Doppler and Sisyphus cooling of 174 YbOH are achieved and studied. This polyatomic molecule has high sensitivity to physics beyond the Standard Model and represents a new class of species for future high-precision probes of new T-violating physics. The transverse temperature of the YbOH beam is reduced by nearly two orders of magnitude to < 600 μK and the phase-space density is increased by a factor of > 6 via Sisyphus cooling. We develop a full numerical model of the laser cooling of YbOH and find excellent agreement with the data. We project that laser cooling and magneto-optical trapping of long-lived samples of YbOH molecules are within reach and these will allow a high sensitivity probe of the electric dipole moment of the electron. The approach demonstrated here is easily generalized to other isotopologues of YbOH that have enhanced sensitivity to other symmetryviolating electromagnetic moments.

Bioaerosols are known to be an important transmission pathway for SARS-CoV-2. We report a framework for estimating the risk of transmitting SARS-CoV-2 via aerosols in laboratory and office settings, based on an exponential dose-response model and analysis of air flow and purification in typical heating, ventilation, and air conditioning (HVAC) systems. High-circulation HVAC systems with high-efficiency particulate air (HEPA) filtration dramatically reduce exposure to the virus in indoor settings, and surgical masks or N95 respirators further reduce exposure. As an example of our risk assessment model, we consider the precautions needed for a typical experimental physical science group to maintain a low risk of transmission over six months of operation. We recommend that, for environments where fewer than five individuals significantly overlap, work spaces should remain vacant for between one (high-circulation HVAC with HEPA filtration) to six (low-circulation HVAC with no filtration) air exchange times before a new worker enters in order to maintain no more than 1% chance of infection over six months of operation in the workplace. Our model is readily applied to similar settings that are not explicitly given here. We also provide a framework for evaluating infection mitigation through ventilation in multiple occupancy spaces.

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We report a generally applicable computational and experimental approach to determine vibronic branching ratios in linear polyatomic molecules to the 10−5 level, including for nominally symmetry-forbidden transitions. These methods are demonstrated in CaOH and YbOH, showing approximately two orders of magnitude improved sensitivity compared with the previous state of the art. Knowledge of branching ratios at this level is needed for the successful deep laser cooling of a broad range of molecular species.

We report the production of ultracold RbCs molecules in the rovibronic ground state, i.e., X 'E +(i; = 0, 7 = 0), by short-range photoassociation to the 23n0 state followed by spontaneous emission. We use narrow-band depletion spectroscopy to probe the distribution of rotational levels formed in the X lL +(u = 0) state. We conclude, based on selection rules, that the primary decay route to X 'E +(i; = 0) is a two-step cascade decay that leads to as much as 33% branching into the 7 = 0 rotational level. The experimental simplicity of our scheme opens up the possibility of easier access to the study and manipulation of ultracold heteronuclear molecules in the rovibronic ground state.Tremendous efforts have been devoted to the produc tion of ultracold samples of heteronuclear molecules over recent years. Promising applications range from quantum computation [1] to ultracold chemistry [2], quantum dipolar physics [3,4], and tests of fundamental physics [3,5]. However, access to dense samples of ground-state ultracold polar molecules has so far been limited to a few outstanding ex periments [6,7], which utilized magnetoassociation followed by transfer to the ground state by stimulated Raman adiabatic passage [8]. A less experimentally complex path toward a sample of ultracold molecules is short-range photoassociation (PA) [9]. Recent discoveries of short-range PA transitions in RbCs [10], NaCs [11], KRb [12], and Rb2 [13,14] proved the general applicability of the process to alkali-metal dimers. Short-range PA is a convenient means to produce ultracold molecules due to its simplicity and possible continuous operation, although PA leads to an unavoidable distribution of molecules over many vibrational, rotational, and hyperfine levels. In fact, to date, short-range PA has predominantly produced molecules in rotationally excited states: ~2% of molecules were observed in J = 0 for LiCs [9] and no 7 = 0 molecules were observed for NaCs [11], However, it has been argued that simple measures may allow removal of excited states following PA [15,16]. Also, it is possible to increase the yield of molecules in the ground state by using vibrational cooling [17] and rotational cooling [18].In this paper, we perform high-resolution depletion spec troscopy [9,19] to measure the distribution of rotational levels in RbCs molecules produced via short-range PA to the 2 3n0 electronic state. We confirm that a large fraction of these X(v = 0) molecules, up to 33%, are in their rovibronic ground states, i.e., X(v = 0,7 = 0). We also show that the formation pathway to X(v = 0) is a two-photon-cascade decay as shown in Fig. 1 (a), as opposed to a direct one-photon decay as was previously supposed [16].Most of our experimental setup has been previously described [16]. 85Rb and Cs atoms are laser cooled and trapped in a dual-species forced dark spontaneous force optical trap (dark SPOT) [21] loaded by alkali-metal dispensers. The overlap of the two atom clouds is optimized 'Present address; PACS number(s): 37.10.M n, 3 3 .1 5 .-e , 3 3 .8 0 ....

Medium resolution (∆ν ∼ 3 GHz) laser-induced fluorescence (LIF) excitation spectra of a rotationally cold sample of YbOH in the 17300-17950 cm -1 range have been recorded using twodimensional (excitation and dispersed fluorescence) spectroscopy. High resolution (∆λ ∼ 0.65 nm) dispersed laser induced fluorescence (DLIF) spectra and radiative decay curves of numerous bands detected in the medium resolution LIF excitation spectra were recorded. The vibronic energy levels of the 2 X + Σ  state were predicted using a discrete variable representation approach and compared with observations. The radiative decay curves were analyzed to produce fluorescence lifetimes.DLIF spectra resulting from high resolution (∆ν < 10 MHz) LIF excitation of individual lowrotational lines in the 2 2 1/ 2 (0,0,0) (0,0,0)bands were also recorded. The DLIF spectra were analyzed to determine branching ratios which were combined with radiative lifetimes to obtain transition dipole moments. The implications for laser cooling and trapping of YbOH are discussed.3

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Rapid and repeated photon cycling has enabled precision metrology and the development of quantum information systems using atoms and simple molecules. Extending optical cycling to structurally complex molecules would provide new capabilities in these areas, as well as in ultracold chemistry. Increased molecular complexity, however, makes realizing closed optical transitions more difficult. Building on already established strong optical cycling of diatomic, linear triatomic, and symmetric top molecules, recent work has pointed the way to cycling of larger molecules, including phenoxides. The paradigm for these systems is an optical cycling center bonded to a molecular ligand. Theory has suggested that cycling may be extended to even larger ligands, like naphthalene, pyrene, and coronene. Herein, we study optical excitation and fluorescent vibrational branching of CaO-, SrO-, and CaO- and find only weak decay to excited vibrational states, indicating a promising path to full quantum control and laser cooling of large arene-based molecules.