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Register a new userA simple imaging solution for chip-scale laser cooling
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We demonstrate a simple stacked scheme that enables absorption imaging through a hole in the surface of a grating magneto-optical trap (GMOT) chip, placed immediately below a micro-fabricated vacuum cell. The imaging scheme is capable of overcoming the reduced optical access and surface scatter that is associated with this chip-scale platform, while further permitting both trapping and imaging of the atoms from a single incident laser beam. The through-hole imaging is used to characterise the impact of the reduced optical overlap volume of the GMOT in the chip-scale cell, with an outlook to an optimised atom number in low volume systems.
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Chip-scale atomic devices built around micro-fabricated alkali vapor cells are at the forefront of compact metrology and atomic sensors. We demonstrate a micro-fabricated vapor cell that is actively-pumped to ultra-high-vacuum (UHV) to achieve laser cooling. A grating magneto optical trap (GMOT) is incorporated with the 4 mm-thick Si/glass vacuum cell to demonstrate the feasibility of a fully-miniaturized laser cooling platform. A two-step optical excitation process in rubidium is used to overcome surface-scatter limitations to the GMOT imaging. The unambiguous miniaturization and form-customizability made available with micro-fabricated UHV cells provide a promising platform for future compact cold-atom sensors.
We propose a sub-Doppler laser cooling mechanism that takes advantage of the unique spectral features and extreme dispersion generated by the phenomenon of electromagnetically induced transparency (EIT). EIT is a destructive quantum interference phenomenon experienced by atoms with multiple internal quantum states when illuminated by laser fields with appropriate frequencies. By detuning the lasers slightly from the dark resonance, we observe that, within the transparency window, atoms can be subject to a strong viscous force, while being only slightly heated by the diffusion caused by spontaneous photon scattering. In contrast to other laser cooling schemes, such as polarization gradient cooling or EIT-sideband cooling, no external magnetic field or strong external confining potential is required. Using a semiclassical approximation, we derive analytically quantitative expressions for the steady-state temperature, which is confirmed by full quantum mechanical numerical simulations. We find that the lowest achievable temperatures approach the single-photon recoil energy. In addition to dissipative forces, the atoms are subject to a stationary conservative potential, leading to the possibility of spatial confinement. We find that under typical experimental parameters this effect is weak and stable trapping is not possible.
We present a scheme for laser cooling applicable for an extremely dilute sample of magnetically trapped antihydrogen atoms($bar{H}$). Exploiting and controlling the dynamical coupling between the $bar{H}$s motional degrees of freedom in a magnetic trap, three-dimensional cooling can be achieved from Doppler cooling on one dimension using the $1s_{1/2}-2p_{3/2}$ transition. The lack of three-dimensional access to the trapped $bar{H}$ and the nearly separable nature of the trapping potential leads to difficulties in cooling. Using realistic models for the spatial variation of the magnetic fields, we find that it should be possible to cool the $bar{H}$s to $sim 20$ mK even with these constraints.
The NL-eEDM collaboration is building an experimental setup to search for the permanent electric dipole moment of the electron in a slow beam of cold barium fluoride molecules [Eur. Phys. J. D, 72, 197 (2018)]. Knowledge of molecular properties of BaF is thus needed to plan the measurements and in particular to determine an optimal laser-cooling scheme. Accurate and reliable theoretical predictions of these properties require incorporation of both high-order correlation and relativistic effects in the calculations. In this work theoretical investigations of the ground and the lowest excited states of BaF and its lighter homologues, CaF and SrF, are carried out in the framework of the relativistic Fock-space coupled cluster (FSCC) and multireference configuration interaction (MRCI) methods. Using the calculated molecular properties, we determine the Franck-Condon factors (FCFs) for the $A^2Pi_{1/2} rightarrow X^2Sigma^{+}_{1/2}$ transition, which was successfully used for cooling CaF and SrF and is now considered for BaF. For all three species, the FCFs are found to be highly diagonal. Calculations are also performed for the $B^2Sigma^{+}_{1/2} rightarrow X^2Sigma^{+}_{1/2}$ transition recently exploited for laser-cooling of CaF; it is shown that this transition is not suitable for laser-cooling of BaF, due to the non-diagonal nature of the FCFs in this system. Special attention is given to the properties of the $A^2Delta$ state, which in the case of BaF causes a leak channel, in contrast to CaF and SrF species where this state is energetically above the excited states used in laser-cooling. We also present the dipole moments of the ground and the excited states of the three molecules and the transition dipole moments (TDMs) between the different states.
We demonstrate a compact laser source suitable for the trapping and cooling of potassium. By frequency doubling a fiber laser diode at 1534 nm in a waveguide, we produce 767 nm laser light. A current modulation of the diode allows to generate the two required frequencies for cooling in a simple and robust apparatus. We successfully used this laser source to trap ^39 K.
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