Towards coherent control of cold molecule formation in a magnetooptical trap

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Towards coherent control of cold molecule
formation in a magneto-optical trap

• Benjamin L. Brown, Alexander J. Dicks and
• Ian A. Walmsley
• Clarendon Laboratory, University of Oxford
• Institute of Optics, University of Rochester

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Goal Ultracold Molecules

• Motivation
• Recent successes from atom cooling
• Can these be translated to molecules?
• Potential Applications
• Collision studies
• Exploration of many-body systems
• Molecular spectroscopy
• Molecular BEC
• Molecule optics à la atom optics
• New systems for quantum computation

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Recent Advances in Ultracold Molecules

• Atom cooling techniques do not work for molecules
• Direct cooling schemes
• Buffer gas cooling, electrostatic slowing
• thusfar limited to mK
• CW Photoassociation (PA) of ultracold atoms in a
  MOT
• PA of homonuclear alkali metals Rb, Cs, K
• PA of heteronuclear polar species RbCs, RbK,
  NaCs
• reliance on spontaneous emission limits
  state-selectivity
• Synthesis of molecules in BECs via a Feshbach
  resonance
• ? molecules are formed in long-range states

Gabbanini et al., PRL 84, 2814 (2000). Fioretti
et al., PRL 80, 4402 (1998). Nikolov et al., PRL
82, 703 (1999).
Kerman et al., PRL 92, 033004 (2004). Mancini et
al., PRL 92, 133203 (2004). Haimberger et al.,
PRA 70, 021402 (2004).
Donley et al., Nature 417, 529 (2002) Regal et
al., Nature 424, 47 (2003) Herbig et al.,
Science 301, 1510 (2003).
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Approach Coherent Control

• Yet unobtained
• translationally ultracold
• (T lt 1 mK)
• ground singlet v0, J0

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Approach Coherent Control

• Yet unobtained
• translationally ultracold
• (T lt 1 mK)
• ground singlet v0, J0

• Different Approach to PA
• Use shaped broadband optical pulses to promote
  stimulated population transfer to target
• Why femtosecond pulses?
• Replace several CW lasers with one broadband
  laser
• More parameters by which to control collision
  process
• Strong fields for efficient population transfer

Koch et al., PRA 70 013402 (2004) Luc-Koenig et
al., physics/0407112 (in press).
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Potential Coherent Control Schema

• Pump-dump

Single pulse Raman-like walk

• Adiabatic inversion
• Avoid population cycling by introduction of time
  asymmetry

• Gain inward momentum on R-3
• Mixture of strong field population transfer and
  free evolution

Cao et al., PRL 80 1406 (1998) Vala et al., PRA
63 013412 (2001).
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Pulsed Photoassociation of Rb
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Pulsed Photoassociation of Rb
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Pulsed Photoassociation of Rb
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Pulsed Photoassociation of Rb
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CW vs. Pulsed Photoassociation
Performed comparative studies of different
photoassociation (PA) sources

• 87Rb MOT, detection of a3Su ground state
  molecules

PA by CW laser, I 103 W cm-2 red-detuned
0.8 cm-1 from D2
PA by pulsed Tisapph laser ?0
785 nm, I 107 W cm-2

• Increased Rb2 production
• Verification of Gabbanini et al., PRL 84 2814
  (2000).

• Suppression of Rb2 production
• Photodissociation of Rb2

or
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Test of Short vs. Chirped Pulses
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Test of Short vs. Chirped Pulses
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Test of Short vs. Chirped Pulses
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Test of Short vs. Chirped Pulses
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Short vs. Chirped Pulses Results
Short pulses (100 fs) vs. chirped pulses (6.7 ps)
of equal energy

• Rb2 yield depends on the shape of the PA laser
  pulse
• Coherent phenomenon
• Pulses cause either
• Suppression (possible coupling to (1)3Sg)
• Photodissociation
• Numerical simulations ongoing

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Summary and Prospects

• Summary
• Applying femtosecond pulses to MOT causes
  suppression/photodissociation of triplet Rb2
• Chirped pulses are more efficient than short
  pulses at stimulating this effect
• Coherent phenomenon
• Physical explanation unclear simulations
  ongoing
• Prospects
• Closed loop coherent control is a novel approach
  to the problem of synthesizing v0, J0 ultracold
  molecules
• Focus on singlet Rb2
• Two-color state-selective singlet detection
  scheme in development

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Test of Short vs. Chirped Pulses
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Test of Short vs. Chirped Pulses
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Test of Short vs. Chirped Pulses
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Test of Short vs. Chirped Pulses
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Pulsed Photoassociation of Rb
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Closed Loop Control Experiment
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Potential Coherent Control Schema

• Pump-dump

• Avoid rogue photodissociation by introduction of
  time asymmetry

Cao et al., PRL 80 1406 (1998) Vala et al., PRA
63 013412 (2001).
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Potential Coherent Control Schema

• Pump-dump

• Avoid rogue photodissociation by introduction of
  time asymmetry

Cao et al., PRL 80 1406 (1998) Vala et al., PRA
63 013412 (2001).
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Potential Coherent Control Schema

• Pump-dump

• Single pulse Raman-like walk

• Avoid rogue photodissociation by introduction of
  time asymmetry

• Mixture of strong field population transfer and
  free evolution

Cao et al., PRL 80 1406 (1998) Vala et al., PRA
63 013412 (2001).
Brown et al., in preparation.
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• PA efficiency depends on the shape of the PA
  laser pulse
• Coherent phenomenon
• Pulses cause either
• Suppression (possible coupling to (1)3Sg)
• Photodissociation
• Numerical simulations ongoing