Manipulating cold atoms in an ultrahigh vacuum is central to numerous sorts of fundamental and applied physics experiments, including quantum sensing, atom interferometry, optical one-way barriers, particle flux detection, collisional dynamics of atoms, and others. Often, cold atoms are obtained by heating a solid piece of some element in vacuum to increase the partial pressure around the sample so that it emits atoms, collecting the atoms in a trap such as a magneto-optical trap and cooling them, and then transferring the atoms from the preparation chamber to a separate science chamber. The transfer methods consist of different lossy magnetic or magneto-optical techniques; the loss can be reduced by using a magnetic waveguide, but this only works for atoms that are paramagnetic in their ground state.
Now, scientists at the University of São Paulo (São Carlos, Brazil) have come up with a nonmagnetic technique to channel cold atoms from one vacuum chamber to another: a hollow Bessel light beam into which cold atoms are injected. The beam, which can be created using optics consisting of one axicon lens and one conventional focusing lens, acts as a cylindrical light trap that conveys atoms along the resulting light tube. Computer simulations of a Bessel beam produced by an axicon from a Gaussian laser beam with a 0.5 mm diameter, a 461 nm wavelength, and a power of 10 mW show the ability to channel cold atoms over lengths of a couple hundred millimeters. A hollow Bessel beam profile was measured experimentally and corresponds well with the simulation. For strontium atoms precooled to 10 mK, simulated loading efficiency was 20%, but could be increased to 80% by increasing Bessel beam power and tuning the laser wavelength precisely. Reference: D. Rivero et al., arXiv:2010.09792v1 [physics atom-ph] (Oct. 19, 2020).
