collisions in ultracold metastable helium gases
DESCRIPTION
G. B. Partridge , J.-C. Jaskula, M. Bonneau, D. Boiron, C. I. Westbrook Laboratoire Charles Fabry de l’Institut d’Optique, Palaiseau France. COLLISIONS IN ULTRACOLD METASTABLE HELIUM GASES. Methods, apparatus, He*. Experiments: 4-wave mixing of matter waves. Outline. - PowerPoint PPT PresentationTRANSCRIPT
COLLISIONS IN ULTRACOLD COLLISIONS IN ULTRACOLD METASTABLE HELIUM GASESMETASTABLE HELIUM GASES
G. B. Partridge, J.-C. Jaskula, M. Bonneau, D. Boiron, C. I. WestbrookLaboratoire Charles Fabry de l’Institut d’Optique, Palaiseau France
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OutlineOutline
Methods, apparatus, He*.
Motivation and Background--Optics, atomoptics, quantum optics, quantum atom optics… Optics, atomoptics, quantum optics, quantum atom optics…
Optical Trapping Optical Trapping andand Relative Number Relative Number
SqueezingSqueezing
Experiments:
4-wave mixing of matter 4-wave mixing of matter waveswaves
Spin MixturesSpin Mixtures
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Motivation, atom optics…Motivation, atom optics…
Optics : Photons, waves… wave particle duality.
Atomic physics atom optics :i.e – slits, interferrometers, etc
Bec coherent atom optics:Atom Laser, fringes, + nonlinear atom
optics (interactions): 4wm , solitons…
Quantum atom optics? -ex’s correlations, squeezing,
entanglement, teleportation…
Use counting, single particles, statistics…--Key is detection: metastable Helium
(He*).
T. Pfau (Stuttgart)
L. Deng et al. (NIST)
Strecker et al. (Rice)
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He* : What’s it hiding?He* : What’s it hiding?
The 23S1 state of He has a decay time ~ 8000 s !*
*single atom ~ spin polarized
This energy can kick off electrons & ionize atoms of surfaces that the atom meets.
The stored energy of the metastable state is 19.8 eV/atom.
Add in a potential, get an avalanche of electrons.
High gain amplifier = single atom sensitivity.
e-
+
(So what?)
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Trapping and Cooling He*Trapping and Cooling He*
Laser cooling helium?
Behaves a lot like an alkali-metal.
(Cycling Optical Transition, magnetically trappable )
I
I
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Single Atom DetectionSingle Atom Detection
Use a micro-channel plate (many e- avalanche detectors in parallel) to give position information.
Gather resulting electric pulses using crossed delay lines.
Use relative arrival times to reconstruct atoms’ positions
(time of flight) in 3D.
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A new tool for He*A new tool for He*
Statistical measurements: 1000’s of repetitions.
magnetic trap was not engineered for this…
(although we try anyway)Long term: favors Optical Trap
magnetic optical
TOF
Also, better geometry: aligns long axis of potential ( short TOF, short
correlation length) w/ high resolution direction, Z.
Gives freedom to try spin mixtures…
First step towards more complicated potentials for He*
(lattices, disorder etc.)
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BEC of He* in the optical BEC of He* in the optical traptrap
N0 = 105 r = 1.5 kHz, z = 8 Hz
Transfer from magnetic trap after some pre-cooling: N = 5 x 106, T = 15 K
Evaporate by reducing intensity of trap laser over ~ 4 sec.
G. B. Partridge, J.-C. Jaskula, M. Bonneau, D. Boiron, C. I. Westbrook, Phys. Rev. A 81, 053631 (2010).
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Quantum Optics: photon Quantum Optics: photon pairspairs
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Matter Wave FWM: atom Matter Wave FWM: atom pairspairs
S-wave interactions lead to spherical shell of scattered atoms at k=kS
spontaneous FWM
k0
k0kS
kS
k0 k0
Create an m = 0 condensate w/ raman pulse.
Split BEC into two momentum components with Bragg pulse: +/- k0
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The “intuitive” resultThe “intuitive” result
Scattered pairs are correlated…
0 Δt
P(Δt)
k0
k0
kS
kS
Like in photon pairs: “Enhanced
coincidence rate when phase
matching condition is met.”
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Beyond Optics: smaller Beyond Optics: smaller spheresphere
|kS| < |k0|
k0
k0
kS
kS
Energy Cost to put atom into scattered mode (still overlapped w/
condensate).
k0 k0
kS
kS
(per atom)
Energy gain from removal of atom from
condensate mode <
““energy balance”energy balance”
V. Krachmalnicoff, J.-C. Jaskula, M. Bonneau, V. Leung, G. B. Partridge, D. Boiron, C. I. Westbrook, P. Deuar, P. Zin, M. Trippenbach, K. Kheruntsyan, Phys. Rev. Lett. 104,150402 (2010).
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Plus, the sphere’s not a Plus, the sphere’s not a spheresphere
After colliding, atoms still have to get out of the region of the condensates.
i.e. they roll down the mean field hill: V = 2g(r,t)
But the hill is collapsing out from under them.
Anisotropy of BEC’s leads to directional acceleration
Lesson Learned:Do Q.O. experiments using atoms, but be careful about
simple 1:1 intuition. There are differences, for better or worse…
Analogy? ponderomotive force in high harmonic generation
(Balcou et al PRA 1997)Phys. Rev. Lett. 104,150402 (2010).
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Intermediate Q.O.: Relative N Intermediate Q.O.: Relative N SqueezingSqueezing
Heidmann et al. PRL 59 2555 (1987)
BA
BA
II
IIR
A
B
Measurement of intensity noise between “twin” beams.
Reduction in noise, 30% below the shot noise limit!
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New Atom PairsNew Atom PairsRF + Bragg pulse.Optical Trap BEC
Back-to-Back Correlations: 3600 shotsCollision along long axis + better repeatability gives
improved S/N.Now what about squeezing?
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Matter Wave N SqueezingMatter Wave N Squeezing
1,
M
ji
jiij
NN
NNM
Divide scattered halo into sections, compare number difference in
geometrically opposing zones to that of non-opposing zones.
(for uncorrelated N, i.e. shot noise)
1
M
M 16 zones
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Details…Details…
Detail 1:
Raw data ~ -0.5 dB squeezing
Why isn’t it perfect?
(partly b/c its an experiment)
Specifically, the detector efficiency, , limits the measured variance.
Perfect correlations: M = (1- ) = 0.6 (“open area”) : -3 dB
= .13 (best estimate): -13 dB
Detail 2:Effect of of correlation length:
~Measurement bandwidth
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What’s next?What’s next?
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But! Trapped He* gases are prone to loss due to Ionization-enhanced
inelastic loss processes.
Spin Polarization in the mJ = 1 provides stabilization by ~5 orders
of magnitude.
What about other states and combinations of states?
State specific loss constants unconfirmed experimentally (only mJ = 1 is magnetically trappable)
With optical trap, we can think about using different spin states (mJ = +1,-1,0)
spin mixtures, spinor condensates …
RF transfers: spin mixtures
Alternate Future: spin mixturesAlternate Future: spin mixtures
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Loss Rates in a spin Loss Rates in a spin mixturemixture
Inelastic Loss Experiment 1: Put them all together and see what
survives…
“Small” loss rate: 01, 0-1, 11, -1-1
“Large” loss rate: 00, ±1
G. B. Partridge et al., Phys. Rev. A 81, 053631 (2010).
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Quantitative Loss RatesQuantitative Loss Rates
00 = 6.6(4) × 10 −10 cm3/s
±1 = 7.4(10) × 10 −10 cm3/s.
Not necessarily prohibitive! (for certain things…)
Inelastic Loss Experiment 2: Make careful measure of the dominant processes 00 ±1.
G. B. Partridge et al., Phys. Rev. A 81, 053631 (2010).
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SummarySummary
1. Quantum Atom Optics: Spontaneous FWM of deBroglie matter waves.
• Don’t forget they’re atoms.
2. Relative Number Squeezing for correlated atom pairs.
• Atomic version of a Quantum Optics Classic.
3. Spin Mixtures in of He* ? • Stay tuned…
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Thanks!
Questions?