Experiments with Stark-decelerated and trapped polar molecules Steven Hoekstra Molecular Physics Department ( Gerard Meijer) Fritz-Haber-Institutder Max-Planck-Gesellschaft Berlin, Germany Steven Hoekstra Molecular Physics Department ( Gerard Meijer) Fritz-Haber-Institutder Max-Planck-Gesellschaft Berlin, Germany

Introduction & Motivation: What to do with Stark-decelerated and trapped polar molecules Using the long interaction time: - High precision measurements / spectroscopy - Understanding trap loss mechanisms: Blackbody radiation - Measurement of the lifetime of metastable CO Using the low energy: - Collision experiments - Reflection of OH molecules by a magnetic mirror - Dipole-dipole interactions, ultracold collisions - Towards a higher phase space density: Magnetic trapping and accumulation of NH molecules

Introduction & Motivation: What to do with Stark-decelerated and trapped polar molecules Using the long interaction time: - High precision measurements / spectroscopy - Understanding trap loss mechanisms: Blackbody radiation - Measurement of the lifetime of metastable CO Using the low energy: - Collision experiments Science 313, 1617 (2006) - Reflection of OH molecules by a magnetic mirror NJP 10, (2008) - Dipole-dipole interactions, ultracold collisions - Towards a higher phase space density: Magnetic trapping and accumulation of NH molecules

The effect of blackbody radiation on trapped polar molecules Goal of the experiment: Demonstrate the effect of BBR on neutral polar molecules by exploiting the difference between OH and OD Goal of the experiment: Demonstrate the effect of BBR on neutral polar molecules by exploiting the difference between OH and OD

The Experimental setup

Controlling the velocity of OH molecules using the Stark decelerator

OH and OD have similar stark shifts, can even be decelerated and trapped together The slow molecules are brought to a standstill at the center of an electrostatic trap, then the trap is switched on 7 kV -15 kV 15 kV -15 kV 15 kV

Room temperature blackbody radiation spectrum Room temperature blackbody radiation spectrum All decelerated molecules are initially in the J=3/2, f state.

Losses due to 1. background gas* 0.17 s blackbody radiation OH: 0.36 s -1 OD: 0.14 s -1 * Joop J. Gilijamse, Steven Hoekstra, Sebastiaan Y. T. van de Meerakker, Gerrit C. Groenenboom, Gerard Meijer, Science,313,1617 (2006)

Conclusion: Optical pumping by blackbody radiation is a feature shared by all polar molecules and fundamentally limits the time that these molecules can be kept in a single quantum state in a trap. Steven Hoekstra, Joop J. Gilijamse, Boris Sartakov, Nicolas Vanhaecke, Ludwig Scharfenberg, Sebastiaan Y. T. van de Meerakker, and Gerard Meijer, PRL98, (2007)

The radiative lifetime of metastable CO (a 3 π, v=0) Decelerate and trap CO (a 3 π), then directly measure the radiative lifetime by observing trap decay  Σ τ~3 ms

Time-of-flight profile of the trapping of a decaying molecule:

a 3  1, v=0, J=1 : 2.63 ± 0.03 ms a 3  2, v=0, J=2 : 143 ± 4 ms ratio of the lifetimes: 54.4 ± 1.6 known ratio from spectroscopy: ± 0.01 Conclusion: the radiative lifetime of metastable CO ( a 3 π ) has been measured with unprecedented precision by deceleration and trapping Joop J. Gilijamse, Steven Hoekstra, Samuel A. Meek, Markus Metsala, Sebastiaan Y. T. van de Meerakker, Gerard Meijer and GerritC.Groenenboom, JCP127, (2007)

Introduction and Motivation: What to do with Stark-decelerated and trapped polar molecules Using the long interaction time: - High precision measurements / spectroscopy - Understanding trap loss mechanisms: Blackbody radiation - Measurement of the lifetime of metastable CO JCP127, (2007) Using the low energy: - Collision experiments Science 313, 1617 (2006) - Reflection of OH molecules by a magnetic mirror NJP 10, (2008) - Dipole-dipole interactions, ultracold collisions - Towards a higher phase space density: Magnetic trapping and accumulation of NH molecules PRL98, (2007)

NH trapping and accumulation in a magnetic trap Current densities: cm -3 Current temperatures: mK (~ cm -1 ) Current trapping times: a few seconds (BBR &backgr.gas) Experiment repetition rate: 10 Hz Increase of phase-space density by simply reloading the next decelerated packet of molecules into the trap is impossible due to Liouville’s Theorem…

Groundstate Metastable state (  of a few seconds) neglible Stark shift Stark 100 kV/cm: 1.67 cm -1 produced in a supersonic expansion by photolysis of HN 3 can be decelerated using Stark decelerator and trapped electrostatically v=0, j=2 v=0, j=1 The NH molecule - Excitation: 584 nm Background free detection: 336 nm  ~ 450 ns

Deceleration of metastable NH

Electrostatic trapping of metastable NH Lower limit for the radiative life time of the NH(a 1 ,v’=0,J‘=2) :  ≥ 2.7 seconds S. Hoekstra et al, Phys. Rev. A (2007) The slow molecules are brought to a standstill at the center of an electrostatic trap, then the trap is switched on 7 kV -15 kV 15 kV -15 kV 15 kV

Groundstate Metastable state (  > 2.7 seconds) Back to the NH molecule … Stark Deceleration and trapping …. but Zeeman shift! (10 Hz) Magnetic trap, continuously on, accumulates cold molecules, increases phase-space density Excitation: 584 nm Detection: 336 nm  ~ 450 ns Cold source of groundstate NH, with negligible Stark shift … also has a Zeeman shift …

Accumulation of groundstate NH Magnetic trapping: 2x16 windings, anti-hemholz, 1000 Ampere, 28 kW cooling power Gauss/cm Deceleration: special electrodes for improved deceleration from 150 m/s to standstill, that fit inside a magnetic trap Transfer laser: 60 mJ pulsed 584 nm from RDL-PDA combination or cwlaser using a power-build-up cavity

Magnetically trapped NH (a 1  ) Metastable NH molecules are very efficiently stopped using new electrodes Magnetically trapped metastable NH molecules Not all stopped molecules are trapped: - expect 50% max - trap only 7 mK deep for metastable molecules! Currently working on detection of trapped groundstate NH molecules

Blackbody radiation Metastable CO lifetime Magnetic trapping of NH (a 1  ) Conclusions

Bas v/dMeerakker Bas v/dMeerakker Joop Gilijamse Joop Gilijamse Peter Zieger Peter Zieger Gerard Meijer Gerard Meijer Ludwig Scharfenberg Ludwig Scharfenberg Markus Metsala Markus Metsala Technical support: Sandy Gewinner, HenrikHaak Theoretical support: Boris Sartakov, GerritGroenenboom Steven Hoekstra Steven Hoekstra BBR: Nicolas Vanhaecke CO: Samuel Meek