Cooling system for a cold atoms sensor and associated cooling method

A method for cooling atoms for an atom-chip cold-atom sensor, said sensor comprising:

• a two-dimensional cooling chamber, being a 2D chamber (Ch2D), kept under ultra-high vacuum and comprising atoms to be cooled, said 2D chamber being placed at least partially inside an integrating cylinder having a Z-axis, said integrating cylinder being configured to illuminate the 2D chamber with a first isotropic light,
• a three-dimensional cooling chamber, being a 3D chamber (Ch3D), kept under ultra-high vacuum and joined to the 2D chamber by an aperture configured to allow said atoms to pass from the 2D chamber to the 3D chamber via movement substantially along the Z-axis, said 3D chamber being placed at least partially inside an integrating sphere configured to illuminate the 3D chamber with a second isotropic light, said atoms to be cooled having a first and a second ground state, said states being hyperfine, the method comprising:
• a cooling first phase implemented during a first period of time (T1) consisting in cooling the atoms and in placing them in one of the two hyperfine ground states (F0), this comprising a step of illuminating the 2D chamber and the 3D chamber with the first and second isotropic light, respectively, said isotropic lights having a cooling frequency (fRefroid) and a repump frequency (fRepomp),
• an optical pumping second phase, implemented after the isotropic lights have been turned off during a second period of time (T2), said second phase being implemented during a third period of time (T3) and being intended to place the atoms in a determined Zeeman sub-level (Z0) of the ground state (F0), said second phase comprising steps, implemented simultaneously in the 3D chamber, of:
• applying a uniform magnetic field,
• illuminating with the second isotropic light having the repump frequency (fRepomp),
• illuminating with a microwave-frequency wave having a plurality of different frequencies, each frequency corresponding to a resonant frequency of a transition between a Zeeman sub-level of the first ground state and a Zeeman sub-level of the second ground state.