The Standard Model of particle physics is known to be incomplete. Extensions to the Standard Model, such as weak-scale supersymmetry, posit the existence of new particles and interactions that are asymmetric under time reversal (T) and nearly always predict a small yet potentially measurable electron electric dipole moment (EDM), d(e), in the range of 10(-27) to 10(-30) e·cm. The EDM is an asymmetric charge distribution along the electron spin (S(→)) that is also asymmetric under T. Using the polar molecule thorium monoxide, we measured d(e) = (-2.1 ± 3.7stat ± 2.5syst) × 10(-29) e·cm. This corresponds to an upper limit of |d(e)| < 8.7 × 10(-29) e·cm with 90% confidence, an order of magnitude improvement in sensitivity relative to the previous best limit. Our result constrains T-violating physics at the TeV energy scale.

Precision searches for time-reversal symmetry violating interactions in polar molecules are extremely sensitive probes of high energy physics beyond the standard model. To extend the reach of these probes into the PeV regime, long coherence times and large count rates are necessary. Recent advances in laser cooling of polar molecules offer one important tool-optical trapping. However, the types of molecules that have been laser cooled so far do not have the highly desirable combination of features for new physics searches, such as the ability to fully polarize and the existence of internal comagnetometer states. We show that by utilizing the internal degrees of freedom present only in molecules with at least three atoms, these features can be attained simultaneously with molecules that have simple structure and are amenable to laser cooling and trapping. DOI: 10.1103/PhysRevLett.119.133002 Precision measurements of heavy atomic and molecular systems have proven to be a powerful probe of high energy scales in the search for new physics beyond the standard model (BSM) [1]. For example, the limit on the electron's electric dipole moment (EDM), set by the ACME Collaboration using ThO, is sensitive to T-violating BSM physics at the ≳TeV scale [2]. This sensitivity relies on the ability to experimentally access the large effective electromagnetic fields (>10 GV=cm) present in heavy polar molecules by fully polarizing them in the laboratory frame. This makes the experimental challenges of working with such a complex species worth the effort.Despite the success of ACME, a current limitation of that experiment and all present molecular beam experiments is that their coherence time is limited to a few milliseconds by the beam transit time through an apparatus of reasonable size. Since EDM sensitivity scales linearly with coherence time, trapping neutral molecules has the potential to increase sensitivity by many orders of magnitude. 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]. These doublets enable full po...

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.

We propose a new scalable platform for quantum computing (QC)-an array of optically trapped symmetric-top molecules (STMs) of the alkaline earth monomethoxide (MOCH 3 ) family. Individual STMs form qubits, and the system is readily scalable to 100-1000 qubits. STM qubits have desirable features for QC compared to atoms and diatomic molecules. The additional rotational degree of freedom about the symmetric-top axis gives rise to closely spaced opposite parity K-doublets that allow full alignment at low electric fields, and the hyperfine structure naturally provides magnetically insensitive states with switchable electric dipole moments. These features lead to much reduced requirements for electric field control, provide minimal sensitivity to environmental perturbations, and allow for 2-qubit interactions that can be switched on at will. We examine in detail the internal structure of STMs relevant to our proposed platform, taking into account the full effective molecular Hamiltonian including hyperfine interactions, and identify useable STM qubit states. We then examine the effects of the electric dipolar interaction in STMs, which not only guide the design of high-fidelity gates, but also elucidate the nature of dipolar exchange in STMs. Under realistic experimental parameters, we estimate that the proposed QC platform could yield gate errors at the 10 −3 level, approaching that required for fault-tolerant QC.

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Alkaline earth monoalkoxide free radicals (MORs) have molecular properties conducive to direct laser cooling to sub-millikelvin temperatures. Using dispersed laser induced fluorescence measurements from a pulsed supersonic molecular beam source we determine vibrational branching ratios and Franck-Condon factors for the MORs CaOH and CaOCH 3 . With narrow linewidth continuous-wave dye laser excitation, we precisely measure fluorescence branching for both X Ã -˜and X B -˜electronic systems in each molecule. Weak symmetry-forbidden decays to excited bending states with non-zero vibrational angular momentum are observed. Normal mode theoretical analysis combined with ab initio structural calculations are performed and compared to experimental results. Our measurements and analysis pave the way for direct laser cooling of these (and other) complex nonlinear polyatomic molecules. We also describe a possible approach to laser cooling and trapping of molecules with fewer symmetries like chiral species.

Calcium monofluoride (CaF) is magnetically slowed and trapped using optical pumping. Starting from a collisionally cooled slow beam, CaF with an initial velocity of ∼ 30 m/s is slowed via magnetic forces as it enters a 800 mK deep magnetic trap. Employing two-stage optical pumping, CaF is irreversibly loaded into the trap via two scattered photons. We observe a trap lifetime exceeding 500 ms, limited by background collisions. This method paves the way for cooling and magnetic trapping of chemically diverse molecules without closed cycling transitions.