Radio Frequency Magneto-Optical Trapping of CaF with High Density

Abstract

We demonstrate significantly improved magneto-optical trapping of molecules using a very slow cryogenic beam source and either rf modulated or dc magnetic fields. The rf magneto-optical trap (MOT) confines 1.0ð3Þ × 105 CaF molecules at a density of 7ð3Þ × 10 6 cm −3 , which is an order of magnitude greater than previous molecular MOTs. Near Doppler-limited temperatures of 340ð20Þ μK are attained. The achieved density enables future work to directly load optical tweezers and create optical arrays for quantum simulation. DOI: 10.1103/PhysRevLett.119.103201 The field of ultracold molecules is rapidly expanding, pushed forward by favorable prospects for advances in quantum simulation [1,2], quantum information [3,4], quantum chemistry [5,6], and precision measurements [7,8]. The rich internal structure of molecules, including rotational and vibrational modes, as well as their long-range and anisotropic dipolar interactions, make diatomic molecules ideal extensions of current work in these fields. While great progress has been made by assembling bi-alkalis [9-11], direct cooling of molecules allows one to realize an increase in chemical diversity. This diversity is of particular interest in the case of 2 Σ molecules, where the unpaired electron spin would allow one to realize lattice spin models [1,12] and the onset of topologically ordered states [13].The same internal degrees of freedom that make molecules so interesting for scientific applications add further complexity to the cooling and trapping process. Despite this, several groups have sought to cool molecules using direct laser cooling with simultaneous application of multiple laser frequencies, in particular, the construction of molecular MOTs. Magneto-optical traps (MOTs) have long been the workhorse of cold atom experiments, producing (sub-)Doppler-limited temperatures of many atomic species. Recently, following the first demonstration of 2D magneto-optical compression of YO [14], the first dc and rf molecular MOTs were created with SrF [15][16][17]. A major challenge in reaching this point was the very low capture velocity of the molecular MOT due to many internal molecular states and the resulting low photon scattering rate. To extend the MOT to other species and improve the number of trapped molecules, laser slowing of YO [18] and CaF [19,20], rf magneto-optical compression of CaF [21], and, very recently, a MOT of CaF based on static magnetic fields (dc MOT) were demonstrated [22].

Precision Measurement of Time-Reversal Symmetry Violation with Laser-Cooled Polyatomic Molecules

“…As an example of what sort of gains are to be had with this approach, consider 10 6 trapped molecules [11] with 10 second coherence time [43,44], 50% combined preparation and detection efficiency, and one week of operation. Such an experiment would increase sensitivity to the electron EDM by 4 orders of magnitude above the current limit, reaching into the PeV regime [2,45].…”

“…Trapped molecular ions have shown great power in EDM searches [3], primarily due to their long coherence time of ∼1 s. Neutral species offer the ability to increase the number of trapped molecules much more easily and essentially without limit compared to ions, while retaining strong robustness against systematic errors. Here we show that laser-cooled and trapped polyatomic molecules offer a combination of features not available in other systems, including long lifetimes, robustness against systematic errors, and scalability, and present a feasible approach to access PeV-scale BSM physics.A very promising route to trapping EDM-sensitive molecules is direct laser cooling and trapping from cryogenic buffer gas beams (CBGBs), which has advanced tremendously in the last few years [4][5][6][7][8][9][10][11]. The molecules that have been cooled so far posses an electronic structure that makes them amenable to laser cooling, but also precludes the existence of Ω doublets, such as the 3 Δ 1 molecular state used in the two most sensitive electron EDM measurements [2,3].…”

“…A very promising route to trapping EDM-sensitive molecules is direct laser cooling and trapping from cryogenic buffer gas beams (CBGBs), which has advanced tremendously in the last few years [4][5][6][7][8][9][10][11]. The molecules that have been cooled so far posses an electronic structure that makes them amenable to laser cooling, but also precludes the existence of Ω doublets, such as the 3 Δ 1 molecular state used in the two most sensitive electron EDM measurements [2,3].…”

Laser-coolable polyatomic molecules with heavy nuclei

“…Recently highly-efficient cooling and magneto-optical trapping of diatomic molecules was demonstrated for SrF [2], YO [3] and CaF [4,5]. The experiments on Doppler/Sisyphus cooling on BaH [6], MgF [7] and some other molecules and their cations are currently conducted by different groups.…”

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

“…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). The high intensity and low velocity of the beams produced by the buffer gas method was crucial to the success of these experiments.…”