nanosurface 2007-11-23 04:24
PhD studentship: Precision Measurements on Cold Molecules in a Fountain
At Laser Centre Vrije Universiteit Amsterdam, Atomic, Molecular and Laser Physics Group
Field(s): molecular physics
Application deadline: Jan 09 (Wed), 2008
Submitted: Nov 09, 2007
Contact: Hendrick L. Bethlem
E-mail: [email]rick@few.vu.nl[/email]
Phone: 0031 20 598 7951
Address: Laser Centre Vrije Universiteit, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands
Job description: The ability to manipulate neutral molecules using inhomogeneous electric fields offers new possibilities for precision measurements. At LCVU, we are building a molecular fountain. In this fountain, the first of its kind, polar molecules are decelerated, cooled, and subsequently launched upwards some 10-50 cm before falling back under gravity, thereby passing a microwave cavity or laser beam twice – as they fly up and as they fall back down. The effective interrogation time in such a Ramsey type measurement scheme includes the entire flight time between the two traversals through the driving field, which can be up to a second. This long interrogation time will allow for extreme precision measurements on molecular structure to a level at which fundamental physics theories can be tested.
We plan to use the inversion frequency in ammonia around 23 GHz as a test case. This measurement may be used as a test of the time-variation of fundamental constants – an issue that has profound implications on how we understand the universe. The inversion frequency in ammonia is determined by the tunneling rate of the protons through the barrier between the two equivalent configurations of the molecule, and is exponentially dependent on the proton mass. By monitoring the inversion frequency over a period of a few years, a possible variation of the proton-electron mass ratio can be constrained or measured.
The vertical molecular beam decelerator for producing a slow beam of ammonia is fully operational. We are currently implementing an electric quadrupole lens system to focus the beam into the microwave cavity. The successful applicant will test and optimize this system and will perform first measurements on molecules in the fountain.
The PhD student may start immediately, and will be funded for four years.