Improved Electron Electric-Dipole-Moment Measurement
(a) Schematic of the measurement apparatus used in the present work. The initial state can be populated using either (b) an optical pumping scheme similar to that used in ACME I, or (c) a STIRAP scheme.* [Reprinted with permission from APS]
Experimental searches for the electron electric-dipole moment (EDM) probe new physics beyond the standard model. The current best EDM limit was set by the ACME Collaboration, constraining time-reversal symmetry (T) violating physics at the TeV energy scale. ACME used optical pumping to prepare a coherent superposition of ThO H3 Δ1 states that have aligned electron spins. Spin precession due to the molecule's internal electric field was measured to extract the EDM.
In a new Physical Review A paper, grad student Cristian Panda and Jacob Baron, research scholars Adam West, and a group of colleagues from Harvard and Yale led by Profs. John Doyle and Gerald Gabrielse, report on their improved method for preparing the spin-aligned state of the electron by using stimulated Raman adiabatic passage (STIRAP). The authors demonstrate a transfer efficiency of 75 ± 5%, representing a significant gain in signal for a next-generation EDM experiment. Furthermore, they discuss the particularities of implementing STIRAP in systems such as theirs, where molecular ensembles with large phase-space distributions are transferred via weak molecular transitions with limited laser power and limited optical access.
*See C. D. Panda, B. R. O'Leary, A. D. West, J. Baron, P. W. Hess, C. Hoffman, E. Kirilov, C. B. Overstreet, E. P. West, D. DeMille, J. M. Doyle, and G. Gabrielse, "Stimulated Raman adiabatic passage preparation of a coherent superposition of ThO H3 Δ1 states for an improved electron electric-dipole-moment measurement," Phys. Rev. A 93, 052110 (16 May 2016) DOI:http://dx.doi.org/10.1103/PhysRevA.93.052110.