Triplet-singlet conversion by broadband optical pumping

We demonstrate the conversion of cold Cs_{2} molecules initially distributed over several vibrational levels of the lowest triplet state a^{3}\Sigma_{u}^{+} into the singlet ground state X^{1}\Sigma_{g}^{+}. This conversion is realized by a broadband laser exciting the molecules to a well-chosen state from which they may decay to the singlet state throug\textcolor{black}{h two sequential single-photon emission steps: Th}e first photon populates levels with mixed triplet-singlet character, making possible a second spontaneous emission down to several vibrational levels of the X^{1}\Sigma_{g}^{+} states. By adding an optical scheme for vibrational cooling, a substantial fraction of molecules are transferred to the ground vibrational level of the singlet state. The efficiency of the conversion process, with and without vibrational cooling, is discussed at the end of the article. The presented conversion is general in scope and could be extended to other molecules.Comment: 5 pages, 4 figure

Light-assisted ion-neutral reactive processes in the cold regime: radiative molecule formation vs. charge exchange

We present a combined experimental and theoretical study of cold reactive collisions between laser-cooled Ca+ ions and Rb atoms in an ion-atom hybrid trap. We observe rich chemical dynamics which are interpreted in terms of non-adiabatic and radiative charge exchange as well as radiative molecule formation using high-level electronic structure calculations. We study the role of light-assisted processes and show that the efficiency of the dominant chemical pathways is considerably enhanced in excited reaction channels. Our results illustrate the importance of radiative and non-radiative processes for the cold chemistry occurring in ion-atom hybrid traps.Comment: 5 pages, 4 figure

Ion loss events in a cold Rb-Ca+^+ hybrid trap: photodissociation, black-body radiation and non-radiative charge exchange

We theoretically investigate the collisional dynamics of laser-cooled $^{87}$Rb ground-sate atoms and $^{40}$Ca$^+$ ground-sate ions in the context of the hybrid trap experiment of Ref. [Phys. Rev. Lett. 107, 243202 (2011)], leading to ion losses. Cold $^{87}$Rb$^{40}$Ca$^+$ ground-state molecular ions are created by radiative association, and we demonstrate that they are protected against photodissociation by black-body radiation and by the $^{40}$Ca$^+$ cooling laser at 397~nm. This study yields an interpretation of the direct observation of $^{87}$Rb$^{40}$Ca$^+$ ions in the experiment, in contrast to other hybrid trap experiments using other species. Based on novel molecular data for the spin-orbit interaction, we also confirm that the non-radiative charge-exchange is the dominant loss process for Ca$^+$ and obtain rates in agreement with experimental observations and a previous calculation.Comment: This work is submitted to PRA. More comprehensive version to follow. It includes 15 figures,29 pages, 45 reference

Coherent multidimensional spectroscopy of dilute gas-phase nanosystems

Two-dimensional electronic spectroscopy (2DES) is one of the most powerful spectroscopic techniques, capable of attaining a nearly complete picture of a quantum system including its couplings, quantum coherence properties and its real-time dynamics. While successfully applied to a variety of condensed phase samples, high precision experiments on isolated quantum systems in the gas phase have been so far precluded by insufficient sensitivity. However, such experiments are essential for a precise understanding of fundamental mechanisms and to avoid misinterpretations, e.g. as for the nature of quantum coherences in energy trans-port. Here, we solve this issue by extending 2DES to isolated nanosystems in the gas phase prepared by helium nanodroplet isolation in a molecular beam-type experiment. This approach uniquely provides high flexibility in synthesizing tailored, quantum state-selected model systems of single and many-body properties. For demonstration, we deduce a precise and conclusive picture of the ultrafast coherent dynamics in isolated high-spin Rb2 molecules and present for the first time a dynamics study of the system-bath interaction between a single molecule (here Rb3) and a superfluid helium environment. The results demonstrate the unique capacity to elucidate prototypical interactions and dynamics in tailored quantum systems and bridges the gap to experiments in ultracold quantum science

Polarizability of ultracold Rb2 molecules in the rovibrational ground state of a3Σ+u

We study, both theoretically and experimentally, the dynamical polarizability α(ω) of Rb2 molecules in the rovibrational ground state of a3Σ+u. Taking all relevant excited molecular bound states into account, we compute the complex-valued polarizability α(ω) for wave numbers up to 20000cm−1. Our calculations are compared to experimental results at 1064.5nm (∼9400cm−1) as well as at 830.4nm (∼12000cm−1). Here, we discuss the measurements at 1064.5nm. The ultracold Rb2 molecules are trapped in the lowest Bloch band of a 3D optical lattice. Their polarizability is determined by lattice modulation spectroscopy which measures the potential depth for a given light intensity. Moreover, we investigate the decay of molecules in the optical lattice, where lifetimes of more than 2s are observed. In addition, the dynamical polarizability for the X1Σ+g state is calculated. We provide simple analytical expressions that reproduce the numerical results for α(ω) for all vibrational levels of a3Σ+u as well as X1Σ+g. Precise knowledge of the molecular polarizability is essential for designing experiments with ultracold molecules as lifetimes and lattice depths are key parameters. Specifically the wavelength at ∼1064nm is of interest, since here, ultrastable high power lasers are available

Trap loss in a rubidium crossed dipole trap by short-range photoassociation

Significant two-body losses are observed in an ultracold gas of 85Rb or 87Rb atoms in a crossed dipole trap implemented with a broadband laser with a wavelength around 1071 nm. Using available spectroscopic data on the excited states of Rb2, as well as accurate computed transition dipole moment functions, we interpret these losses as due to photoassociation of deeply bound levels of the 0+u coupled states by the trapping laser, followed by spontaneous emission down to bound levels of the Rb2 ground state thus forming ultracold molecules. The observed ratio of 3.3 between the loss rates of 87Rb and 85Rb is well reproduced by the theoretical model.FAPESPINCT-IQCNP