Deceleration and trapping of heavy diatomic molecules for precision tests of fundamental symmetries. Steven Hoekstra

Transcription

1 Deceleration and trapping of heavy diatomic molecules for precision tests of fundamental symmetries Steven Hoekstra

2 Deceleration and trapping of heavy diatomic molecules for precision tests of fundamental symmetries Steven Hoekstra - Introduction: why we do this - Stark deceleration, and its limitations - Our approach: ring deceleration + lasercooling of heavy diatomics - Outlook

3 Our main motivation: Selected molecules offer unique sensitivity to probe new physics: by precision measurements, Standard Model predictions and alternative theories can be tested

4 Our main motivation: Selected molecules offer unique sensitivity to probe new physics: by precision measurements, Standard Model predictions and alternative theories can be tested - electric dipole moment of the electron because of huge internal fields in polar molecules (YbF, PbF, PbO, ThO, WC, HfF + ) - time-variation of the constants because of high sensitivity of tunneling to mass (NH3) or close-lying states with different shifts (CO) - (nuclear-spin dependent) parity violation because of close-lying rotational and vibrational states with opposite parity (BaF, SrF, RaF)

5 Our main motivation: Selected molecules offer unique sensitivity to probe new physics: by precision measurements, Standard Model predictions and alternative theories can be tested - electric dipole moment of the electron because of huge internal fields in polar molecules (YbF, PbF, PbO, ThO, WC, HfF + ) - time-variation of the constants because of high sensitivity of tunneling to mass (NH3) or close-lying states with different shifts (CO) - (nuclear-spin dependent) parity violation because of close-lying rotational and vibrational states with opposite parity (BaF, SrF, RaF) Cold molecules offer increased sensitivity and precision: - at low temperatures, fewer states are populated - precision of measurements ultimately limited by interaction time trapped molecules / fountains / slow beams The ultimate experiment is done by precision spectroscopy on trapped ultracold molecules

6 Techniques Indirect Direct Carr, Demille, Krems, Ye: special issue on cold molecules, New Journal of Physics (2009)

7 Stark Deceleration - Can be used to decelerate neutral molecules - First succesfully demonstrated in 1999: - Based on interaction of electric dipole with electric fields - Favorable molecules: light with large dipole moment OH, CO, NH3, NH, H2CO, H2O

8 Starting with a pulsed molecular beam: P ~10 5 mbar P ~2 bar P ~10 8 mbar Cooling of internal degrees of freedom in a (pulsed) supersonic expansion High initial phase-space density Ammonia seeded in xenon Neat ammonia beam But: high velocity in the lab frame, typically in the m/s range ,000 1,500 Velocity (ms )

9 Starting with a pulsed molecular beam: P ~10 5 mbar P ~2 bar P ~10 8 mbar Cooling of internal degrees of freedom in a (pulsed) supersonic expansion High initial phase-space density Ammonia seeded in xenon Neat ammonia beam But: high velocity in the lab frame, typically in the m/s range ,000 1,500 Velocity (ms ) U pot = W Stark W Stark = µ E F Stark = W Stark

10 Stark decelerator: principle of operation Molecules in low-field seeking states gain Stark energy at the expense of kinetic energy Energy (cm -1 ) J = Electric field strength (kv/cm) M J

11 Stark decelerator: schematic overview PMT LIF zone trap Stark decelerator hexapole skimmer m photodissociation laser pulsed valve detection laser Electric fields: 40 kv / 4 mm Switched on/off in <1 µs Number of deceleration stages: ~100

12 Example measurements: deceleration of OH molecules 2.2 Arrival time spectra, 100 m/s and 30 m/s deceleration Measured with CW laser, F=2 component only Intensity Arrival time (ms)

13 5 Velocity tunable packets of molecules Normalized intensity experimental time-offlight profiles: OH molecules Tunable velocity range: m/s Completely state-selected packets Ideal starting point for collision experiments time of flight (ms) Joop J. Gilijamse, Steven Hoekstra, Sebastiaan Y. T. van de Meerakker, Gerrit C. Groenenboom, and Gerard Meijer Science (2006)

14 Example measurements: electric trapping Trap on Intensity (arb.units) Trapping of OD Temperature ~ 10 mk Trapping time ~ seconds detection time (ms) S. Hoekstra et al, PRL 98, (2007)

15 Towards larger and heavier molecules High-Z enhancements for many fundamental physics tests The challenges: Larger mass requires a longer decelerator - but long decelerators suffer from instabilities... Stark curves of heavy molecules are unfavorable: high-field seeking! (J,M) Stark curves of SrF

16 Ring decelerator: molecular conveyer belt 12)# ,"-%&%"#+.//0 ; 6 : 5! :5 :6!"#$%&'(%#)*+,"-%&%"#+.//0! <=>?/ 75 ;5 65 :5 First realization of ring decelerator (CO deceleration): Osterwalder, PRA (2010)

17 Ring decelerator: molecular conveyer belt 12)# ,"-%&%"#+.//0 ; 6 : 5! :5 :6!"#$%&'(%#)*+,"-%&%"#+.//0! <=>?/ 75 ;5 65 :5 First realization of ring decelerator (CO deceleration): Osterwalder, PRA (2010) Advantages of a ring decelerator: - Molecules remain in low electric fields, so low-field seeking part of Stark curve can be used. - Inherently stable -> no limit to the length Challenges: - Electronics

18 Numerical calculations: acceptance 78*$.238.3,23+#4&'5,/06.1 "#$%&'()&$*+,23+#4&'5,/06.1!!! "#$%&'()&$*+,-#.&'&#$,/001! *1 91! 78*$.238.3,-#.&'&#$,/001! "#$%&'()&$*+,23+#4&'5,/06.1! 41 )1 78*$.238.3,23+#4&'5,/06.1! "#$%&'()&$*+,-#.&'&#$,/001!! 78*$.238.3,-#.&'&#$,/001 Deceleration and trapping of heavy diatomic molecules using a ring decelerator J. van den Berg, S. Hoekman, E. Prinsen, S.Hoekstra, arxiv: (2011)

19 Numerical calculations: acceptance 10 5 Total 3D acceptance (mm 3 (m/s) 3 ) kv 8 kv 8 kv YbF(5,0) WFS YbF(0,0) AG Decelerator length (m) Deceleration and trapping of heavy diatomic molecules using a ring decelerator J. van den Berg, S. Hoekman, E. Prinsen, S.Hoekstra, arxiv: (2011)

20 Decelerator for heavy molecules (computer render)

21 Decelerator for heavy molecules (computer render)

22 Decelerator for heavy molecules (computer render)

23 Decelerator for heavy molecules

24 Decelerator for heavy molecules Distance between ring-electrodes: 0.9 mm 8 Sets of electrodes, Phase-shifted sine waves (30 khz - DC) Voltage applied: ±5 kv Total length: ~ 5 meter, ~3500 electrodes

25 Now KVI:

26 Not limited to SrF At the KVI we can also produce radioactive species (RaF, RaO) Many of these molecules are also promising lasercooling candidates Lasercooled RaF as a promising candidate to measure molecular parity violation T. Isaev, S. Hoekstra, R. Berger Phys. Rev. A (2010)

27 Conclusions - We are setting up a unique new experiment to decelerate and trap heavy diatomics molecules - The goal is to perform precision spectroscopy on ultracold and trapped heavy diatomic molecules - The ring decelerator is a general device, not limited to SrF - First trapping experiments (NH3) planned this summer, first deceleration of SrF in 2012

28 Conclusions - We are setting up a unique new experiment to decelerate and trap heavy diatomics molecules - The goal is to perform precision spectroscopy on ultracold and trapped heavy diatomic molecules - The ring decelerator is a general device, not limited to SrF - First trapping experiments (NH3) planned this summer, first deceleration of SrF in 2012 Acknowledgements: FHI Berlin: Bas van de Meerakker Andreas Osterwalder Henrik Haak Gerard Meijer Klaus Jungmann KVI Groningen Steven Hoekstra Joost van den Berg Corine Meinema Imko Smid VU Amsterdam: Rick Bethlem Wim Ubachs Hans Wilschut Samuel Hoekman Eric Prinsen Leo Huisman TU Darmstadt Timur Isaev Robert Berger

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