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We report on a comparative analysis of quenched sideband cooling in trapped ions. We introduce a theoretical approach for time-efficient simulation of the temporal cooling characteristics and derive the optimal conditions providing fast laser cooling into the ion’s motional ground state. The simulations were experimentally benchmarked with a single ^172 Yb ^+ ion confined in a linear Paul trap. Sideband cooling was carried out on a narrow quadrupole transition, enhanced with an additional clear-out laser for controlling the effective linewidth of the cooling transition. Quench cooling was thus for the first time studied in the resolved sideband, intermediate and semi-classical regime. We discuss the non-thermal distribution of Fock states during laser cooling and reveal its impact on time dilation shifts in optical atomic clocks.

We develop a method of synthetic frequency generation to construct an atomic clock with blackbody radiation (BBR) shift uncertainties below 10 ^−19 at environmental conditions with a very low level of temperature control. The proposed method can be implemented for atoms and ions, which have two different clock transitions with frequencies ν _1 and ν _2 allowing to form a synthetic reference frequency ν _syn = ( ν _1 − ɛν _2 )/(1 − ɛ ), which is absent in the spectrum of the involved atoms or ions. Calibration coefficient ɛ can be chosen such that the temperature dependence of the BBR shift for the synthetic frequency ν _syn has a local extremum at an arbitrary operating temperature T _0 . This leads to a weak sensitivity of BBR shift with respect to the temperature variations near operating temperature T _0 . As a specific example, the Yb ^+ ion is studied in detail, where the utilized optical clock transitions are of electric quadrupole ( S → D ) and octupole ( S → F ) type. In this case, temperature variations of ±7 K lead to BBR shift uncertainties of less than 10 ^−19 , showing the possibility to construct ultra-precise combined atomic clocks (including portable ones) without the use of cryogenic techniques.

Two approaches for solving the long-standing problem of deep laser cooling of neutral magnesium atoms are proposed. The first one uses optical molasses with orthogonal linear polarizations of light waves. The second approach involves a ‘nonstandard’ magneto-optical trap (NMOT) composed of light waves with elliptical polarizations (in general). Both the widely used semiclassical approach based on the Fokker–Planck equation and quantum treatment fully taking into account the recoil effect are employed for theoretical analysis. The results show the possibility of obtaining temperatures lower than 100 µK simultaneously with a large number of cold atoms ~106 ÷ 107. A new velocity-selective cooling technique allowing one to reach the microkelvin temperature range is also proposed. This technique may have some advantages over, for instance, the shallow-dipole-trap technique utilized by other authors. In the case of magnesium atoms this new technique may be used for obtaining a large number of ultracold atoms (T ~ 1 µK, N  >  105). Such a large number of ultracold atoms is crucial issue for metrological and many other applications of cold atoms. [ABSTRACT FROM AUTHOR]