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High-resolution spectroscopy using Stark-decelerated beams. a, Schematic diagram of a microwave spectroscopy experiment at JILA in which a beam of OH radicals is Stark decelerated to 200 m s −1 , and interrogated in a 10-cm-long microwave cavity. PMT: Photomultiplier tube. b, Ramsey microwave spectroscopy for the transition between the F = 2 hyperfine states of the two Λ-doublet components of the rotational ground state of the OH radical. Reprinted with permission from ref. 62. 2006 APS.
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The motion of neutral molecules in a beam can be manipulated with inhomogeneous electric and magnetic fields. Static fields can be used to deflect or focus molecules, whereas time-varying fields can be used to decelerate or accelerate beams of molecules to any desired velocity. We review the possibilities that this molecular-beam technology offers,...
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... violation of time-reversal symmetry 56,57 , in the search for a difference in transition frequency between chiral molecules that are each other's mirror image 58 , and for testing a possible time variation of the proton-to-electron mass ratio 59,60 . Recently, high-resolution microwave spectroscopy was carried out on Stark-decelerated beams of 15 (Fig. 4). In these proof-of-principle experiments, an interaction time of up to a millisecond was obtained. To obtain significantly longer interaction times, a molecular fountain can be used in which molecules are decelerated to a few metres per second, cooled and subsequently launched. The molecules fly upwards before falling back under ...
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... 3,8,[38][39][40][41][42][43] Molecular beams are of significant importance in physical chemistry and molecular physics as they provide a unique opportunity to obtain fundamental insights into molecular photophysics and chemical processes. [44][45][46][47][48] Whereas substantial research was conducted on isolated small molecules and atoms, investigating more complex molecular systems with molecular-level insight is still restricted by many experimental challenges. 14,49,50 One of these challenges is to generate well-defined ensembles of the reactant particles. ...
We report on a new versatile transportable endstation for controlled molecule (eCOMO) experiments providing a combination of molecular beam purification by electrostatic deflection and simultaneous ion and electron detection using velocity-map imaging (VMI). The $b$-type electrostatic deflector provides spatial dispersion of species based on their effective-dipole-moment-to-mass ratio. This enables selective investigation of molecular rotational quantum states, conformers, and molecular clusters. Furthermore, the double-sided VMI spectrometer equipped with two high-temporal-resolution event-driven Timepix3 cameras provides detection of all generated ions independently of their mass-over-charge ratio and electrons. To demonstrate the potential of this novel apparatus, we present experimental results from our investigation of carbonyl sulfide (OCS) after ionization. Specifically, we provide the characterization of the molecular beam, electrostatic deflector, and electron- and ion-VMI spectrometer. The eCOMO endstation delivers a platform for ultrafast dynamics studies using a wide range of light sources from table-top lasers to free-electron-laser and synchrotron-radiation facilities. This makes it suitable for research activities spanning from atomic, molecular, and cluster physics, over energy science and chemistry, to structural biology.
... Seeding the sample, which means mixing it with (usually) a heavier gas, can greatly enhance the cooling capacity of the expansion [32]. Considering that the coefficient γ = c P /c V of the gas is a constant for the observed temperature range (an isentropic, ideal gas expansion), the temperature T of the expanded gas can be calculated as a function of the initial temperature T 0 and of local Mach number: ...
... This development was aimed at acquiring the control of translational, rotational, and internal degrees of freedom of the involved molecular species [1]. The first important achievement concerned the control of velocity and directionality of molecular beams, through the development of the timeof-flight mass-spectrometry [2] and the velocity selection [3], permitting investigation of single-collision processes (see for example [4,5]). ...
Molecular orientation is a fundamental requirement to study and control photoinitiated reactions. Experimental setups that make use of hexapolar electric filters combined with slice-ion imaging detectors were employed in these last years to investigate the photodissociation dynamics of chiral molecules. The final goal is the on-the-fly discrimination of oriented enantiomers, revealed by the different angular distributions in photofragment ion-imaging, as predicted from vector correlation studies. Here, we review experiments of photodissociation of oriented chiral molecules, with the aim of presenting limits emerging from these investigations and perspectives toward the achievement of the ultimate objective.
... Therefore, there are almost no collisions between atoms during travel. Inside and outside the valve, the velocity distribution of the atomic beam and all internal degrees of freedom are identical [66]. In contrast, supersonic ow occurs when λ 0 D o , many collisions take place at the exit of the valve, causing the gas to cool adiabatically during expansion into the vacuum chamber. ...
The development of an experiment to measure the weak value of spin for non-zero mass particles has been outlined. It has been shown how the weak measurement theory allows for a new understanding of quantum mechanical processes through the amplification of small signals and the exploration of phase changes in the wave function. The weak measurement process comprises three stages. In order to measure the weak value of spin, the spin vector of an atomic beam must first be pre-selected into a particular orientation. The atomic beam then travels through two magnets, one with a weak magnetic field gradient imparting a small phase shift, the weak stage, and the other producing a strong magnetic field gradient that splits the spin eigenstates of the system, the strong stage. Both magnets are orientated 90 degrees from one another. This last magnet is referred to as the post-selection stage; this produces a shift (along the weak stage axis) in the probability density from which the weak value can be observed. This thesis describes a full analysis of the weak measurement theory using both the first-order approximation and a case where no approximation is performed. Both scenarios are compared to one another to calculate a unique limit, for which the first-order approximation holds. The experiment utilises a pulsed supersonic beam of spin-1 metastable helium atoms in the 2³S₁ triplet state. A highly collimated atomic beam is produced with an angular divergence of 12 μrad, its spatial half-width can be reduced to 3 μm while maintaining a sufficient signal-to-noise ratio. The spin vector of the atomic beam is set using a hexapole magnet together with a rotatable 50 μm slit attached to its exit. The weak stage is an electromagnet, while the strong stage consists of various grade permanent magnets in order to produce a gradient of ≈50 T/m. Splitting of the spin eigenstates of the system has been observed, along with promising evidence of oscillatory spin transition probabilities. Final results indicate the possibility of obtaining weak measurements for atomic systems, revealing oscillatory changes in the transition amplitude probability density related to the phase changes in the wave function. To the author's knowledge, this is the first-time weak measurements in any form have been applied to atomic systems.
... Neutral particle beams are vital to scientific research and industrial applications [1]. For example, precise manipulation of the kinetic behavior of atoms and molecules can improve the reaction rate of chemical processes [2] and realize the processing of materials at the nanoscale [3]. ...
Accelerating neutral atoms is challenging because such particles are not directly manipulated by electric and magnetic fields as charged particles. In our acceleration scheme, the excited atom requires a sufficiently high gradient acceleration force. The key challenge in laser acceleration experiments is that not only must the photon energy excite atoms to the Rydberg state, but also atoms must not be ionized in an intense laser field. In this Letter, we propose using a chirped laser pulse to achieve the objectives above. The enhancement effect of the pulse chirp on the laser acceleration of neutral particles is investigated via numerical simulation and analytical analysis.
... In order to cool molecules, different techniques have been used, such as direct laser cooling [146,147], buffer gas cooling [148], stark deceleration [149], Sisyphus cooling [150], and evaporative cooling [151]. Only evaporative cooling has so far reached the ultracold regime, however, not for molecules in the total ground state. ...
This thesis aims to develop a deeper theoretical understanding of the collective, dissipative quantum dynamics of cavity-coupled molecular ensembles in three parts: First, a cavity is used in a novel scheme for dissipative formation of ultra-cold ground state molecules with collectively enhanced efficiency, which can be efficiently simulated for very large (> 106 molecules) ensembles. Secondly, the analysis is extended to room-temperature polaritonic chemistry. Here, regimes for modified reaction dynamics are identified for a simple photo-induced electron transfer reaction under incoherent pumping. Then, it is shown that entanglement between vibrational and electro-photonic degrees of freedom can be significantly enhanced by introducing disorder into the system using matrix product state simulations. For the disorder-less regime, further efficient approximations methods are developed. Thirdly, in a recent project, the build-up of operator entanglement is studied in an open spin-chain with dephasing, which is found to exhibit logarithmic growth.
... Some direct methods [48] are based on the production of supersonic beams obtained either by adiabatic expansion or cryogenic processes and do not require any laser. Such beams can then be cooled by means of Stark or Zeeman decelerators [49,50,51,52]. However, these techniques only allow to reach temperatures too far above the desired ultracold regime. ...
For more than 20 years, major advances have been made in the formation, cooling and trapping of dipolar molecules. It is now possible to form molecules in a well-defined quantum state at temperatures on the order of a few hundreds of nanokelvins. The upcoming experimental challenge is to reach for the quantum degeneracy regime to create molecular Bose-Einstein condensates or degenerate Fermi gases, which require higher densities and much lower temperatures. However, these conditions are hard to achieve because many molecules are destroyed or lost in two-body or three-body collisions. The goal of this thesis is to develop shielding methods that can suppress these loss processes. These methods exploit the long-range properties of the dipole-dipole interaction, which can be controlled by applied external fields. Using a time-independent quantum formalism, based on Jacobi or hyperspherical coordinates, I show that a static electric field can be used to reduce the two-body and three-body losses for molecules prepared in their first excited rotational state. I also demonstrate that the two-body losses can be strongly reduced for molecules initially prepared in their ground rotational state using a microwave field. This latter method also provides tools to control the real and imaginary part of the molecule - molecule scattering length, which is a key-parameter that characterizes the stability and the controllabiity of a Bose-Einstein condensate. Finally, I apply the numerical code I have developed to study reactive atom - diatom collisions. This code will also enable studies of three-body recombination and collision-induced dissociation phenomena. All these methods open the door for a rich many-body physics for ultracold molecules, similar to that for ultracold atoms.
... Ultra-cold beams of atom and molecules 1,2 have enabled a wide range of ground-breaking experiments in physics, chemistry and biology, from capturing molecular movies of biologically relevant chemical reactions and bimolecular collisions to testing fundamental aspects of quantum mechanics. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] The free expansion of gas molecules from a room temperature bottle into a high-vacuum chamber through a small pinhole generates molecular beam. This leads to a supersonic expansion of a gas to generate an internally (i.e. ...
... A further requirement is the delivery of dense enough gaseous beams to the interaction region, with typical number densities of 10 10 − 10 12 molecules/cm 3 required. 1,2,10,15 As the research field progressed towards the study of larger, more complex neutral gas-phase molecules, a fundamental physical challenge persists: these large molecules typically exist in the liquid or solid form at room temperature and pressure due to their relative low vapour pressure and high melting point, respectively. Delivering gas-phase jets of large neutral molecules therefore requires a phase transition from a liquid or solid to a gas. ...
Supersonic jets of gas-phase atoms and small molecules have enabled a variety of ultrafast and ultracold chemical studies. However, extension to larger, more complex neutral molecules proves challenging for two reasons: (i) Complex molecules, such as cis-stilbene, exist in a liquid or solid phase at room temperature and ambient pressure and (ii) a unidirectional flow of high-density gaseous beams of such molecules to the interaction region is required. No delivery system currently exists that can deliver dense enough molecular jets of neutral complex molecules without ionizing or exciting the target for use in gas-phase structural dynamics studies. Here, we present a novel delivery system utilizing Tesla valves, which generates more than an order-of-magnitude denser gaseous beam of molecules compared to a bubbler without Tesla valves at the interaction region by ensuring a fast unidirectional flow of the gaseous sample. We present combined experimental and flow simulations of the Tesla valve setup. Our results open new possibilities of studying large complex neutral molecules in the gas-phase with low vapor pressures in future ultrafast and ultracold studies.
... Obviously, our method can also be employed with attractive or tunable interactions [40] and diverging magnetic lenses [41,42]. Interactions are nowadays also exploited to establish non-classical correlations. ...
In contrast to light, matter-wave optics of quantum gases deals with interactions even in free space and for ensembles comprising millions of atoms. We exploit these interactions in a quantum degenerate gas as an adjustable lens for coherent atom optics. By combining an interaction-driven quadrupole-mode excitation of a Bose-Einstein condensate (BEC) with a magnetic lens, we form a time-domain matter-wave lens system. The focus is tuned by the strength of the lensing potential and the oscillatory phase of the quadrupole mode. By placing the focus at infinity, we lower the total internal kinetic energy of a BEC comprising 101(37) thousand atoms in three dimensions to 3/2 kB·38−7+6 pK. Our method paves the way for free-fall experiments lasting ten or more seconds as envisioned for tests of fundamental physics and high-precision BEC interferometry, as well as opens up a new kinetic energy regime.
... Ultra-cold beams of atom and molecules 1,2 have enabled a wide range of ground-breaking experiments in physics, chemistry and biology, from capturing molecular movies of biologically relevant chemical reactions and bimolecular collisions to testing fundamental aspects of quantum mechanics. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] The free expansion of gas molecules from a room temperature bottle into a high-vacuum chamber through a small pinhole generates molecular beam. This leads to a supersonic expansion of a gas to generate an internally (i.e. ...
... A further requirement is the delivery of dense enough gaseous beams to the interaction region, with typical number densities of 10 10 − 10 12 molecules/cm 3 required. 1,2,10,15 As the research field progressed towards the study of larger, more complex neutral gas-phase molecules, a fundamental physical challenge persists: these large molecules typically exist in the liquid or solid form at room temperature and pressure due to their relative low vapour pressure and high melting point, respectively. Delivering gas-phase jets of large neutral molecules therefore requires a phase transition from a liquid or solid to a gas. ...
We report the design and implementation of multiple Tesla type micro valves in the target delivery system of a reaction microscope (ReMi) to study gas phase structural dynamics of complex polyatomic molecules, when no delivery system currently exists that can deliver dense enough molecular jets of neutral complex molecules without ionizing or exciting the target. We show, the Tesla valves provide an efficient unidirectional flow of the cis-stilbene molecules into the ReMi. We demonstrate using a bubbler with Tesla valves an order-of-magnitude increase in the detected stilbene molecular ion signal following the strong-field tunnel ionization (SFTI), compared to conventional bubbler without any Tesla valves. Our results for the first time, opens the door for studying large, complex neutral molecules in the gas-phase with low vapour pressures in future ultrafast studies.
