Candidate for Laser Cooling of a Negative Ion: High-Resolution Photoelectron Imaging of Th− (original) (raw)
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Physical Review A, 2021
Despite the fact that the laser cooling method is a well-established technique to obtain ultra-cold neutral atoms and atomic cations, it has so far never been applied to atomic anions due to the lack of suitable electric-dipole transitions. Efforts of more than a decade currently have Laas the only promising candidate for laser cooling. Our previous work [Tang et al., Phys. Rev. Lett. (2019) accept] showed that This also a potential candidate. Here we report on a combination of experimental and theoretical studies to determine the relevant transition frequencies, transition rates, and branching ratios in Th-. The resonant frequency of the laser cooling transition is determined to be /c= 4118.0 (10) cm-1. The transition rate is calculated as A=1.1710 4 s 1. The branching fraction to dark states is very small, 1.47×10-10 , thus this represents an ideal closed cycle for laser cooling. Since Th has zero nuclear spin, it is an excellent candidate to be used to sympathetically cool antiprotons in a Penning trap. The achievement of Bose-Einstein condensation, precision spectroscopy, and tests of fundamental symmetries has opened a new chapter in atomic and molecular physics. The main driving force behind this achievement is the ability to cool atoms and positive ions to K or even lower temperatures via laser cooling techniques. Although laser cooling is a well-established technique for producing ultracold neutral atoms and positive ions, it has not yet been achieved for negative ions. In principle, once we produce ultracold ensembles of a specific anion system, we can use them to sympathetically cool any anions, ranging from elementary particles to molecular anions, which will promote the research of cold plasma[1], ultracold chemistry[2], and fundamental-physics tests[3-8]. In contrast to neutral atoms and positive ions, which have an infinite number of bound states, negative ions have only a single bound state in most cases. The reason is that in atomic anions, the excess
Laser Cooling of Molecular Anions
Physical review letters, 2015
We propose a scheme for laser cooling of negatively charged molecules. We briefly summarize the requirements for such laser cooling and we identify a number of potential candidates. A detailed computation study with C_{2}^{-}, the most studied molecular anion, is carried out. Simulations of 3D laser cooling in a gas phase show that this molecule could be cooled down to below 1 mK in only a few tens of milliseconds, using standard lasers. Sisyphus cooling, where no photodetachment process is present, as well as Doppler laser cooling of trapped C_{2}^{-}, are also simulated. This cooling scheme has an impact on the study of cold molecules, molecular anions, charged particle sources, and antimatter physics.
Laser Cooling of Transition Metal Atoms
We propose the application of laser cooling to a number of transition-metal atoms, allowing numerous bosonic and fermionic atomic gases to be cooled to ultra-low temperatures. The non-zero electron orbital angular momentum of these atoms implies that strongly atom-state-dependent light-atom interactions occur even for light that is far-detuned from atomic transitions. At the same time, many transition-metal atoms have small magnetic dipole moments in their low-energy states, reducing the rate of dipolar-relaxation collisions. Altogether, these features provide compelling opportunities for future ultracold-atom research. Focusing on the case of atomic titanium, we identify the metastable a 5 F5 state as supporting a J → J +1 optical transition with properties similar to the D2 transition of alkali atoms, and suited for laser cooling. The high total angular momentum and electron spin of this state suppresses leakage out of the nearly closed optical transition to a branching ratio estimated below ∼ 10 −5. Following the pattern exemplified by titanium, we identify optical transitions that are suited for laser cooling of elements in the scandium group (Sc, Y, La), the titanium group (Ti, Zr), the vanadium group (V, Nb), the manganese group (Mn, Tc), and the iron group (Fe, Ru). Laser cooling and the achievement of quantum degen-eracy of atomic gases has led to an ever broadening range of scientific investigations and applications. This growing impact on science and technology has been fueled by the availability of quantum gases produced from an increasing number of elements, each of which has a new set of properties that can enable a new family of experiments. For example, the fortuitous collisional properties of ru-bidium and sodium enabled the first realizations of scalar [1, 2] and spinor [3-5] atomic Bose-Einstein condensation. The accessible Feshbach resonances of lithium allowed studies of Efimov states [6]. Isotopes of potassium and lithium allowed the study of resonantly interacting Fermi gases [7-10]. The detectability of single metastable helium atoms on micro-channel plate detectors allowed for studies of quantum atom optics [11]. The narrow lines of alkali-earth atoms and ytterbium enabled the realization of optical lattice clocks [12, 13]. The magnetism of chromium allowed for studies of quantum ferrofluids [14], accentuated by the even stronger magnetic dipole interactions of dysprosium [15] and erbium [16]. Gaining access to a greater variety of ultracold atomic gases can, therefore, be expected to broaden the impact of ultracold atomic physics even further. Conversely, the limitations of present-day ultracold atom systems pose limitations on the range of scientific topics that they can be used to study. As an example, we consider the prospect of studying gases in a stable mixture of internal spin states while subject also to coherent spin-state dependent optical potentials. Each of these two conditions can be achieved separately in extant quantum gases: Stable spinor gases are realized with alkali atoms, whose small magnetic moments forestalls inelastic dipolar relaxation collisions [17]. Highly coherent spin-dependent optical potentials are realized for lanthanide atoms, owing to their complex atomic structures [18]. However, in neither case are both conditions simultaneously achieved: Spin-dependent optical potentials for alkali atoms have low coherence (as we explain in Sec. I). Spinor gases of lanthanide atoms decay generally through strong magnetic dipolar relaxation, although the specific relaxation via collision channels with indistinguishable initial or final spin states can be suppressed by Fermi statistics [19]. Here, we open a door to new studies of quantum atomic gases by describing pathways for laser-cooling a number of transition-metal elements, including those in the scandium group (Sc, Y, La), the titanium group (Ti, Zr, and possibly Hf), the vanadium group (V, Nb), the manganese group (Mn, Tc), and the iron group (Fe, Ru, and possibly Os). Specifically, we find for all these elements that there is a strong, electric-dipole allowed, optical transition (see Tab. I), with linewidth on the order of 10 MHz, which resembles the D2 line of alkali atoms in that an electron is driven from ns 1/2 to the np 3/2 state. The lower level on this transition, which we call the laser-cooling state, is either the atomic ground state (in Ru and Mn) or a metastable excited state (in the other cases). In all cases, these transitions are cycling, or at least very nearly so, and connect states with total angular momentum J → J +1. As such, these transitions are suitable for standard laser cooling techniques such as Zeeman slowing [21], magneto-optical trapping [22], and polarization-gradient cooling [23, 24]. These elements have atomic properties that differ from those of existing ultracold atomic gases. Present-day arXiv:2008.06147v4 [physics.atom-ph] 2 Dec 2020
Challenges of laser-cooling molecular ions
New Journal of Physics, 2011
The direct laser cooling of neutral diatomic molecules in molecular beams suggests that trapped molecular ions can also be laser cooled. The long storage time and spatial localization of trapped molecular ions provides the opportunity for multi-step cooling strategies, but also requires a careful consideration of rare molecular transitions. We briefly summarize the requirements that a diatomic molecule must meet for laser cooling, and we identify a few potential molecular ion candidates. We then perform a detailed computational study of the candidates BH + and AlH + , including improved ab initio calculations of the electronic state potential energy surfaces and transition rates for rare dissociation events. Based on an analysis of population dynamics, we determine which transitions must be addressed for laser cooling and compare experimental schemes using continuous-wave and pulsed lasers.
Journal of The Optical Society of America B-optical Physics, 2003
Trapped and laser-cooled ions are increasingly used for a variety of modern high-precision experiments, for frequency standard applications, and for quantum information processing. Therefore laser cooling of trapped ions is reviewed, the current state of the art is reported, and several new cooling techniques are outlined. The principles of ion trapping and the basic concepts of laser cooling for trapped atoms are introduced. The underlying physical mechanisms are presented, and basic experiments are briefly sketched. Particular attention is paid to recent progress by elucidating several milestone experiments. In addition, a number of special cooling techniques pertaining to trapped ions are reviewed; open questions and future research lines are indicated.
Low-Energy Ions from Laser-Cooled Atoms
Physical Review Applied, 2016
We report the features of an ion source based on two-color photoionization of a laser-cooled cesium beam outsourced from a pyramidal magneto-optical trap. The ion source operates in continuous or pulsed mode. At acceleration voltages below 300 V, it delivers some ten ions per bunch with a relative energy spread ΔU rms =U ≃ 0.032, as measured through the retarding field-energy-analyzer approach. Spacecharge effects are negligible thanks to the low ion density attained in the interaction volume. The performances of the ion beam in a configuration using focused laser beams are extrapolated on the basis of the experimental results. Calculations demonstrate that our low-energy and low-current ion beam can be attractive for the development of emerging technologies requiring the delivery of a small amount of charge, down to the single-ion level and its eventual focusing in the 10-nm range.
Physical Review A, 2004
The translational motion of molecular ions can be effectively cooled sympathetically to translational temperatures below 100 mK in ion traps through Coulomb interactions with laser-cooled atomic ions. The ro-vibrational degrees of freedom, however, are expected to be largely unaffected during translational cooling. We have previously proposed schemes for cooling of the internal degrees of freedom of such translationally cold but internally hot heteronuclear diatomic ions in the simplest case of 1 Σ electronic ground state molecules. Here we present a significant simplification of these schemes and make a generalization to the most frequently encountered electronic ground states of heteronuclear molecular ions: 1 Σ , 2 Σ , 3 Σ and 2 Π . The schemes are relying on one or two laser driven transitions with the possible inclusion of a tailored incoherent far infrared radiation field.
Laser cooling and photoionization of alkali atoms
Applied Surface Science, 2000
We carry out photoionization experiments on laser-cooled alkali atoms by irradiating rubidium and cesium magneto-opti-Ž . cal traps MOTs with a photoionizing laser beam. Analysis of the loading behavior of the traps allows us to determine photoionization cross-sections for the first excited state of rubidium and cesium based on a trap loadrloss model. In addition, our experimental findings reveal systematic peculiarities, which can be ascribed to the low temperature of the atomic samples under investigation. q
High-Resolution Atomic Spectroscopy of Laser-Cooled Ions
2000
The experiments of Dehmelt and his collaborators in the 1960s[l] demonstrated that the stored-ion technique is useful for precise and accurate spectroscopy. The main reasons for this are: 1) Ions can be localized in space for long periods of time. This has the effects that the first-order Doppler shift averages to zero and that, in principle, very high resolution can be obtained because of the long resonance times. 2) When the ions are trapped in high vacuum, the perturbations to their internal structure (caused mainly by second-order Stark shifts [Z]) are small, Historically, trapped-ion temperatures were typically above ambient temperatures so the uncertainty in the second-order Doppler shift limited the accuracy in very-high-resolution experiments. With laser cooling, this uncertainty can be significantly reduced.