Progress on Optical
+
Rotational Cooling of SiO
Patrick Stollenwerk / Yen-Wei Lin / Brian Odom
Molecular Ion Trapping Group @ Northwestern
University
• Motivation: Ground state preparation
and coherent control of a molecule
• Challenges and Advantages of SiO+
• Rotational Cooling
• Fluorescence imaging as state readout
Coulomb crystal,
0.6mm x 0.2mm (x 0.2mm).
Ion string, 0.8mm long.
Coulomb crystal,
0.6mm x 0.2mm (x 0.2mm).
Ion string, 0.8mm long.
Coulomb crystal,
0.6mm x 0.2mm (x 0.2mm).
Ion string, 0.8mm long.
Coulomb crystal,
0.6mm x 0.2mm (x 0.2mm).
Ion string, 0.8mm long.
Coulomb crystal,
0.6mm x 0.2mm (x 0.2mm).
Ion string, 0.8mm long.
The same, but more! I.E. Image and
coherently control molecules.
p+
e-
Sensitive probe to time variation of
fundamental constants
Ultracold chemistry
NJP 11, 055049 (2009)
Quantum information processing
28Si:
92%; 16O: 99.8%.
Zero nuclear spin: no hyperfine
structure.
(Nearly) Diagonal FrankCondon Factors in B-X
160 (5000) photons without (with)
broadband vibrational repumping
~43 GHz spacing between
lowest rotational states
Small predicted dissociation
cross section from B-state of
order 10-19 cm2 (difficult!)
SiO+ potential curves
B2Σ+
X2Σ+
First attempt: ablation loading. It
works for Ba+!
Mass Spec of ION SPECIES Produced from Ablation
Laser ablation
produces Na+, Si+,
SiOH+ etc., but not
much SiO+.
Ref: J. Phys. Chem. A
113, 10880 (2009).
SiO+, m=44
SiO in test vacuum chamber
Ignore the ions produced by ablation and ionize the neutrals!
Ion signal yield vs. wavelength
Mass spec. in ion trap
HX(0,0)
Ba+
Counts
HX(1,1)
SiO+
HX(2,2)
Mass (amu)
Typically load 500+ Ba+ and 100+ SiO+.
Lighter mass more tightly confined -> dark core
formation
Ba+ sympathetically cools SiO+
No short-range collision -> internal state remains hot
Dark 137Ba+ ions
Dark core: SiO+
Bright 138Ba+ ions
B2Σ+->X2Σ+(v=0,v’’=0)
300 K
P-branch
1000 K
‘’
Relative Population
R-branch
B
N=
40 (+)
39 (-)
38 (+)
37 (-)
...
2 (+)
1 (-)
0 (+)
2 (+)
1 (-)
0 (+)
385nm
...
N’’= 40 (+)
39 (-)
38 (+)
37 (-)
X
Rotational Cooling Laser(s?)
Population build up in lowest
two parity states
MaiTai FS laser source
(Spectra-Physics)
used for pulse
shaping
SiO+ P/R branches are
separated so a razor
blade acts as a
sufficient mask
Technique already
demonstrated on
AlH+
Nature Communications 5, 4783 (2014)
wavelength
Drive P-branch transitions until everything is pumped into rotational
ground state (~1-10 ms). Cooling rate currently limited by laser
intensity.
N J P
B(v=0)
1 1.5 0.5 -
Photon budget
160 without any repumping
~5000 with vibrational
repumping v=1, 2, 3..
P11(1)
N’’ J’’ P’’
0 0.5 +
τ =11 μs
P12(1)
τ =~350 μs
A
τ =70 ns
8 MHz
X(v’’=0)
1 1.5 0.5 -
385 nm
Semi-closed
0 0.5 +
X(v’’>0)
R-branches
P-branches
• Same idea as rotational cooling! SHG of Spectra-Physics
Tsunami FS laser used as broadband source
• All other vibrational transitions separated by >103 cm-1!
0.1% Total Detection Efficiency (using Ba+ measurement)
Reliable loading method established
Lasers:
FS broadband laser pulse shaping for rotational
cooling cutoff independently measured
FS broadband laser vibrational repump laser @403
nm ready
CW laser@385nm is prepared for fluorescence
detection
Imaging background has been
characterized
Pulsed fluorescence detection
Obtain first single molecular ion image in
free space with CW laser
Begin microwave control of N=0 and N=1
rotational states
Our Group!
PI
Funding
Agencies:
Brian Odom
Research
Fellows
Matt Dietrich
Zeke Tung
Grad
Students
Mark Kokish
Yen-Wei Lin
Chris Seck
Ming-Feng Tu
Past
members
Jason Nguyen
Joan Marler
Chien-Yu Lien
Vaishnavi Rajagopal
David Tabor
Undergrad Eugene Wu