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Hess, P

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Hess, P
Author's Publications: search.filters.isAuthorOfPublication.8d8a198c-b39d-4d0c-a8ab-705032907a0d

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    Stimulated Raman Adiabatic Passage Preparation of a Coherent Superposition of ThO H3Δ1 States for an Improved Electron Electric-Dipole-Moment Measurement
    (American Physical Society (APS), 2016) Panda, Cristian; O, B. R.; West, A. D.; Baron, J.; Hess, P; Hoffman, C.; Kirilov, E; Overstreet, C. B.; West, Elizabeth Petrik; DeMille, D.; Doyle, John; Gabrielse, Gerald
    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 [Science 343, 269 (2014), 10.1126/science.1248213], constraining time-reversal symmetry (T ) violating physics at the TeV energy scale. ACME used optical pumping to prepare a coherent superposition of ThO H3Δ1 states that have aligned electron spins. Spin precession due to the molecule's internal electric field was measured to extract the EDM. We report here on an improved method for preparing this spin-aligned state of the electron by using stimulated Raman adiabatic passage (STIRAP). We demonstrate a transfer efficiency of 75 %±5 % , representing a significant gain in signal for a next-generation EDM experiment. We discuss the particularities of implementing STIRAP in systems such as ours, where molecular ensembles with large phase-space distributions are transferred via weak molecular transitions with limited laser power and limited optical access.
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    Improving the Limit on the Electron EDM: Data Acquisition and Systematics Studies in the ACME Experiment
    (2014-06-06) Hess, P; Gabrielse, Gerald; Morii, Masahiro; Lukin, Mikhail
    The ACME collaboration has completed a measurement setting a new upper limit on the size of the electron's permanent electric dipole moment (EDM). The existence of the EDM is well motivated by theories extending the standard model of particle physics, with predicted sizes very close to the current experimental limit. The new limit was set by measuring spin precession within the metastable H state of the polar molecule thorium monoxide (ThO). A particular focus here is on the automated data acquisition system developed to search for a precession phase odd under internal and external reversal of the electric field. Automated switching of many different experimental controls allowed a rapid diagnosis of major systematics, including the dominant systematic caused by non-reversing electric fields and laser polarization gradients. Polarimetry measurements made it possible to quantify and minimize the polarization gradients in our state preparation and probe lasers. Three separate measurements were used to determine the electric field that did not reverse when we tried to switch the field direction. The new bound of |de|< 8.7 × 10-29 e cm is over an order of magnitude smaller than previous limits, and strongly limits T-violating physics at TeV energy scales.
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    A Cryogenic Beam of Refractory, Chemically Reactive Molecules with Expansion Cooling
    (Royal Society of Chemistry, 2011) Hutzler, Nicholas; Parsons, Maxwell Fredrick; Gurevich, Yulia Vsevolodovna; Hess, P; West, Elizabeth Petrik; Spaun, Ben; Vutha, Amar; DeMille, David; Gabrielse, Gerald; Doyle, John
    Cryogenically cooled buffer gas beam sources of the molecule thorium monoxide (ThO) are optimized and characterized. Both helium and neon buffer gas sources are shown to produce ThO beams with high flux, low divergence, low forward velocity, and cold internal temperature for a variety of stagnation densities and nozzle diameters. The beam operates with a buffer gas stagnation density of \(\sim 10^{15}-10^{16}\) cm\(^{-3}\) (Reynolds number \(\sim 1-100\)), resulting in expansion cooling of the internal temperature of the ThO to as low as 2 K. For the neon (helium) based source, this represents cooling by a factor of about 10 (2) from the initial nozzle temperature of about 20 K (4 K). These sources deliver \(\sim 10^{11}\) ThO molecules in a single quantum state within a 1-3 ms long pulse at 10 Hz repetition rate. Under conditions optimized for a future precision spectroscopy application [A C Vutha et al 2010 J. Phys. B: At. Mol. Opt. Phys. 43 074007], the neon-based beam has the following characteristics: forward velocity of 170 m/s, internal temperature of 3.4 K, and brightness of \(3 \times 10^{11}\) ground state molecules per steradian per pulse. Compared to typical supersonic sources, the relatively low stagnation density of this source, and the fact that the cooling mechanism relies only on collisions with an inert buffer gas, make it widely applicable to many atomic and molecular species, including those which are chemically reactive, such as ThO.