Experimental measurements of the validity of the discrete symmetries parity P (inversion of the spatial coordinates), time reversal T and charge conjugation C (exchange of particle and antiparticle) are powerful tools to test fundamental theories like the Standard Model (SM) of the electro weak interactions. Particularly sensitive are searches for violations of one or more of the symmetries C, P and T. Many experiments are underway worldwide. Objects like permanent electric dipole moments (EDMs) of a fundamental particle, which can e.g. arise from a spatial separation of positive and negative charges in an object (Fig. a), would violate the symmetries P and T at the same time. Thus experimental searches for a nonzero EDM are provide unique input to the theoretical model building in nature. Almost all extensions to the SM include partially broken symmetries and consequently lead to EDMs. Fundamental EDMs can experimence large amplifications in larger systems like nuclei, atoms or molecules. An EDM results in a linear shift of the energy levels in an electric field. Such shifts can be measured by precision frequency measurements using atomic physics methods. A search for a nonzero EDM requires the choice of a sensitive system. We have chosen the neutral heavy alkaline earth element radium (Ra). Its unique sensitive towards an EDM arise from its nuclear and atomic properties, which lead to largest enhancement factors of the underlying EDM in atomic systems. The Ra isotopes of interest are short lived (225Ra, half-life 14.8 d; 213Ra, half-life 2.74 min) but they are available at the TRImP facility at KVI. Precision laser spectroscopy of radium isotopes is required to fully exploit the sensitivity of the system for an EDM measurement. Here the lifetimes of excited meatstable states and the hyperfine structure splitting are required as input for atomic structure calculations. These measurements are done on a weak atomic beam of 225Ra (link to subpage with info on the experiment). This spectroscopy provides also precision determination of the transitionfrequencies in Ra, which are needed for the development of an "efficient laser cooling and trapping scheme" for Ra. In a further stage trapped Ra atoms will be transfered into an optical dipole trap.
Laser Cooling and trapping of heavy alkaline earth elements
Laser cooling and trapping of the heavy alkaline earth elements Ba and Ra suffer from the absence of a strong closed transition for laser cooling. The strongest transitions whic can be used for laser cooling in these systems are ns2 1S0 - nsnp 1P1 with n=6 for Ba and n=7 for Ra. The excitedstate of this transition have a branching of about 0.3% to long lifed metastable D states.Several additional lasers are required for transfering the the atoms back into the main coolingtransition. To successfully laser cool Ba and collect atoms in a magneto optical trap (MOT) weutilized seven lasers simultaneously (S. De, U. Dammalapati, K. Jungmann, L. Willmann, PRA RapidComm. 041402 (2009)). This setup had a capture efficiency from an atomic beam of 1% and morepowerful lasers would allow to increase this efficiency.
|Last modified:||20 June 2014 10.19 a.m.|