arXiv subjects

John J. McFerran

Publications and source records attributed to John J. McFerran.

11 recordsLinked to original sources

arXiv2023

Intercombination line frequencies in $^{171}$Yb validated with the clock transition

We have carried absolute frequency measurements of the $(6s^{2})\,^{1}S_{0}$ $-$ $(6s6p)\,^{3}P_{1}$ transition in $^{171}$Yb (the intercombination line), where the spin-1/2 isotope yields two hyperfine lines. The measurements rely on sub-Doppler spectroscopy to yield a discriminator to which a 556 nm laser is locked. The frequency reference for the optical frequency measurements is a high-quality quartz oscillator steered to the GNSS timescale that is bridged with a frequency comb. The reference is validated to $\sim3\times10^{-12}$ by spectroscopy on the $^{1}S_{0}-\,^{3}P_{0}$ (clock) line in laser cooled and trapped $^{171}$Yb atoms. From the hyperfine separation between the $F=1/2$ and $F=3/2$ levels of $^{3}P_{1}$ we determine the hyperfine constant to be $A(^3P_1)= 3\,957\,833\,(28)$ kHz.

physics.atom-ph↗

arXiv2021

MCDHF-CI calculations for Hg and Cd with estimates for unknown clock transition frequencies

By use of the \textsc{grasp2018} package we perform Multiconfiguration Dirac-Hartree-Fock (MCDHF) calculations with configuration interaction (CI) for the $^{1}S_{0}$ and $^{3}P_{0,1}^o$ levels in neutral cadmium and mercury. By supplying the resultant atomic state functions to the \textsc{ris4} program, we evaluate the mass and field shift parameters for the $^{1}S_{0}-\,^{3}P_{0}^o$ (clock) and $^{1}S_{0}-\,^{3}P_{1}^o$ (intercombination) lines. We make revised estimates of the nuclear charge parameters $λ^{A,A'}$ and differences in mean-square charge radii $δ\langle r^2\rangle^{A,A'}$ for both elements and point out a discrepancy with tabulated data for Cd. In constructing a King plot with the Hg lines we examine the second-order hyperfine interaction for the $^{3}P_{0,1}^o$ levels. Isotope shifts for the clock transition have been estimated from which we predict the unknown clock line frequencies in the bosonic Hg isotopes and all the naturally occurring isotopes of Cd.

physics.atom-ph↗

arXiv2021

Isotope shifts for ${}^1S_0-{}^3P_{0,1}^o$ Yb lines from multi-configuration Dirac-Hartree-Fock calculations

Relativistic multiconfiguration Dirac-Hartree-Fock (MCDHF) calculations with configuration interaction (CI) are carried out for the $^{1}S_{0}$ and $^{3}P_{0,1}^o$ states in neutral ytterbium by use of the available GRASP2018 package. From the resultant atomic state functions and the RIS4 extension, we evaluate the mass and field shift parameters for the $^{1}S_{0}-\,^{3}P_{0}^o$ (clock) and $^{1}S_{0}-\,^{3}P_{1}^o$ (intercombination) lines. We present improved estimates of the nuclear charge parameters, $λ^{A,A'}$, and differences in mean-square charge radii, $δ\langle r^2\rangle^{A,A'}$, and examine the second-order hyperfine interaction for the $^{3}P_{0,1}^o$ states. Isotope shifts for the clock transition have been estimated by three largely independent means from which we predict the unknown clock line frequencies in bosonic Yb isotopes. Knowledge of these line frequencies has implications for King plot nonlinearity tests and the search for beyond Standard-Model signatures.

physics.atom-ph↗

arXiv2020

Simulation of optical lattice trap loading from a cold atomic ensemble

We model the efficiency of loading atoms of various species into a one dimensional optical lattice from a cold ensemble taking into account the initial cloud temperature and size, the lattice laser properties affecting the trapping potential, and atomic parameters. Stochastic sampling and dynamical evolution are used to simulate the transfer, leading to estimates of transfer efficiency for varying trap depth and profile. Tracing the motion of the atoms also enables the evaluation of the equilibrium temperature and site occupancy in the lattice. The simulation compares favourably against a number of experimental results, and is used to compute an optimum lattice-waist to cloud-radius ratio for a given optical power.

physics.atom-ph↗

arXiv2020

Fourier transform detection of weak optical transitions with cyclic routines

We demonstrate a means of detecting weak optical transitions in cold atoms that undergo cyclic routines with high sensitivity. The gain in sensitivity is made by probing atoms on alternate cycles leading to a regular modulation of the ground state atom population when at the resonance frequency. The atomic transition is identified by conducting a fast Fourier transform via algorithm or instrument. We find an enhancement of detection sensitivity compared to more conventional scanning methods of $\sim 20$ for the same sampling time, and can detect clock lines with fewer than $10^3$ atoms in a magneto-optical trap. We apply the method to the $(6s^{2})$ $ ^{1}S_{0} - (6s6p)$ $^{3}P_{0}$ clock transition in $^{171}$Yb and $^{173}$Yb. The ac-Stark shift of this line in $^{171}$Yb is measured to be 0.19(3) kHz$\cdot$W$^{-1}\cdot$m$^2$ at 556 nm.

physics.atom-ph↗

arXiv2019

Hyperfine constants and line separations for the $^{1}S_{0}-\,^{3}P_{1}$ intercombination line in neutral ytterbium with sub-Doppler resolution

Optical frequency measurements of the intercombination line $(6s^{2})\,^{1}S_{0} -(6s6p)\,^{3}P_{1}$ in the isotopes of ytterbium are carried out with the use of sub-Doppler fluorescence spectroscopy on an atomic beam. A dispersive signal is generated to which a master laser is locked, while frequency counting of an auxiliary beat signal is performed via a frequency comb referenced to a hydrogen maser. The relative separations between the lines are used to evaluate the $^{3}P_{1}$-level magnetic dipole and electric quadrupole constants for the fermionic isotopes. The center of gravity for the $^3P_1$ levels in $^{171}$Yb and $^{173}$Yb are also evaluated, where we find significant disagreement with previously reported values. These hyperfine constants provide a valuable litmus test for atomic many-body computations in ytterbium.

physics.atom-ph↗

arXiv2018

Production of ultracold Cs*Yb molecules by photoassociation

We report the production of ultracold heteronuclear Cs$^*$Yb molecules through one-photon photoassociation applied to an ultracold atomic mixture of Cs and Yb confined in an optical dipole trap. We use trap-loss spectroscopy to detect molecular states below the Cs($^{2}P_{1/2}$) + Yb($^{1}S_{0}$) asymptote. For $^{133}$Cs$^{174}$Yb, we observe 13 rovibrational states with binding energies up to $\sim$500 GHz. For each rovibrational state we observe two resonances associated with the Cs hyperfine structure and show that the hyperfine splitting in the diatomic molecule decreases for more deeply bound states. In addition, we produce ultracold fermionic $^{133}$Cs$^{173}$Yb and bosonic $^{133}$Cs$^{172}$Yb and $^{133}$Cs$^{170}$Yb molecules. From mass scaling, we determine the number of bound states supported by the 2(1/2) excited-state potential to be 154 or 155.

physics.atom-ph↗

arXiv2017

An inverted crossover resonance within one Zeeman manifold

We carry out investigations of inverted crossover resonances in $π$-driven four-level systems where $ΔF$ can be zero. Through the use of sub-Doppler frequency modulation spectroscopy of the $(6s^{2})$ $^{1}S_{0}$ $-$ $(6s6p)$ $^{3}P_{1}$ transition in $^{171}$Yb the resonance becomes manifest. The centre-frequency is inherently insensitive to first-order Zeeman shifts and equates to the two-level resonance frequency in the absence of a magnetic field. A rate equation model is used to help validate the nature of the resonance. Optical frequency measurements of the $F'=1/2$ hyperfine line recorded over two months demonstrate a statistical uncertainty of $2\times10^{-11}$. The inverted crossover resonance found with the $F'=3/2$ line is used for 556 nm laser frequency stabilization, which is an alternative means when applied to magneto-optical trapping of $^{171}$Yb.

physics.atom-ph↗

arXiv2015

Clock and inter-combination line frequency separation in $^{171}$Yb

We have carried out concurrent optical frequency measurements of the $(6s^{2})\,^{1}S_{0} -(6s6p)\,^{3}P_{1}$ ($F=\frac{3}{2}$) and $(6s^{2})\,^{1}S_{0} -(6s6p)\,^{3}P_{0}$ transitions in $^{171}$Yb, and in so doing have determined the frequency separation between the $^{3}P_{0}$ ($F=\frac{1}{2}$) and $^{3}P_{1}$ ($F=\frac{3}{2}$) levels with an uncertainty in the ppb range. The knowledge of this frequency interval will aid experiments relying on the $^{1}S_{0}-\,^{3}P_{0}$ line in $^{171}$Yb and $^{173}$Yb without access to highly accurate frequency standards.

physics.atom-ph↗

arXiv2014

Spectroscopy and laser cooling on the $^{1}S_{0}-\,^{3}P_{1}$ line in Yb via an injection-locked diode laser at 1111.6nm

We generate 555.8nm light with sub-MHz linewidth through the use of laser injection-locking of a semiconductor diode at 1111.6nm, followed by frequency doubling in a resonant cavity. The integrity of the injection lock is investigated by studying an offset-beat signal between slave and master lasers, by performing spectroscopy on the $(6s)^{2}$ $^{1}S_{0}-\,(6s6p)$ $^{3}P_{1}$ transition in magneto-optically trapped ytterbium, and by demonstrating additional laser cooling of $^{171}$Yb with the 555.8nm light. For the $^{1}S_{0}-$ $^{3}P_{1}$ spectroscopy, we confirm the linear dependence between ground state linewidth and the intensity of an off-resonant laser, namely, that used to cool Yb atoms in a $^{1}S_{0}-$ $^{1}P_{1}$ magneto-optical trap. Our results demonstrate the suitability of injection locked 1100-1130nm laser diodes as a source for sub-MHz linewidth radiation in the yellow-green spectrum.

physics.optics↗

arXiv2014

Sub-Doppler cooling of ytterbium with the $^{1}S_{0}$-$^{1}P_{1}$ transition including $^{171}$Yb (I=1/2)

We report on the sub-Doppler laser cooling of neutral $^{171}$Yb and $^{173}$Yb in a magneto-optical trap using the $^{1}S_{0}$-$^{1}P_{1}$ transition at 398.9nm. We use two independent means to estimate the temperature of the atomic cloud for several of the Yb isotopes. The two methods of MOT-cloud-imaging and release-and-recapture show consistency with one another. Temperatures below 400$μ$K and 200$μ$K are recorded for $^{171}$Yb and $^{173}$Yb, respectively, while ~1mK is measured for both $^{172}$Yb and $^{174}$Yb. By comparison, the associated 1D Doppler cooling temperature limit is 694$μ$K. The sub-Doppler cooling of the I=1/2 $^{171}$Yb isotope in a $σ^{+}-σ^{-}$ light-field trap adds further evidence that the Sisyphus cooling mechanism is occurring in such 3D magneto-optical traps.

physics.atom-ph↗