IGERT poster v5 1234
+ Towards Doppler Cooling of SiO D. A. Tabor and B. Odom Department of Physics and Astronomy Northwestern University, Evanston, IL http://faculty.wcas.northwestern.edu/brian-odom/
Introduction In vacuum, a combination of static and time-varying electric fields confine ions. Confinement duration can exceed hours, and environmental isolation allows for coherent quantum manipulation.
Rendering of a ion trap. Voltages applied to the electrodes (green, orange) create confinement.
493 nm
6 P1/2 649 nm
5 D 3/2
6 S1/2 Ba+ energy levels.
Why molecules?
Our Goal
Ion Trapping and Doppler Cooling
Are Fundamental "Constants" Really Constant?
A closed cycling scheme can be formed in Ba+ with two lasers.
Precisely because of their rich internal structure, molecules are much more difficult to control than atoms. If on-demand control of molecular vibrations and rotations could be achieved, molecular complexity could be turned into an advantage, with a number of applications becoming possible for the first time.
Only atomic ions have thus far been Doppler cooled. We aim to Doppler cool the translational motion of a molecular ion, demonstrating a significant expansion of the class of Doppler-coolable ions, and have identified SiO+ as a favorable target.
Cooling to sub-microkelvin temperatures can be achieved if the trapped ion species possesses a rapid, closed transition. The driving laser is red-detuned so that the absorbed photon is less energetic than the emitted photon.
Experimental realization of an ion trap for 138Ba+.
http://www.forbrf.lth.se/
+ Suitability of SiO for Cooling Electronic Level Structure of SiO+
Desirable Features of SiO+
Dye laser (Sytryl 8 dye)
BBO Doubling Crystal 100’s mW, 770 nm
1’s mW, 385 nm
Variable Attenuator
(Probe Light)
8 W, 532 nm
Pulsed Nd:YAG laser w/ output doubling
• The A->X transition rate is sufficiently fast so as to preclude population build up in the dark A state.
Results and Analysis SiO+ is produced by ablating a silicon sample in a O2 environment. The X(v=0) to B(v=0) transition is driven by a tunable probe beam around 385 nm, which passes through the cloud of ablation products.
1’s-10’s mW, 1064 nm Pulsed Nd:YAG laser
(Ablation Light) Vacuum chamber filled w/ 100 mTorr O2
Proposed Vibrational Repumping
Calculated Rates of Decay and Vibrational Leak
Silicon sample
A PMT detector, not pictured in the diagram at right, detects florescence from SiO+ molecules decaying from B(v=0) back into X(v=0).
Simulated Cooling Rates
_
|e 1,1/2
Our current efforts include assembling our vacuum system, which contains our completed trap and ion production source. Additionally, we are developing methods of spectrally filtering the output of a femtosecond pulse laser. By minor extension of established work with this technique [1], we will be able to drive multiple repump transitions with a single laser source.
=3 ms
=110 ms
=11 s 01
03
02
=70 ns 00
20
10
v =0
’’=500 s 30
nm
X
’’=27 s ’’=3 s
2
v =1 +
31
21
R6
R7
R8
| i P’ v’, J’ _
|g 0,5/2
|g +0,5/2
R1 R2
|g +2,3/2 _
|g 2,3/2 _
|g 2,1/2
nm
’’=6 s
2
’’=1 s
R5
2
v =2
|e +0,1/2
40
32
_
|e 0,1/2
= 01
’’=3 s
_
|e 0,3/2
00= 385 nm
v =3
From the B(v=0) state, decay to the X(v=0) state is strongly preferred and very rapid in comparison to other allowed decays. Vibrational redistribution within the X state is extremely slow by comparison.
|e +0,3/2
40
v=0
12
B
R3
|g +2,1/2
R4 |g +1,3/2
Assembled trap for SiO+ cooling.
_
C1 C2 C3 C4
PR2 PR1
The above data shows our measured emission spectrum of SiO+ decaying from B(v=0) to X(v=0). Substructure in the spectrum results from different rotational states within B(v=0) decaying into different rotational states within X(v=0). Transitions in which the rotational quantum number decreases are labeled P-Branch, and those in which it is unchanged are labeled R-Branch. The spectrum is in good agreement with previously reported spectroscopy.
Ongoing Work
|e +1,1/2 +
Sub-Kelvin chemical reactions between molecular ions and neutral species are predicted to exhibit interesting quantum effects, including reaction cross-sections which depend strongly on the internal molecular state.
Experimental Methodology
Details of Cycling Scheme 2
What is Chemistry Like Below 1 Kelvin?
As a first step toward trapping and cooling SiO+, we have performed florescence spectroscopy on SiO+. In this way we confirm our production method and locate the cooling transition.
• Highly diagonal FranckCondon factors ensure that decay from B(v=0) strongly tends to X(v=0), creating a nearly-closed cycling transition.
are subdivided into vibrational levels [e.g. X(v=0,1,2...)], which are further divided into rotational levels. The above potential energy curves determine the energy spacings.
Time-variation of fundamental "constants" is generally expected in many extensions of the Standard Model. There is currently one claim of evidence for variation of the electron-proton mass ratio on cosmic time scales, making improved laboratory searches quite interesting.
Initial Spectroscopy
• The B->X transition is rapid and occurs at an accessible wavelength (385 nm).
The three lowest-lying states of SiO+, denoted X, A, and B,
Motivation
|g 1,3/2 _
|g 1,1/2
|g +1,1/2
Spectral filtering of the output of a short-duration pulse laser..
|g +0,3/2 _
|g 0,3/2
v=0 =7.6 ms A 04
=4.2 ms A 03
=2.8 ms A 02
=2.4 ms
A 00
=70 ns
4
=157 s
3
=221 s
2
=368 s
1
=790 s
X 2
+
0
=4.1 ms
2
00
A
A 01
+
=3.4 ms
B 2
v =4 v =3 v =2 v =1 v =0
Decay from the B(v=0) state to all A states is low compared to the decay from those states to X(v=0). For this reason, the intervening A state does not significantly interfere with using the B-X transition. It does cause rotational diffusion (not pictured in this simplified diagram).
Our proposed repumping scheme, with rotational sublevels shown explicitly, is depicted above. As many as ten potential repumping transitions are identified, although we evaluate the viability of using various limited subsets of these. The labels C, R, and PR correspond to cooling, repump and parity repump transitions respectively. The B and X states are labeled e and g respectively. States are labeled |e/g Pv,J> denoting parity (P), vibrational level (v) and total angular momentum (J).
Schematic:
Shown above is the number of photons scattered by an SiO+ ion before leaking out of the cycling scheme, as calculated by a rate-equation simulation. Different plots correspond to different numbers of applied repump lasers. The shaded band represents the approximate number of photon scatters required to cool to the Doppler limit from room temperature.
Pulse Distribution: Normalized Amplitude
_
|g 0,1/2 |g +0,1/2
1.0
0.8
0.6
0.4
0.2
0.0 26 240
26 260
26 280
26 300
26 320
26 340
26 360
Frequency (cm-1)
[1] M. Viteau et al., Science, 321, 232 (2008)
Introduction In vacuum, a combination of static and time-varying electric fields confine ions. Confinement duration can exceed hours, and environmental isolation allows for coherent quantum manipulation.
Rendering of a ion trap. Voltages applied to the electrodes (green, orange) create confinement.
493 nm
6 P1/2 649 nm
5 D 3/2
6 S1/2 Ba+ energy levels.
Why molecules?
Our Goal
Ion Trapping and Doppler Cooling
Are Fundamental "Constants" Really Constant?
A closed cycling scheme can be formed in Ba+ with two lasers.
Precisely because of their rich internal structure, molecules are much more difficult to control than atoms. If on-demand control of molecular vibrations and rotations could be achieved, molecular complexity could be turned into an advantage, with a number of applications becoming possible for the first time.
Only atomic ions have thus far been Doppler cooled. We aim to Doppler cool the translational motion of a molecular ion, demonstrating a significant expansion of the class of Doppler-coolable ions, and have identified SiO+ as a favorable target.
Cooling to sub-microkelvin temperatures can be achieved if the trapped ion species possesses a rapid, closed transition. The driving laser is red-detuned so that the absorbed photon is less energetic than the emitted photon.
Experimental realization of an ion trap for 138Ba+.
http://www.forbrf.lth.se/
+ Suitability of SiO for Cooling Electronic Level Structure of SiO+
Desirable Features of SiO+
Dye laser (Sytryl 8 dye)
BBO Doubling Crystal 100’s mW, 770 nm
1’s mW, 385 nm
Variable Attenuator
(Probe Light)
8 W, 532 nm
Pulsed Nd:YAG laser w/ output doubling
• The A->X transition rate is sufficiently fast so as to preclude population build up in the dark A state.
Results and Analysis SiO+ is produced by ablating a silicon sample in a O2 environment. The X(v=0) to B(v=0) transition is driven by a tunable probe beam around 385 nm, which passes through the cloud of ablation products.
1’s-10’s mW, 1064 nm Pulsed Nd:YAG laser
(Ablation Light) Vacuum chamber filled w/ 100 mTorr O2
Proposed Vibrational Repumping
Calculated Rates of Decay and Vibrational Leak
Silicon sample
A PMT detector, not pictured in the diagram at right, detects florescence from SiO+ molecules decaying from B(v=0) back into X(v=0).
Simulated Cooling Rates
_
|e 1,1/2
Our current efforts include assembling our vacuum system, which contains our completed trap and ion production source. Additionally, we are developing methods of spectrally filtering the output of a femtosecond pulse laser. By minor extension of established work with this technique [1], we will be able to drive multiple repump transitions with a single laser source.
=3 ms
=110 ms
=11 s 01
03
02
=70 ns 00
20
10
v =0
’’=500 s 30
nm
X
’’=27 s ’’=3 s
2
v =1 +
31
21
R6
R7
R8
| i P’ v’, J’ _
|g 0,5/2
|g +0,5/2
R1 R2
|g +2,3/2 _
|g 2,3/2 _
|g 2,1/2
nm
’’=6 s
2
’’=1 s
R5
2
v =2
|e +0,1/2
40
32
_
|e 0,1/2
= 01
’’=3 s
_
|e 0,3/2
00= 385 nm
v =3
From the B(v=0) state, decay to the X(v=0) state is strongly preferred and very rapid in comparison to other allowed decays. Vibrational redistribution within the X state is extremely slow by comparison.
|e +0,3/2
40
v=0
12
B
R3
|g +2,1/2
R4 |g +1,3/2
Assembled trap for SiO+ cooling.
_
C1 C2 C3 C4
PR2 PR1
The above data shows our measured emission spectrum of SiO+ decaying from B(v=0) to X(v=0). Substructure in the spectrum results from different rotational states within B(v=0) decaying into different rotational states within X(v=0). Transitions in which the rotational quantum number decreases are labeled P-Branch, and those in which it is unchanged are labeled R-Branch. The spectrum is in good agreement with previously reported spectroscopy.
Ongoing Work
|e +1,1/2 +
Sub-Kelvin chemical reactions between molecular ions and neutral species are predicted to exhibit interesting quantum effects, including reaction cross-sections which depend strongly on the internal molecular state.
Experimental Methodology
Details of Cycling Scheme 2
What is Chemistry Like Below 1 Kelvin?
As a first step toward trapping and cooling SiO+, we have performed florescence spectroscopy on SiO+. In this way we confirm our production method and locate the cooling transition.
• Highly diagonal FranckCondon factors ensure that decay from B(v=0) strongly tends to X(v=0), creating a nearly-closed cycling transition.
are subdivided into vibrational levels [e.g. X(v=0,1,2...)], which are further divided into rotational levels. The above potential energy curves determine the energy spacings.
Time-variation of fundamental "constants" is generally expected in many extensions of the Standard Model. There is currently one claim of evidence for variation of the electron-proton mass ratio on cosmic time scales, making improved laboratory searches quite interesting.
Initial Spectroscopy
• The B->X transition is rapid and occurs at an accessible wavelength (385 nm).
The three lowest-lying states of SiO+, denoted X, A, and B,
Motivation
|g 1,3/2 _
|g 1,1/2
|g +1,1/2
Spectral filtering of the output of a short-duration pulse laser..
|g +0,3/2 _
|g 0,3/2
v=0 =7.6 ms A 04
=4.2 ms A 03
=2.8 ms A 02
=2.4 ms
A 00
=70 ns
4
=157 s
3
=221 s
2
=368 s
1
=790 s
X 2
+
0
=4.1 ms
2
00
A
A 01
+
=3.4 ms
B 2
v =4 v =3 v =2 v =1 v =0
Decay from the B(v=0) state to all A states is low compared to the decay from those states to X(v=0). For this reason, the intervening A state does not significantly interfere with using the B-X transition. It does cause rotational diffusion (not pictured in this simplified diagram).
Our proposed repumping scheme, with rotational sublevels shown explicitly, is depicted above. As many as ten potential repumping transitions are identified, although we evaluate the viability of using various limited subsets of these. The labels C, R, and PR correspond to cooling, repump and parity repump transitions respectively. The B and X states are labeled e and g respectively. States are labeled |e/g Pv,J> denoting parity (P), vibrational level (v) and total angular momentum (J).
Schematic:
Shown above is the number of photons scattered by an SiO+ ion before leaking out of the cycling scheme, as calculated by a rate-equation simulation. Different plots correspond to different numbers of applied repump lasers. The shaded band represents the approximate number of photon scatters required to cool to the Doppler limit from room temperature.
Pulse Distribution: Normalized Amplitude
_
|g 0,1/2 |g +0,1/2
1.0
0.8
0.6
0.4
0.2
0.0 26 240
26 260
26 280
26 300
26 320
26 340
26 360
Frequency (cm-1)
[1] M. Viteau et al., Science, 321, 232 (2008)
