Toward a Determination of the Proton-Electron Mass Ratio from the Lamb-Dip Measurement of HD.

Precision spectroscopy of the hydrogen molecule is a test ground of quantum electrodynamics (QED), and it may serve for the determination of fundamental constants. Using a comb-locked cavity ring-down spectrometer, for the first time, we observed the Lamb-dip spectrum of the R(1) line in the overtone of hydrogen deuteride (HD). The line position was determined to be 217 105 182.79±0.03_{stat}±0.08_{syst} MHz (δν/ν=4×10^{-10}), which is the most accurate rovibrational transition ever measured in the ground electronic state of molecular hydrogen. Moreover, from calculations including QED effects up to the order m_{e}α^{6}, we obtained predictions for this R(1) line as well as for the HD dissociation energy, which are less accurate but signaling the importance of the complete treatment of nonadiabatic effects. Provided that the theoretical calculation reaches the same accuracy, the present measurement will lead to a determination of the proton-to-electron mass ratio with a precision of 1.3 parts per billion.

Laser Spectroscopy of the Fine-Structure Splitting in the 2

The fine-structure splitting in the 2^{3}P_{J} (J=0, 1, 2) levels of ^{4}He is of great interest for tests of quantum electrodynamics and for the determination of the fine-structure constant α. The 2^{3}P_{0}-2^{3}P_{2} and 2^{3}P_{1}-2^{3}P_{2} intervals are measured by laser spectroscopy of the ^{3}P_{J}-2^{3}S_{1} transitions at 1083 nm in an atomic beam, and are determined to be 31 908 130.98±0.13 kHz and 2 291 177.56±0.19 kHz, respectively. Compared with calculations, which include terms up to α^{5}Ry, the deviation for the α-sensitive interval 2^{3}P_{0}-2^{3}P_{2} is only 0.22 kHz. It opens the window for further improvement of theoretical predictions and an independent determination of the fine-structure constant α with a precision of 2×10^{-9}.

Measurement of the Frequency of the 2

The 2 ^{3}S-2 ^{3}P transition of ^{4}He was measured by comb-linked laser spectroscopy using a transverse-cooled atomic beam. The centroid frequency was determined to be 276 736 495 600.0(1.4) kHz, with a fractional uncertainty of 5.1×10^{-12}. This value is not only more accurate but also differs by as much as -49.5 kHz (20σ) from the previous result given by [Cancio Pastor et al., Phys. Rev. Lett. 92, 023001 (2004)PRLTAO0031-900710.1103/PhysRevLett.92.023001; Cancio Pastor et al.Phys. Rev. Lett.97, 139903(E) (2006)10.1103/PhysRevLett.97.139903; Cancio Pastor et al.Phys. Rev. Lett.108, 143001 (2012)10.1103/PhysRevLett.108.143001]. In combination with ongoing theoretical calculations, this work may allow the most accurate determination of the nuclear charge radius of helium.

One-loop dominance in the imaginary part of the polarizability: application to blackbody and noncontact van der Waals friction.

Phenomenologically important quantum dissipative processes include blackbody friction (an atom absorbs counterpropagating blueshifted photons and spontaneously emits them in all directions, losing kinetic energy) and noncontact van der Waals friction (in the vicinity of a dielectric surface, the mirror charges of the constituent particles inside the surface experience drag, slowing the atom). The theoretical predictions for these processes are modified upon a rigorous quantum electrodynamic treatment, which shows that the one-loop "correction" yields the dominant contribution to the off-resonant, gauge-invariant, imaginary part of the atom's polarizability at room temperature, for typical atom-surface interactions. The tree-level contribution to the polarizability dominates at high temperature.

Fundamental vibration of molecular hydrogen.

The fundamental ground tone vibration of H(2), HD, and D(2) is determined to an accuracy of 2×10(-4) cm(-1) from Doppler-free laser spectroscopy in the collisionless environment of a molecular beam. This rotationless vibrational splitting is derived from the combination difference between electronic excitation from the X(1)Σ(g)(+), v=0, and v=1 levels to a common EF(1)Σ(g)(+), v=0 level. Agreement within 1σ between the experimental result and a full ab initio calculation provides a stringent test of quantum electrodynamics in a chemically bound system.

Frequency metrology of helium around 1083 nm and determination of the nuclear charge radius.

We measure the absolute frequency of seven out of the nine allowed transitions between the 2 (3)S and 2 (3)P hyperfine manifolds in a metastable (3)He beam by using an optical frequency comb synthesizer-assisted spectrometer. The relative uncertainty of our measurements ranges from 1×10(-11) to 5×10(-12), which is, to our knowledge, the most precise result for any optical ^{3}He transition to date. The resulting 2 (3)P-2 (3)S centroid frequency is 276,702,827,204.8(2.4) kHz. Comparing this value with the known result for the (4)He centroid and performing ab initio QED calculations of the (4)He-(3)He isotope shift, we extract the difference of the squared nuclear charge radii δr(2) of (3)He and (4)He. Our result for δr(2)=1.074(3) fm(2) disagrees by about 4σ with the recent determination [R. van Rooij et al., Science 333, 196 (2011)].

QED theory of the nuclear magnetic shielding in hydrogenlike ions.

The shielding of the nuclear magnetic moment by the bound electron in hydrogenlike ions is calculated ab initio with inclusion of relativistic, nuclear, and quantum electrodynamics (QED) effects. The QED correction is evaluated to all orders in the nuclear binding strength parameter and, independently, to the first order in the expansion in this parameter. The results obtained lay the basis for the high-precision determination of nuclear magnetic dipole moments from measurements of the g factor of hydrogenlike ions.

Isotope shift of the 32S 1/2 -22S 1/2 transition in lithium and the nuclear polarizability.

High precision calculation of the isotope shift of the 3(2)S(1/2)-2(2)S(1/2) transition in lithium is presented. The wave function and matrix elements of relativistic operators are obtained by using recursion relations. Apart from the relativistic contribution, we obtain the nuclear polarizability correction for 11Li. The resulting difference of the squared charge radii 11Li-7Li based on the measurements of Sánchez et al. [Phys. Rev. Lett. 96, 033002 (2006)10.1103/PhysRevLett.96.033002] is deltar(ch)(2)=0.157(81) fm(2), which significantly differs from the previous evaluation.

QED corrections to the parity-nonconserving 6s-7s amplitude in 133Cs.

The complete gauge-invariant set of the one-loop QED corrections to the parity-nonconserving 6s-7s amplitude in 133Cs is evaluated to all orders in alphaZ using a local version of the Dirac-Hartree-Fock potential. The calculations are performed in both length and velocity gauges for the absorbed photon. The total binding QED correction is found to be -0.27(3)%. The weak charge of 133Cs, derived using two most accurate values of the vector transition polarizability beta, is Q(W)=-72.57(46) for beta=26.957(51)a(3)(B) and Q(W)=-73.09(54) for beta=27.15(11)a(3)(B). The first value deviates by 1.1sigma from the prediction of the standard model, while the second one is in perfect agreement with it.

Improved result for helium 2(3)S1 ionization energy

A complete calculation of relativistic and quantum electrodynamic effects to order malpha(6) on the energy of the 2(3)S1 state in helium is presented. The result, beyond the previously known radiative corrections, amounts to -3.00(1) MHz, and significantly reduces the theoretical uncertainty. The improved theoretical predictions are compared to the best available experimental result for the 2(3)S1 state.