Moving Trap Zeeman
Deceleration of Atoms and
Molecules
Dr David Carty
JQC Launch Event, Newcastle University, June 2013
MMQA - Vision and ambition
• 2011 - Ed Hinds and Mike Tarbutt (Imperial College London), Simon Cornish,
Jeremy Hutson, Eckart Wrede and David Carty (Durham University) won a
£7M, five-year EPSRC programme grant called “MMQA: MicroKelvin
Molecules in a Quantum Array”.
• Quantum simulator - first proposed by Feynman - system of strongly
interacting quantum particles with controllable and tuneable interactions.
“I believe it’s true that with a suitable class of
quantum machines you could imitate any
quantum system, including the physical world.
JQC Launch Event, Newcastle University, June 2013
Slide 1 of 12
MMQA - Vision and ambition
• 2011 - Ed Hinds and Mike Tarbutt (Imperial College London), Simon Cornish,
Jeremy Hutson, Eckart Wrede and David Carty (Durham University) won a
£7M, five-year EPSRC programme grant called “MMQA: MicroKelvin
Molecules in a Quantum Array”.
• Quantum simulator - first proposed by Feynman - system of strongly
interacting quantum particles with controllable and tuneable interactions.
• Strongly interacting quantum systems - challenging to understand, every
particle interacts appreciably with every other, nearly impossible to model with
classical computation.
! Fractional quantum Hall effect.
Ref: Laughlin, Stormer and Tsui, Nobel Prize in Physics 1998 press release
JQC Launch Event, Newcastle University, June 2013
Slide 1 of 12
MMQA - Vision and ambition
• 2011 - Ed Hinds and Mike Tarbutt (Imperial College London), Simon Cornish,
Jeremy Hutson, Eckart Wrede and David Carty (Durham University) won a
£7M, five-year EPSRC programme grant called “MMQA: MicroKelvin
Molecules in a Quantum Array”.
• Quantum simulator - first proposed by Feynman - system of strongly
interacting quantum particles with controllable and tuneable interactions.
• Strongly interacting quantum systems - challenging to understand, every
particle interacts appreciably with every other, nearly impossible to model with
classical computation.
! Fractional quantum Hall effect.
! High-Tc superconductivity.
Ref: http://en.wikipedia.org/wiki/
Superconductor
JQC Launch Event, Newcastle University, June 2013
Ref: Pan et al., Nature, 403, 746 (2000)
Slide 1 of 12
Talk outline
• Quantum simulation with polar molecules.
• One experimental approach within MMQA.
• Moving trap Zeeman deceleration.
• Pulse-width modulation electronics.
• Predicted decelerator performance from Monte-Carlo
trajectory simulations.
• Conclusions and future work.
JQC Launch Event, Newcastle University, June 2013
Slide 2 of 12
Quantum simulation with polar molecules
• Use dipolar molecules - investigate many-body quantum phenomena that
arise when dipolar molecules organise themselves in a trap or lattice.
• Example - molecules in stacked pancake optical traps.
• Self-assembled chains quantum analogues of
classical rheological electro
or magneto-fluids
• Make system rotate - 2D
vortex liquid state with
wavefunction closely
related to that of electrons
in the context of the
fractional quantum Hall
effect.
Ref: D.-W. Wang, M. D. Lukin, and E. Demler, Phys. Rev. Lett. 97, 180413 (2006)
JQC Launch Event, Newcastle University, June 2013
Slide 3 of 12
Quantum simulation with polar molecules
• Use dipolar molecules - investigate many-body quantum phenomena that
arise when dipolar molecules organise themselves in a trap or lattice.
• Example - molecules in an optical lattice. Rich phase diagram.
• Interactions dominate over
tunneling.
• Number squeezing.
• No phase coherence.
• Tunneling dominates over
interactions.
• Poissonian number
distribution.
• Long-range phase coherence.
Ref: K. Góral, L. Santos and M. Lewenstein, Phys. Rev. Lett. 88, 170406 (2002)
JQC Launch Event, Newcastle University, June 2013
Slide 4 of 12
Quantum simulation with polar molecules
• Use dipolar molecules - investigate many-body quantum phenomena that
arise when dipolar molecules organise themselves in a trap or lattice.
• Example - molecules with spin in an optical lattice.
• Lattice spin models - model properties of exotic materials. Systematically
engineer Hamiltonians.
Ref: Micheli et al, Nat. Phys., 2, 341 (2006)
Ha = A
!"
i,j
x
x
z
z
σi+1,j
+ cos θσi,j
σi,j+1
σi,j
#

Hb = A sin θ 
#
σjx σkx +
x links
#
y links

σjy σky  + A cos θ
• Lattice spin models - model properties of exotic materials
JQC Launch Event, Newcastle University, June 2013
Slide 5 of 12
#
z links
σjz σkz
Quantum simulation with polar molecules
• Cannot rely on very weak magnetic dipole interactions to couple spins. Link
electric dipoles to spins.
• Spins couple with much stronger electric interactions.
• Electrically polarise molecules and polarise spins by admixing excited spinrotation states using a microwave field.
Ref: Micheli et al, Nat. Phys., 2, 341 (2006)
Ha = A
!"
i,j
x
x
z
z
σi+1,j
+ cos θσi,j
σi,j+1
σi,j
#

Hb = A sin θ 
#
σjx σkx +
x links
#
y links

σjy σky  + A cos θ
#
z links
• Coupling strength large compared to decoherence rates - robust system.
JQC Launch Event, Newcastle University, June 2013
Slide 5 of 12
σjz σkz
Experimental approach
• Supersonic expansion.
• Or short-pulse buffer-gas
cooled source for slow
(200!m s-1), intense radical
beams, e.g. CaF.
• Some initial laser cooling of
CaF to increase decelerator
loading efficiency.
Ref: Rich Hendricks, ICL, MMQA Annual Meeting talk, Dec. 2011.
JQC Launch Event, Newcastle University, June 2013
Slide 6 of 12
Experimental approach
• Microwave transfer to absolute
ground-state.
• Supersonic expansion.
• Or short-pulse buffer-gas
cooled source for slow
(200!m s-1), intense radical
beams, e.g. CaF.
• Some initial laser cooling of
CaF to increase decelerator
loading efficiency.
• Moving trap Zeeman
decelerator to maximise
number of molecules
brought to standstill.
• Microwave trap for
ground-state molecules.
• Overlap with laser-
cooled atoms –
sympathetic cooling...
• ... and/or laser cooling
if CaF.
JQC Launch Event, Newcastle University, June 2013
Slide 6 of 12
Moving trap Zeeman decelerator
0
√
I0/ 2
molecules
I0
√
I0/ 2
0
√
I0/ 2
v=
I0
√
I0/ 2
32 mm ω
sin α 2π
0
7.7 mm
4.3 mm
Period length =
32 mm
sin α
m
7.7 mm
2.5
α
0.25 mm
m
1.0 mm
• Based on design in Trimeche et al., Eur. Phys. J. D, 65, 263 (2011)
JQC Launch Event, Newcastle University, June 2013
Slide 7 of 12
2.8 mm
Moving trap Zeeman decelerator
Potential in xy-plane
looking down
decelerator.
• I0, dec = 1000 A
1.0 mm
m
m
7.7 mm
0.25 mm
2.5
Longitudinal
potential well
without deceleration.
y
• Iquad = 500 A
x
Cut through
potential along
y-axis at x = 0.
Cut through
potential along x-axis
at y = 0.
JQC Launch Event, Newcastle University, June 2013
Slide 8 of 12
2.8 mm
Moving trap Zeeman decelerator
Longitudinal
potential well
without deceleration.
Potential in xy-plane
looking down
decelerator.
• I0, dec = 1000 A
• Iquad = 500 A
Cut through
potential along
y-axis at x = 0.
Cut through
potential along x-axis
at y = 0.
JQC Launch Event, Newcastle University, June 2013
Slide 8 of 12
Moving trap Zeeman decelerator
Longitudinal
potential well
without deceleration.
Potential in xy-plane
looking down
decelerator.
• I0, dec = 1000 A
• Iquad = 500 A
Cut through
potential along
y-axis at x = 0.
Cut through
potential along x-axis
at y = 0.
• Oscillation of
longitudinal barrier is
small, even for large decelerations.
JQC Launch Event, Newcastle University, June 2013
Slide 8 of 12
Pulse width modulation
H-bridge
• Simplest idea: Use H-bridge and modulate current via
the gate voltage and variable resistance MOSFETs or
IGBTs.
• Problem: R " 0 Ω when on and R " # when off, but
R is finite at all other times. Dissipated power
destroys switch.
IGBTs
Coil
• Pulse width modulation uses switches only in
preferred on/off states.
JQC Launch Event, Newcastle University, June 2013
Slide 9 of 12
Pulse width modulation
H-bridge
• Simplest idea: Use H-bridge and modulate current via
the gate voltage and variable resistance MOSFETs or
IGBTs.
• Problem: R " 0 Ω when on and R " # when off, but
R is finite at all other times. Dissipated power
destroys switch.
s(t) = 2
!
IGBTs
#$
"
t
1
t
with p = (2π × 200 kHz)−1
−
+
p
p 2
off
Coil
on
• Pulse width modulation uses switches only in
preferred on/off states.
• Use sawtooth function to determine length of
current pulses.
• Achieve a sine-wave, but with “noise” at
modulation frequency superimposed.
JQC Launch Event, Newcastle University, June 2013
Slide 9 of 12
Monte Carlo trajectory simulations
• Simulations with Ne(3P2) ~7 u !B-1.
T=5K
T = 500 mK
JQC Launch Event, Newcastle University, June 2013
Slide 10 of 12
Monte Carlo trajectory simulations
• Simulations with Ne(3P2) ~7 u !B-1.
• 2m long decelerator, ~50,000 m s-2 deceleration.
T=5K
T = 500 mK
JQC Launch Event, Newcastle University, June 2013
Slide 10 of 12
Monte Carlo trajectory simulations
• Simulations with Ne(3P2) ~7 u !B-1.
• Decelerator efficiency - 35%
2K
T = 500 mK
JQC Launch Event, Newcastle University, June 2013
Slide 10 of 12
Conclusions
• Introduced the MMQA vision and ambition.
• Arrays of ultracold polar molecules can be used to
model the properties of exotic materials – quantum
simulator.
• Moving trap Zeeman deceleration allied with microwave
trapping of molecules in absolute ground-state followed
by sympathetic cooling or laser cooling (CaF).
• Durham design for moving trap Zeeman decelerator,
magnetic field calculations and trajectory simulations –
efficient trapping of polar molecules.
JQC Launch Event, Newcastle University, June 2013
Slide 11 of 12
Future work
• Actually build decelerator and finish high current electronics.
decelerator with Ne(3P2) atoms before moving on to
• Test and characterise
2
2 +
molecules, i.e. SH( !3/2) and CaF( " ).
• Combine decelerator with microwave trap.
• Overlap microwave trap with magnetically trapped laser cooled atoms for
sympathetic cooling...
• ... and/or laser cool if
molecule is CaF.
• Load ultracold sympathetically cooled molecules into optical lattice.
JQC Launch Event, Newcastle University, June 2013
Slide 12 of 12
Acknowledgements
Wrede Group
Carty Group
• Ulrich Krohn – postdoc
• Arin Mizouri – PhD student
• Undergraduates: K. Horne &
• Dr Eckart Wrede
• Dennis Deng
• Adrian Rowland
• Michelle Lambert
Technical
Advice & support
• Paul White – mechanical workshop
• John Scott – electronics
• Nicolas Vanhaecke (FHI)
• Edvardas Narevicius (Israel)
• Takamasa Momose (UBC)
• Katrin Dulitz (Oxford)
• MMQA team
I.!Dahl-Jorgensen.
Imperial College
London
JQC Launch Event, Newcastle University, June 2013