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arXiv:1305.2179 · Physical Review A

Shot-noise-limited spin measurements in a pulsed molecular beam

Emil Kirilov, Wesley C. Campbell, John M. Doyle, G. Gabrielse, Yulia V. Gurevich, Paul Hess, Nicholas R. Hutzler, Brendon O'Leary, Elizabeth Petrik, B. Spaun, Amar C. Vutha, David P. DeMille

Published Jul 26, 2013• 28 citations
arXivHTMLPDF

Abstract

Heavy diatomic molecules have been identified as good candidates for use in electron electric dipole moment (eEDM) searches. Suitable molecular species can be produced in pulsed beams, but with a total flux and/or temporal evolution that varies significantly from pulse to pulse. These variations can degrade the experimental sensitivity to changes in the spin precession phase of an electrically polarized state, which is the observable of interest for an eEDM measurement. We present two methods for measurement of the phase that provide immunity to beam temporal variations, and make it possible to reach shot-noise-limited sensitivity. Each method employs rapid projection of the spin state onto both components of an orthonormal basis. We demonstrate both methods using the eEDM-sensitive $H{\phantom{\rule{0.16em}{0ex}}}^{3}{\ensuremath{\Delta}}_{1}$ state of thorium monoxide, and use one of them to measure the magnetic moment of this state with increased accuracy relative to previous determinations.

DOI
10.1103/physreva.88.013844

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Abstract Measurements of the electron’s electric dipole moment (eEDM) are demanding tests of physics beyond the standard model. We describe how ultracold YbF molecules could be used to improve the precision of eEDM measurements by two to three orders of magnitude. Using numerical simulations, we show how the combination of magnetic focussing, two-dimensional transverse laser cooling, and frequency-chirped laser slowing, can produce an intense, slow, highly-collimated molecular beam. We show how to make a magneto-optical trap of YbF molecules and how the molecules could be loaded into an optical lattice. eEDM measurements could be made using the slow molecular beam or using molecules trapped in the lattice. We estimate the statistical sensitivity that could be reached in each case and consider how sources of noise can be reduced so that the shot-noise limit of sensitivity can be reached. We also consider systematic effects due to magnetic fields and vector light shifts and how they could be controlled.
Abstract The electric dipole moment of the electron (eEDM) can be measured with high precision using heavy polar molecules. In this paper, we report on a series of new techniques that have improved the statistical sensitivity of the YbF eEDM experiment. We increase the number of molecules participating in the experiment by an order of magnitude using a carefully designed optical pumping scheme. We also increase the detection efficiency of these molecules by another order of magnitude using an optical cycling scheme. In addition, we show how to destabilise dark states and reduce backgrounds that otherwise limit the efficiency of these techniques. Together, these improvements allow us to demonstrate a statistical sensitivity of 1.8 × 10 −28 e cm after one day of measurement, which is 1.2 times the shot-noise limit. The techniques presented here are applicable to other high-precision measurements using molecules.
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We present the conceptual design of an experiment to measure the electron's electric dipole moment (eEDM) using 138^{138}138BaOH molecules in an optical lattice. The BaOH molecule is laser-coolable and highly sensitive to the eEDM, making it an attractive candidate for such a precision measurement, and capturing it in an optical lattice offers potentially very long coherence times. We study possibilities and limitations of this approach, identify the most crucial limiting factors and ways to overcome them. The proposed apparatus can reach a statistical error of 10−30 e 10^{-30}\,e\,10−30ecm by measuring spin precession on a total number of 5×1095 \times 10^95×109 molecules over a span of 120 days.
Abstract The current best upper limit for electron electric dipole moment (EDM), |d e| < 1.1 × 10−29 e cm (90% confidence), was set by the ACME Collaboration in 2018. The ACME experiment uses a spin-precession measurement in a cold beam of thorium monoxide (ThO) molecules to detect d e. An improvement in statistical uncertainty would be possible with more efficient use of molecules from the cryogenic buffer gas beam source. Here, we demonstrate electrostatic focusing of the ThO beam with a hexapole lens. This results in a factor of 16 enhancement in the molecular flux detectable downstream, in a beamline similar to that built for the next generation of ACME. We also demonstrate an upgraded rotational cooling scheme that increases the ground state population by 3.5 times compared to no cooling, consistent with expectations and a factor of 1.4 larger than previously in ACME. When combined with other demonstrated improvements, we project over an order of magnitude improvement in statistical sensitivity for the next generation ACME electron EDM search.
Cold molecules provide an excellent platform for quantum information, cold chemistry, and precision measurement. Certain molecules have enhanced sensitivity to beyond standard model physics, such as the electron's electric dipole moment (eEDM). Molecular ions are easily trappable and are therefore particularly attractive for precision measurements where sensitivity scales with interrogation time. Here, we demonstrate a spin precession measurement with second-scale coherence at the quantum projection noise (QPN) limit with hundreds of trapped molecular ions, chosen for their sensitivity to the eEDM rather than their amenability to state control and readout. Orientation-resolved resonant photodissociation allows us to simultaneously measure two quantum states with opposite eEDM sensitivity, reaching the QPN limit and fully exploiting the high count rate and long coherence.