Observation of Large Atomic-Recoil Induced Asymmetries in Cold Atom Spectroscopy

The atomic recoil effect leads to large (25 %) asymmetries in simple spectroscopic investigations of Ca atoms that have been laser-cooled to 10 microkelvin. Starting with spectra from the more familiar Doppler-broadened domain, we show how the fundamental asymmetry between absorption and stimulated emission of light manifests itself when shorter spectroscopic pulses lead to the Fourier transform regime. These effects occur on frequency scales much larger than the size of the recoil shift itself, and have not been observed before in saturation spectroscopy. These results are relevant to state-of-the-art optical atomic clocks based on freely expanding neutral atoms.Comment: 4 pages, 3 figure

The optical calcium frequency standards of PTB and NIST

We describe the current status of the Ca optical frequency standards with laser-cooled neutral atoms realized in two different laboratories for the purpose of developing a possible future optical atomic clock. Frequency measurements performed at the Physikalisch-Technische Bundesanstalt (PTB) and the National Institute of Standards and Technology (NIST) make the frequency of the clock transition of 40Ca one of the best known optical frequencies (relative uncertainty 1.2e-14) and the measurements of this frequency in both laboratories agree to well within their respective uncertainties. Prospects for improvement by orders of magnitude in the relative uncertainty of the standard look feasible.Comment: 13 pages, 11 figures, to appear in Comptes Rendus Physiqu

The theory of quantum levitators

We develop a unified theory for clocks and gravimeters using the interferences of multiple atomic waves put in levitation by traveling light pulses. Inspired by optical methods, we exhibit a propagation invariant, which enables to derive analytically the wave function of the sample scattering on the light pulse sequence. A complete characterization of the device sensitivity with respect to frequency or to acceleration measurements is obtained. These results agree with previous numerical simulations and confirm the conjecture of sensitivity improvement through multiple atomic wave interferences. A realistic experimental implementation for such clock architecture is discussed.Comment: 11 pages, 6 Figures. Minor typos corrected. Final versio

Controlling dipole-dipole frequency shifts in a lattice-based optical atomic clock

Motivated by the ideas of using cold alkaline earth atoms trapped in an optical lattice for realization of optical atomic clocks, we investigate theoretically the perturbative effects of atom-atom interactions on a clock transition frequency. These interactions are mediated by the dipole fields associated with the optically excited atoms. We predict resonance-like features in the frequency shifts when constructive interference among atomic dipoles occur. We theoretically demonstrate that by fine-tuning the coherent dipole-dipole couplings in appropriately designed lattice geometries, the undesirable frequency shifts can be greatly suppressed.Comment: 14 pages, 4 figure

Intensity stabilisation of optical pulse sequences for coherent control of laser-driven qubits

We demonstrate a system for intensity stabilisation of optical pulse sequences used in laser-driven quantum control of trapped ions. Intensity instability is minimised by active stabilisation of the power (over a dynamic range of > 104 ) and position of the focused beam at the ion. The fractional Allan deviations in power were found to be < 2.2 × 10−4 for averaging times from 1 to 16,384 s. Over similar times, the absolute Allan deviation of the beam position is < 0.1 μm for a 45 μm beam diameter. Using these residual power and position instabilities, we estimate the associated contributions to infidelity in example qubit logic gates to be below 10−6 per gate

Radio-frequency microplasmas with energies suited to in situ selective cleaning of surface adsorbates in ion microtraps

We have demonstrated a capacitively-coupled, radio-frequency (RF) microplasma inside the 3D electrode structure of an ion microtrap device. For this work, devices with an inter-electrode distance of 340 μm were used. The microplasmas were operated at Ω RF /2π = 23 MHz, in both He and He:N2 gas mixtures, over a range of RF amplitudes (140–220 V) and pressures (250–910 mbar). Spectroscopic analysis of the He I 667 nm and Hα 656 nm emission lines yielded the gas temperature and electron density, which enabled calculation of the mean ion bombardment energy. For the range of operating parameters studied, we calculated mean He+ energies to be between 0.3 and 4.1 eV. While these energies are less than the threshold for He sputtering of hydrocarbon adsorbates on Au, we calculate that the high energy tail of the distribution should remove adsorbate monolayers in as little as 1 min of processing. We also calculate that the distribution is insufficiently energetic to have any significant effect on the Au electrode surface within that duration. Our results suggest that the microplasma technique is suited to in situ selective removal of surface adsorbates from ion microtrap electrodes

Fundamental Physical Constants: Looking from Different Angles

We consider fundamental physical constants which are among a few of the most important pieces of information we have learned about Nature after its intensive centuries-long studies. We discuss their multifunctional role in modern physics including problems related to the art of measurement, natural and practical units, origin of the constants, their possible calculability and variability etc

Doppler cooling and trapping on forbidden transitions

Ultracold atoms at temperatures close to the recoil limit have been achieved by extending Doppler cooling to forbidden transitions. A cloud of ^40Ca atoms has been cooled and trapped to a temperature as low as 6 \mu K by operating a magneto-optical trap on the spin-forbidden intercombination transition. Quenching the long-lived excited state with an additional laser enhanced the scattering rate by a factor of 15, while a high selectivity in velocity was preserved. With this method more than 10% of pre-cooled atoms from a standard magneto-optical trap have been transferred to the ultracold trap. Monte-Carlo simulations of the cooling process are in good agreement with the experiments