Rotational State Microwave Mixing for Laser Cooling of Complex Diatomic Molecules

Abstract

We demonstrate the mixing of rotational states in the ground electronic state using microwave radiation to enhance optical cycling in the molecule yttrium (II) monoxide (YO). This mixing technique is used in conjunction with a frequency modulated and chirped continuous wave laser to slow longitudinally a cryogenic buffer gas beam of YO. We generate a measurable flux of YO below 10 m/s, directly loadable into a three-dimensional magneto-optical trap. This technique opens the door for laser cooling of molecules with more complex structure.

Simulations of the bichromatic force in multilevel systems

“…For any system in which the ground-state multiplicity of degenerate projection quantum states m exceeds the excited-state multiplicity by at least two, there will be two dark states regardless of the polarization of light used to couple the two manifolds [21]. A number of schemes have been developed to prevent or reverse optical pumping of the population into these dark states [8,21], which would otherwise cause the BCF to rapidly diminish to zero. We investigate the two most obvious schemes, one involving the application of a skewed dc magnetic field and the other, rapid switching of the optical polarization state.…”

“…During the past few years, methods for direct laser slowing and cooling of small molecules have progressed remarkably, advancing from a demonstration of modest forces in 2009 all the way to a full realization of magnetooptical trapping at ultracold temperatures [1][2][3][4][5][6][7][8]. Nevertheless, all-optical slowing and cooling is presently applicable only to a small number of molecules, and the present schemes require complex optical configurations with multiple repumping beams to recycle atoms that are lost by unwanted radiative decay into distant "dark" states.…”

A buffer gas beam source for short, intense and slow molecular pulses

“…Molecules in the low velocity tail of such a buffer gas beam can be selected (26,27), trapped (28,29) and cooled (30). Recently, buffer-gascooled beams of a few molecular species have been slowed to low velocity using radiation pressure (31)(32)(33)(34)(35), and CONTACT S. Truppe s.truppe09@imperial.ac.uk The underlying research materials for this article can be accessed at Zenodo (https://doi.org/10.5281/zenodo.995663) and may be used under the Creative Commons CCZero license. these slow molecules have been captured and cooled to low temperatures in magneto-optical traps (36)(37)(38).…”

ShieldingΣ2ultracold dipolar molecular collisions with electric fields

“…Notable among these are alkali dimers with 1 Σ ground states, as well as molecules of 2 Σ symmetry, such as SrF [10,15], RbSr [16], YO [17][18][19], all of current experimental interest. These too may suffer chemical reactions, for example, 2 RbSr → Rb 2 + Sr 2 [20][21][22][23].…”