Quantum science with ultracold molecules

In this talk, Professor Ospelkaus will report about their recent experiments with quantum gases of polar bosonic 23Na39K molecules. She will first discuss inelastic atom-molecule and molecule-molecule collisions and their origin [1,2,3]. Afterwards she will discuss the control of atom-molecule collisions by Feshbach resonances as well as a proposal for blue shielding of collisions of polar molecules using optical photons at Raman resonance [4].

[1] Kai K. Voges, Philipp Gersema, Mara Meyer zum Alten Borgloh, Torben A. Schulze, Torsten Hartmann, Alessandro Zenesini, and Silke Ospelkaus (2020): Ultracold Gas of Bosonic 23Na39K Ground-State Molecules,  Physical Review Letters 125, 083401 (2020)
[2] Philipp Gersema, Kai K. Voges, Mara Meyer zum Alten Borgloh, Leon Koch, Torsten Hartmann, Alessandro Zenesini, Silke Ospelkaus, Junyu Lin, Junyu He, and Dajun Wang: Probing photoinduced two-body loss of ultracold non-reactive bosonic 23Na87Rb and 23Na39K molecules,  PRL 127, 163401 (2021)
[3] Kai K. Voges, Philipp Gersema, Torsten Hartmann, Silke Ospelkaus, and Alessandro Zenesini (2022): Hyperfine dependent atom-molecule loss analyzed by the analytic solution of few-body loss equations,  Physical Review Research 4, 023184 (2022)
[4] Charbel Karam, Mara Meyer zum Alten Borgloh, Romain Vexiau, Maxence Lepers, Silke Ospelkaus, Nadia Bouloufa-Maafa, Leon Karpa, Olivier Dulieu: Two-photon optical shielding of collisions between ultracold polar molecules, arxiv:2211.08950

In this talk, Dr Guttridge will describe the first observation of Rydberg blockade due to the charge-dipole interaction between an atom and a polar molecule. The experiment involves the creation of a hybrid system consisting of ultracold RbCs molecules and Rb atoms trapped in species-specific optical tweezers. The researchers form weakly bound RbCs molecules by merging together optical tweezers containing Rb and Cs molecules. Strikingly, they find that weakly bound molecules can be produced without the widely used method of magnetoassociation across a Feshbach resonance but instead by exploiting an avoided crossing between atomic and molecular states as a function of tweezer separation. They transfer these weakly bound RbCs molecules to the rovibrational ground state using stimulated Raman adiabatic passage and achieve a one-way efficiency of 91(1)%.  Finally, the researchers observe blockade of the transition to the Rb(52s) Rydberg state due to the charge-dipole interaction with a RbCs molecule in the rovibrational ground state. The blockade they have observed provides a mechanism for conditional and non-destructive state readout of the molecule and opens up many new research directions which Dr Guttridge will briefly discuss.

Understanding and controlling the growth and propagation of quantum correlations and entanglement is an emerging frontier in non-equilibrium many-body physics, and a crucial key step for unlocking the full advantage of quantum systems. In this talk Professor Ana Maria Rey will discuss how in multi-layer spin systems, currently accessible in a broad range of quantum platforms, such as arrays of neutral atoms, Rydberg atoms, magnetic atoms and polar molecules, spin interactions can be utilized to realize in a controllable manner  a variety of correlated pair-production processes. In particular, the author will describe how in bi-layer systems, the capability to select individual layers and prepare targeted initial states, can enable the generation of iconic two-mode squeezing models that feature  exponential growth of entanglement and are relevant in many contexts  ranging  from the foundations of quantum mechanics, to parametric amplification in quantum optics, to the Schwinger effect in high energy physics and Unruh thermal radiation in general relativity. In multi-layers the author will show it is possible to engineer a chiral bosonic Kitaev model featuring chiral propagation of correlations. Overall in this talk Professor Ana Maria Rey will  report how current single layer addressing capabilities can allow shaping  and controlling the temporal growth and spatial propagation of quantum correlations in a variety of spin systems relevant for quantum simulation.  

Stable molecular Fermi gases with strong dipolar interactions provide unique opportunities for studying exotic quantum matter such as p-wave superfluidity and extended Fermi-Hubbard models. Dr Xin-Yu Luo will first show how they prepare a large degenerate Fermi gas of heteronuclear Feshbach molecules [1]. After being transferred to the rovibronic ground state, the scientists stabilize the molecular gas by microwave shielding while inducing strong elastic dipolar collisions. This enables the evaporation of polar molecules to temperatures well below the Fermi temperature [2]. The intermolecular potential can be flexibly tuned by the microwave field, allowing them to observe field-linked resonances in collisions of polar molecules. It provides a universal tuning knob to independently control the dipolar interaction and contact interaction [3]. In the end, Dr Xin-Yu Luo will discuss the perspective of realizing dipolar p-wave superfluidity in polar molecules [4] and their efforts towards further cooling down the molecular gas. 

[1] M. Duda et al, Transition from a polaronic condensate to a degenerate Fermi gas of heteronuclear molecules, Nature Physics 1-6 (2023)
[2] A. Schindewolf et al, Evaporation of microwave-shielded polar molecules to quantum degeneracy, Nature 607, 677 (2022)
[3] X-Y Chen et al, Field-linked resonances of polar molecules, Nature 614, 59 (2023) 
[4] F Deng et al, Effective potential and superfluidity of microwave-dressed polar molecules, arXiv preprint arXiv:2210.13253 (2023)

Polar molecules, due to their intrinsic electric dipole moment and their controllable complexity, are a powerful platform for precision measurement searches for physics beyond the standard model (BSM) and, potentially, for quantum simulation/computation. This has led to many experimental efforts to cool and control molecules at the single quantum state level, including with CaF. Professor Doyle will present work demonstrating entanglement and iSWAP operations with individual CaF molecules in optical tweezers. Polyatomic molecules have attracted new focus as potential novel quantum resources with distinct advantages - and challenges - compared to both atoms and diatomic molecules. He will discuss features of polyatomic molecules that can be used in quantum simulation/computation, the search for BSM physics, and ultracold chemistry. Professor Doyle will discuss the results on the laser cooling of polyatomic molecules into the ultracold regime, including the laser cooling of the polyatomic molecules SrOH, YbOH, CaOH and CaOCH3. Finally, if time permits, he will discuss recent measurements on spin precession in a metastable vibrational bending mode of CaOH, useful for future experiments searching for the electron electric dipole moment, a probe for BSM physics in the >10 TeV range.

Ultracold molecules are a promising platform for precision physics, quantum chemistry, quantum simulation, and quantum information studies. In the last decade, there has been a flurry of interesting activity in the direct laser cooling of molecules, down to temperatures of a few μK. Recently, an optical tweezer array of molecules has been demonstrated. However, owing to the low phase-space density (PSD) of laser cooled polar molecules loaded into conservative traps, collisions in a bulk sample have remained elusive so far, in contrast to ultracold bialkali molecules created via association. Our group is pursuing the goal of reaching quantum degeneracy of YO molecules. 
The PSD in conservative traps is limited largely by inefficient loading (few percent) due to large cloud sizes after sub-doppler cooling of molecules. In this talk, I will present our recent results on the first sub-Doppler magneto-optical trap (MOT) of YO molecules [1]. We observe volume compression by a factor of ~ 300 and temperature reduction by a factor of ~ 60 down to 30 μK in comparison to a conventional red detuned MOT, reaching a PSD several orders of magnitude higher than any previous molecular MOT. Currently, we are working on another cooling mechanism. YO has a low-lying excited state with a narrow transition linewidth of ~7 kHz. Optical photon scattering on this transition will result in cooling the molecules to recoil temperatures of 100s of nK. I will also present our progress so far on the narrow-line cooling of molecules.

[1] Burau et al. arXiv 2212.07472 (2022).