M. Zawada

Lattice-Induced Frequency Shifts in Sr Optical Lattice Clocks at the 10{sup -17} Level

We present a comprehensive study of the frequency shifts associated with the lattice potential in a Sr lattice clock by comparing two such clocks with a frequency stability reaching 5×10(-17) after a 1 h integration time. We put the first experimental upper bound on the multipolar M1 and E2 interactions, significantly smaller than the recently predicted theoretical upper limit, and give a 30-fold improved upper limit on the effect of hyperpolarizability. Finally, we report on the first observation of the vector and tensor shifts in a Sr lattice clock. Combining these measurements, we show that all known lattice related perturbations will not affect the clock accuracy down to the 10(-17) level, even for lattices as deep as 150 recoil energies.

Polarizabilities of the 87Sr Clock Transition

In this paper, we propose an in-depth review of the vector and tensor polarizabilities of the two energy levels of the 87Sr clock transition whose measurement was reported in [P. G. Westergaard et al., Phys. Rev. Lett. 106, 210801 (2011)]. We conduct a theoretical calculation that reproduces the measured coefficients. In addition, we detail the experimental conditions used for their measurement in two Sr optical lattice clocks, and exhibit the quadratic behaviour of the vector and tensor shifts with the depth of the trapping potential and evaluate their impact on the accuracy of the clock.

Experimental realization of an optical second with strontium lattice clocks

Progress in realizing the SI second had multiple technological impacts and enabled further constraint of theoretical models in fundamental physics. Caesium microwave fountains, realizing best the second according to its current definition with a relative uncertainty of 2-4 × 10(-16), have already been overtaken by atomic clocks referenced to an optical transition, which are both more stable and more accurate. Here we present an important step in the direction of a possible new definition of the second. Our system of five clocks connects with an unprecedented consistency the optical and the microwave worlds. For the first time, two state-of-the-art strontium optical lattice clocks are proven to agree within their accuracy budget, with a total uncertainty of 1.5 × 10(-16). Their comparison with three independent caesium fountains shows a degree of accuracy now only limited by the best realizations of the microwave-defined second, at the level of 3.1 × 10(-16).

Strontium optical lattice clocks for practical realization of the metre and secondary representation of the second

We present a system of two independent strontium optical lattice standards probed with a single shared ultranarrow laser. The absolute frequency of the clocks can be verified by the use of Er:fiber optical frequency comb with the GPS-disciplined Rb frequency standard. We report hertz-level spectroscopy of the clock line and measurements of frequency stability of the two strontium optical lattice clocks.

Cavity mode-width spectroscopy with widely tunable ultra narrow laser

We explore a cavity-enhanced spectroscopic technique based on determination of the absorbtion coefficient from direct measurement of spectral width of the mode of the optical cavity filled with absorbing medium. This technique called here the cavity mode-width spectroscopy (CMWS) is complementary to the cavity ring-down spectroscopy (CRDS). While both these techniques use information on interaction time of the light with the cavity to determine absorption coefficient, the CMWS does not require to measure very fast signals at high absorption conditions. Instead the CMWS method require a very narrow line width laser with precise frequency control. As an example a spectral line shape of P7 Q6 O₂ line from the B-band was measured with use of an ultra narrow laser system based on two phase-locked external cavity diode lasers (ECDL) having tunability of ± 20 GHz at wavelength range of 687 to 693 nm.

Absolute frequency measurement of rubidium 5S–7S two-photon transitions

We report the absolute frequency measurements of rubidium 5S-7S two-photon transitions with an optical frequency comb. The digital lock to the transition, the procedures of evaluating the accuracy budget and measurements of the frequency with the optical frequency comb are tested with a simple setup for the sake of comparison of two optical lattice strontium clocks. The narrow, two-photon transition, 5S-7S (760 nm) is insensitive to a magnetic field and promising candidate for frequency standard. The preformed tests yield the transition frequency with accuracy better than reported previously.

Analysis and calibration of absorptive images of Bose–Einstein condensate at nonzero temperatures

We describe the method allowing quantitative interpretation of absorptive images of mixtures of Bose-Einstein condensate and thermal atoms which reduces possible systematic errors associated with evaluation of the contribution of each fraction and eliminates arbitrariness of most of the previous approaches. By using known temperature dependence of the BEC fraction, the analysis allows precise calibration of the fitting results. The developed method is verified in two different measurements and compares well with theoretical calculations and with measurements performed by another group.

Free-fall expansion of finite-temperature Bose–Einstein condensed gas in the non-Thomas–Fermi regime

We report on our study of the free-fall expansion of a finite-temperature Bose–Einstein condensed cloud of 87Rb. The experiments are performed with a variable total number of atoms while keeping constant the number of atoms in the condensate. The results provide evidence that the Bose–Einstein condensate dynamics depends on the interaction with thermal fraction. In particular, they provide experimental evidence that the thermal cloud compresses the condensate.

Absolute frequency determination of molecular transition in the Doppler regime at kHz level of accuracy

Abstract We measured absolute frequency of the unperturbed P7 P7 O2 B-band transition ν 0 =  434783.5084857(82) GHz and the collisional self-shift coefficient δ = − 9.381 ( 62 ) × 10 − 21  GHz/(molecule/cm3). With Doppler-limited spectroscopy we achieved the relative standard uncertainty of 2 × 10 − 11 on line position, typical for Doppler-free techniques. Shapes of the spectral line were measured with a Pound-Drever-Hall-locked frequency-stabilized cavity ring-down spectrometer referenced to an 88Sr optical atomic clock via an optical frequency comb.

Accuracy budget of the 88Sr optical atomic clocks at KL FAMO

This paper presents a detailed accuracy budget of two independent strontium optical lattice clocks at the National Laboratory FAMO (KL FAMO) probed with a single shared ultra-narrow laser. The combined instability of the two frequency standards was after 105s of averaging.