapture
• Basic idea: for sufficiently short expansion time atoms remain in the overlap volume and are recaptured readily
Stability optimisation
• Trade-off between drop time and data rate• Increased drop time
Narrower line
Fewer atoms recaptured
Slower data rate
• Estimated realistic limit:
Allan deviation
Assuming, atom shot noise limited detection, TR=10 ms, Tc=100 ms, Nat=107
Clock stability just now
• Currently ~ Τ10−11 𝜏
• Limitations:• Magnetic noise
• Light shifts
• Temperature drifts
• Laser noise
• Doppler shifts
• ….
• Experimental re-build under way
Atomic magnetometry
UnshieldedShielded
• Alkali vapour cells• Optimised geometry & fill• Manufacturable
• Low-noise electronics• VCSEL driver• Polarimeter
• Firmware demodulation• FPGA platform• Additional functionality
Unshielded sensor• 200 µT dynamic range• 1 kHz bandwidth• ~1 pT.Hz-1/2 sensitivity
• 20 ppb @ 50 µT
The Physics
Step 1 Step 2 Step 3
Optical pump
Create an atomic dipole
Monitor precession Initial unpolarised atomic sample
Oscillation frequency in Earth magnetic field ~175 kHz
The journey out of the lab
0.001
0.01
0.1
1
0.1 1 10 100 1000
NEP
(n
T.H
z-1/2
)
Frequency (Hz)
28 mm
On the banks of Loch Lomond
FPGA
Analogue
MEMS vapour cell development• MEMS vapour cell
• Si etched via KOH or DRIE
• Anodically bonded glass/Si/glass
• Cavity contains alkali metal and buffer gas
• Alternative geometries investigated
• Optimisation path for Strathclyde Magnetometry
• Scalable manufacture
• Large and clear optical path
• Controlled/process tuneable buffer gas pressure
• Optional on-board rf/bias coils, heater, cold spot control structures
• Technology development towards
miniaturised magnetometers and
cold atom clocks
– CPT (Raman-Ramsay)
– Microfabricated gratings
• still a lot of work to do with lasers and
vacuum!
– MEMS cell production
– Field-tested magnetometers
Conclusions
Collaborators & Sponsors:
Aidan ArnoldPaul Griffin ER
Jeremy WardGreg HothRachel ElvinMichael WrightBen LewisCarolyn O’DwyerIain Chalmers
Dominic HunterMatt VangeleynChidi NshiiOliver BurrowJames McGilliganStuart InglebyTerry Dyer
Leo Hollberg
http://photonics.phys.strath.ac.uk/
The Team