Two-photon spectroscopy of trapped HD+^+ ions in the Lamb-Dicke regime

We study the feasibility of nearly-degenerate two-photon rovibrational spectroscopy in ensembles of trapped, sympathetically cooled hydrogen molecular ions using a resonance-enhanced multiphoton dissociation (REMPD) scheme. Taking advantage of quasi-coincidences in the rovibrational spectrum, the excitation lasers are tuned close to an intermediate level to resonantly enhance two-photon absorption. Realistic simulations of the REMPD signal are obtained using a four-level model that takes into account saturation effects, ion trajectories, laser frequency noise and redistribution of population by blackbody radiation. We show that the use of counterpropagating laser beams enables optical excitation in an effective Lamb-Dicke regime. Sub-Doppler lines having widths in the 100 Hz range can be observed with good signal-to-noise ratio for an optimal choice of laser detunings. Our results indicate the feasibility of molecular spectroscopy at the $10^{-14}$ accuracy level for improved tests of molecular QED, a new determination of the proton-to-electron mass ratio, and studies of the time (in)dependence of the latter.Comment: 16 pages, 17 figure

Direct frequency-comb spectroscopy of a dipole-forbidden clock transition in trapped 40Ca+ ions

We demonstrate direct frequency-comb (FC) spectroscopy of the dipole-forbidden 4

Extraction of spin-averaged rovibrational transition frequencies in HD+^+ for the determination of fundamental constants

We present a comprehensive analysis of all currently available high-accuracy frequency measurements of rotational and rovibrational transitions in the hydrogen molecular ion HD$^+$. Our analysis utilises the theoretically calculated hyperfine structure to extract the values of three spin-averaged transition frequencies through a global linear least-squares adjustment that takes into account theory-induced correlations between the different transitions. We subsequently use the three spin-averaged transition frequencies as input data in a second adjustment which employs precise theoretical expressions for the transition frequencies, written as a function of the proton, deuteron and electron relative atomic masses, the Rydberg constant, and the proton and deuteron charge radii. Our analysis shows that the HD$^+$ data may significantly improve the value of the electron relative atomic mass and the proton-electron mass ratio, in particular if combined with recent high-precision measurements of particle atomic masses and mass ratios obtained from Penning traps.Comment: 19 pages, 2 figures, 9 table

Hydrogen molecular ions: New schemes for metrology and fundamental physics tests

High-accuracy spectroscopy of hydrogen molecular ions has important applications for the metrology of fundamental constants and tests of fundamental theories. Up to now, the experimental resolution has not surpassed the part-per-billion range. We discuss two methods by which it could be improved by a huge factor. Firstly, the feasibility of Doppler-free quasidegenerate two-photon spectroscopy of trapped and sympathetically cooled ensembles of HD+ ions is discussed, and it is shown that rovibrational transitions may be detected with a good signal-to-noise ratio. Secondly, the performance of a molecular quantum-logic ion clock based on a single Be+-H2 + ion pair is analyzed in detail. Such a clock could allow testing the constancy of the proton-to-electron mass ratio at the 10-17/yr level

DETERMINATION OF THE IONIZATION AND DISSOCIATION ENERGIES OF MOLECULAR HYDROGEN, H2_2

Author Institution: Laboratorium fur Physikalische Chemie, ETH-Zurich, 8093; Zurich, Switzerland; Laser Centre, Department of Physics and Astronomy, Vrije; Universiteit, De Boelelaan 1081, 1081 HV Amsterdam, The NetherlandsThe transition wave number from the $EF$ $^1\Sigma _g^+$($v=0,N=1$) energy level of ortho-H$_2$ to the 54$p1_1(0)$ Rydberg state below the $X^{+}$ $^2\Sigma^+_g$($v^+=0,N^+=1$) ground state of ortho-H$^+_2$ has been measured to be 25209.99756$\pm$(0.00022)$_{\rm statistical}$$\pm$(0.00007)$_{\rm systematic}$~cm$^{-1}$. Combining this result with previous experimental and theoretical results for other energy level intervals, the ionization and dissociation energies of the hydrogen molecule have been determined to be 124417.49113(37) cm$^{-1}$ and 36118.06962(37) cm$^{-1}$, respectively, which represents a precision improvement over previous experimental and theoretical results by more than one order of magnitude. The new value of the ionization energy can be regarded as the most precise and accurate experimental result of this quantity, whereas the dissociation energy is a hybrid experimental-theoretical determination

Determination of the ionization and dissociation energies of the hydrogen molecule

The transition wave number from the EF (1)Sigma(+)(g)(v=0,N=1) energy level of ortho-H-2 to the 54p1(1)(0) Rydberg state below the X+ (2)Sigma(+)(g)(v(+)=0,N+=1) ground state of ortho-H-2(+) has been measured to be 25 209.997 56 +/-(0.000 22)(statistical)+/-(0.000 07)(systematic) cm(-1). Combining this result with previous experimental and theoretical results for other energy level intervals, the ionization and dissociation energies of the hydrogen molecule have been determined to be 124 417.491 13(37) and 36 118.069 62(37) cm(-1), respectively, which represents a precision improvement over previous experimental and theoretical results by more than one order of magnitude. The new value of the ionization energy can be regarded as the most precise and accurate experimental result of this quantity, whereas the dissociation energy is a hybrid experimental-theoretical determination

Direct frequency comb spectroscopy in trapped 40Ca+ ions on a dipoleforbidden clock transition

Optical frequency combs (FCs) have revolutionised ultra-high precision metrology by providing a link between optical and microwave frequencies [1]. While FCs are traditionally used for calibrating a CW probe-laser, also direct frequency comb spectroscopy (DFCS) is possible. We have recently demonstrated the versatility of DFCS performed in the environment of an ion trap, combining the broad spectral range of a Ti:sapphire FC with the feasibility of trapping and (sympathetic) cooling of different ion species [2]