Cold molecules: Progress in quantum engineering of chemistry and quantum matter

Abstract

Cooling atoms to ultralow temperatures have produced a wealth of opportunities in fundamental physics, precision metrology, and quantum science. The more recent application of sophisticated cooling techniques to molecules, which have been more challenging to develop due to complex molecular structures, has now opened door to the longstanding goal of precisely controlling molecular internal and external degrees of freedom and the resulting interaction processes. This line of research can leverage fundamental insights into how molecules interact and evolve to enable the control of reaction chemistry and the design and realization of a range of advanced quantum materials. 2 Molecules hold a central place in the physical sciences. On the one hand, molecules consisting of a small number of atoms represent the upper limit of complexity we can at present hope to understand in complete detail, starting from quantum mechanics. On the other hand, molecules are the building blocks from which more complex phenomena emerge, including chemistry, condensed matter, and indeed life itself. These molecules then represent a kind of intellectual fulcrum around which we can leverage our complete understanding of small systems to probe and manipulate increasingly complex ones.Precisely controlled studies of molecules started decades ago, with the invention of supersonic molecular beams for cooling (1) and coherent control for manipulation of internal states (2). However, bringing the temperature of molecular gases to the quantum regime is a relatively recent endeavor (3). When molecules move extremely slowly in the laboratory frame, and control of their internal degrees of freedom is achieved at the individual quantum state level, then each step of a complex chemical reaction can in principle be monitored and measured. The energy resolution underpinning such a process would be limited only by fundamental quantum rules that govern the molecular interaction from start to finish. The capability to track in full detail how multiple molecular species approach each other, interact via their evolving potential energy landscape, form intermediates, and re-emerge as final products, all while monitoring the internal and external energy level distributions, may have seemed out of reach only a few years ago.However, thanks to the recent progress in the field of cold molecules, we could soon be able to do precisely that. First-principle understanding of the most fundamental molecular reaction processes will furthermore enable the design and control of complex molecular transformations and materials with powerful functionality. 3Molecules have rich energy level structures, owing to the vibrational and rotational degrees of freedom, compared to atoms. This presents a challenge for cooling technology. However, once we gain control over these molecular degrees of freedom, we create opportunities to take advantage of their unique properties, such as precise manipulation of long-range interactions mediated by molecular electric dipole moments. ...

Determination of CaOH and CaOCH3 vibrational branching ratios for direct laser cooling and trapping

“…Detailed quantum mechanical understanding of dynamics, interactions, and reactions for complex molecules requires precisely targeted preparation of internal molecular states and relative kinetic motions in the gas-phase solvent-free environment [1][2][3]. Supersonic molecular beams have allowed groundbreaking achievements in experimental studies of inelastic and reactive molecular interactions, as well as opened the path to coherent control of internal molecular states [4][5][6][7][8][9].…”

Coherent Bichromatic Force Deflection of Molecules

“…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].…”

Vibrational Quenching of Weakly Bound Cold Molecular Ions Immersed in Their Parent Gas

“…Reactive molecular collisions in the ultracold domain are very appealing from the theoretical point of view [8,9]. Initial preparation of the collision partners with very low kinetic energy and well defined internal states restricts the initially available phase space.…”