1. A molecular fountain Cunfeng Cheng 2017-06-19
LaserLaB, Department of Physics and Astronomy
Vrije Universiteit Amsterdam
De Boelelaan 1081, 1081 HV Amsterdam
The Netherlands

2. Precision measurements on molecules
Tests of discrete symmetries (search for eEDM…)
Testing time-invariance of fundamental constants
∆𝑓 𝑓 = 𝐾 𝜇 ∆𝜇 𝜇
𝐾 𝜇 ~−0.5
for vibrational transition
𝐾 𝜇 ~−1.0
for rotational transition

3. Transition measurement on molecules
frequency uncertainty: 𝜎= ∆𝑓 𝑓 1 𝑁
MW cavity
0.88/Δt
8.8 kHz
880 Hz
v = 500 m/s, L = 5 cm; Δt = 0.1 ms, Δf = 8.8kHz 3

4. Transition measurement in a fountain
But we need slow (< 2m/s) and cold (~1 μK) molecules!!
v = 1.5 m/s, L = 11 cm; Δt = 0.3 s; Δf = 1.6 Hz 4

5. A molecular beam
Pulse Valve
Ammonia seeded
in Xenon

6. A dipole in an inhomogeneous E-field6

7. An array of inhomogeneous E-fields
Stark decelerator
v = 90 m/s
v = 300 m/s
Stark energy
Bethlem, et al. PRL 83: , 1999 7

8. Quintero-Pérez, et al. PRL 110:133003, 2013
Ring type decelerator
v = 90 m/s
Quintero-Pérez, et al. PRL 110:133003, 2013

9. Amsterdam
< 2m/s
1mK
Making cold ammonia
90m/s
30mK
300m/s 1K

10. Electric lens system Free fly region for spectroscopy Tx,y < 10 uK
(All fields off!)
Tx,y < 10 uK
Tz < 1 uK
Quad on
Ring on
Cheng, et al. PRL 117:253201, 2016

11. A molecular fountain
14NH3
time (ms)

12. Molecular fountain signal
First 15NH3 fountain!
1.5m/s Δt=120ms

13. To be continued…
We demonstrated the molecular fountain with free flight time up to 266 ms.
First demonstration of 15NH3 fountain.
Demonstrate spectroscopy with Microwave or IR.
Look for two photon transitions in ammonia.

14. Thanks for your attention
LaserLaB, Amsterdam:
Aernout van der Poel
Marina Quintero Pérez
Thomas Wall
Paul Jansen
Rob Kortekaas
Wim Ubachs
Rick Bethlem

16. Molecular fountain with ammonia
Nice molecule, various transitions; Good laser source
Large dipole moment and small mass; can be effectively decelerated
Large vapor pressure; intense molecular beam
J. van Veldhoven et al. EPJD 31, 337 (2004).
H. L. Bethlem et al. EPJ Special Topics 163, 55 (2008).