We perform magnetically-assisted Sisyphus laser cooling of the triatomic free radical strontium monohydroxide (SrOH). This is achieved with principal optical cycling in the rotationally closed P (N = 1) branch of either theX 2 Σ + (000) ↔Ã 2 Π 1/2 (000) or theX 2 Σ + (000) ↔B 2 Σ + (000) vibronic transitions. Molecules lost into the excited vibrational states during the cooling process are repumped back through theB (000) state for both the (100) level of the Sr-O stretching mode and the 02 0 0 level of the bending mode. The transverse temperature of a SrOH molecular beam is reduced in one dimension by two orders of magnitude to ∼ 700 µK. This approach opens a path towards creating a variety of ultracold polyatomic molecules, including much larger ones, by means of direct laser cooling.Compared to atoms, the additional rotational and vibrational degrees of freedom in molecules give rise to a wide variety of potential and realized scientific applications, including quantum computation [1][2][3], precision measurements [4][5][6][7], and quantum simulation [8,9]. While ultracold diatomic molecules will be extremely valuable in opening novel research frontiers, molecules with three or more atoms have unique capabilities enabled by their significantly more complicated structure [10][11][12][13][14][15][16]. For all molecules to achieve their full scientific potential, they must be cooled. Yet, the desired quantum complexity that molecules provide also leads to challenges for control, detection, and cooling [17]. Assembling ultracold molecules from two laser-cooled atoms has represented one solution and has created ultracold bi-alkali molecules [18][19][20][21][22], including filling of optical lattices with KRb [23]. There are several direct cooling techniques that together routinely cool a much wider variety of molecules into the Kelvin regime [17,24]. Intense research is ongoing to bring these cold molecules into the ultracold regime (< 1 mK). Even though there has been experimental progress on control of polyatomics [25][26][27][28][29][30], optoelectrical cooling of formaldehyde is the only technique that has resulted in a trapped sub-millikelvin sample [31].Cooling of the external motion of neutral atoms from above room temperature into the sub-millikelvin range (leading to, e.g., Bose-Einstein condensation) commonly relies on the use of velocity-dependent optical forces [32]. Laser cooling requires reasonably closed and strong optical electronic transitions, so its use for molecules has been severely limited. Recently, following initial theoretical proposals [33,34] In this Letter, we report the Sisyphus laser cooling of a polyatomic molecule. The dissipative force for compressing phase-space volume is achieved by a combination of spatially varying light shifts and optical pumping into dark sub-levels, which are then remixed by a static magnetic field, as explored previously in atomic systems [45,46]. Since the magnitude of the induced friction force is directly related to the modulation depth of the dressed e...

An experimentally feasible strategy for direct laser cooling of polyatomic molecules with six or more atoms is presented. Our approach relies on the attachment of a metal atom to a complex molecule, where it acts as an active photon cycling site. We describe a laser cooling scheme for alkaline earth monoalkoxide free radicals taking advantage of the phase space compression of a cryogenic buffer-gas beam. Possible applications are presented including laser cooling of chiral molecules and slowing of molecular beams using coherent photon processes.

Ultracold polyatomic molecules have potentially wide-ranging applications in quantum simulation and computation, particle physics, and quantum chemistry. For atoms and small molecules, direct laser cooling has proven to be a powerful tool for quantum science in the ultracold regime. However, the feasibility of laser-cooling larger, nonlinear polyatomic molecules has remained unknown because of their complex structure. We laser-cooled the symmetric top molecule calcium monomethoxide (CaOCH3), reducing the temperature of ~104 molecules from 22 ± 1 millikelvin to 1.8 ± 0.7 millikelvin in one dimension and state-selectively cooling two nuclear spin isomers. These results demonstrate that the use of proper ro-vibronic transitions enables laser cooling of nonlinear molecules, thereby opening a path to efficient cooling of chiral molecules and, eventually, optical tweezer arrays of complex polyatomic species.

We demonstrate a 1D magneto-optical trap of the polar free radical calcium monohydroxide (CaOH). A quasi-closed cycling transition is established to scatter ∼ 10 3 photons per molecule, predominantly limited by interaction time. This enables radiative laser cooling of CaOH while compressing the molecular beam, leading to a significant increase in on-axis beam brightness and reduction in temperature from 8.4 mK to 1.4 mK.

Vibrational relaxation of strontium monohydroxide (SrOH) molecules in collisions with helium (He) at 2 K is studied. We find the diffusion cross section of SrOH at 2.2 K to be σ = ± × − (5 2) 10 cm d 14

We demonstrate multiple photon cycling and radiative force deflection on the triatomic free radical strontium monohydroxide (SrOH). Optical cycling is achieved on SrOH in a cryogenic buffer-gas beam by employing the rotationally closed P (N = 1) branch of the vibronic transitionX 2 Σ + (000) ↔Ã 2 Π 1/2 (000). A single repumping laser excites the Sr-O stretching vibrational mode, and photon cycling of the molecule deflects the SrOH beam by an angle of 0.2 • via scattering of ∼ 100 photons per molecule. This approach can be used for direct laser cooling of SrOH and more complex, isoelectronic species.

We demonstrate the coherent optical bichromatic force on a molecule, the polar free radical strontium monohydroxide (SrOH). A dual-frequency retro-reflected laser beam addressing theX 2 Σ + ↔Ã 2 Π 1/2 electronic transition coherently imparts momentum onto a cryogenic beam of SrOH. This directional photon exchange creates a bichromatic force that transversely deflects the molecules. By adjusting the relative phase between the forward and counter propagating laser beams we reverse the direction of the applied force. A momentum transfer of 70 k is achieved with minimal loss of molecules to dark states. Modeling of the bichromatic force is performed via direct numerical solution of the time-dependent density matrix and is compared with experimental observations. Our results open the door to further coherent manipulation of molecular motion, including the efficient optical deceleration of diatomic and polyatomic molecules with complex level structures.Laser manipulation of atomic motion has revolutionized atomic, molecular and optical (AMO) physics [1,2]. The widely-used techniques of laser cooling and trapping made possible the creation of ultracold degenerate quantum gases [3], simulation of important condensed matter models [4] and development of new quantum sensors [5,6] and clocks [7]. Laser deceleration and cooling of atomic beams -a necessary part of the trap loading process -typically requires scattering tens of thousands of photons in order to bring room (or oven) temperature atoms to velocities where they can be confined by electromagnetic traps for further studies [8]. While beam deceleration employing the spontaneous radiation pressure force has been a standard for atomic experiments, its application to slowing molecular beams has been limited by the small change in kinetic energy per scattered photon and the myriad of internal molecular states, which inhibits photon cycling. At the same time, there is extreme interest in creating ultracold molecules for new physics applications [9].Neutral diatomic molecules are predicted to play an important role in diverse research areas of modern physics such as quantum simulation [10] and computation [11], as well as searches for new particles and fields beyond the Standard Model [12]. Larger polyatomic molecules will provide additional opportunities in physics and chemistry [13][14][15]. For example, exploring the origin of biomolecular homochirality [16] and understanding primordial chemistry leading to the development of organic life requires the use of large molecules [17]. However, these molecules' complexity presents significant challenges for direct laser slowing and cooling. Yet these are the key ingredients that allow for optical trapping, which, in turn, realizes long moleculelaser coherence times and high levels of quantum state control. Previously, the external motion of gas-phase polyatomic molecules has been manipulated with off-resonant laser fields [18] as well as electric [19], magnetic [20], and mechanical techniques [21]. Inspired by the success of...

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