We demonstrate a simple and nondestructive method for identification of a single molecular ion sympathetically cooled by a single laser cooled atomic ion in a linear Paul trap. The technique is based on a precise nondestructive determination of the molecular ion mass through a measurement of the eigenfrequency of a common motional mode of the two ions. The demonstrated mass resolution is sufficiently high that molecular ion mass doublets can potentially be distinguished from each other. The obtained results represent an important step towards single molecule gas phase chemical physics.

Three-dimensional long-range ordered structures in smaller and near-spherically symmetric Coulomb crystals of 40 Ca + ions confined in a linear rf Paul trap have been observed when the number of ions exceeds ∼1000 ions. This result is unexpected from ground state molecular dynamics (MD) simulations, but found to be in agreement with MD simulations of metastable ion configurations. Previously, three-dimensional long-range ordered structures have only been reported in Penning traps in systems of ∼50,000 ions or more. [3,4,5,6,7,8,9,10,11] and most recently dusty plasmas [12]. In nature, Coulomb crystals are presently expected to exist in exotic dense astrophysical objects [13].Theoretically, it has been found that the thermodynamic properties of infinite OCPs of a single species, are fully characterized by the coupling parameter [14]where Q is the charge of the particles, a ws is the Wigner Seitz radius defined from the zero temperature particle density n 0 by 4πa 3 ws /3 = 1/n 0 . Furthermore, a liquidsolid transition to a body centered cubic (bcc) structure is expected to occur for Γ ∼ 170 [15,16]. For finite OCPs simulations have shown that the situation is more complex, and the properties will depend both on the size and shape of the ion plasma, since surface effects cannot be neglected [17,18,19,20,21].Ion Coulomb crystals, which for more than a decade have been realized with laser-cooled ion plasmas confined by electromagnetic fields in Penning traps [4,5,9] or in radio-frequency (rf) traps [3,6,7,8,10], offer an excellent opportunity to study finite size effects of OCPs under various conditions. The Coulomb crystal structures studied range from one-dimensional (1D) long cylindrical crystals [3,6,7,8] over 2D thin planar crystals [4] to 3D spheroidal crystals [4,5,6,9]. The 3D spheroidal ion Coulomb crystals reported in Refs. [6,7] are composed of concentric ion shells formed under the influence of the surface of the Coulomb crystals. Simulations indicate that the ions form a near-2D hexagonal short-range ordered structure within each shell [18]. Similarly, shell and short-range order have recently been observed in dusty plasma experiments [12].Observations of three-dimensional long-range order in Coulomb crystals have previously only been reported in the case of ∼50,000 or more laser-cooled ions in a Penning trap [4,5,9]. In contrast to Penning traps, in rf traps Coulomb crystals undergo strong quadrupole deformations at the frequency of the applied rf field due to the so-called micro-motion [22] of the ions. Since this motion is known to produce heating [22,23], it has not been obvious that three-dimensional long-range order could be obtained in such traps.In this Letter, we present observations of long-range structure in Coulomb crystals of 40 Ca + ions confined in a linear rf Paul trap. By varying the number of ions in near-spherically symmetric crystals, we have shown that bcc structures indeed can be observed in such traps even with the number of ions being below a thousand.The linear Paul trap used i...

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We report on the loading of large ion Coulomb crystals into a linear Paul trap incorporating a high-finesse optical cavity (F ∼ 3200). We show that, even though the 3-mm diameter dielectric cavity mirrors are placed between the trap electrodes and separated by only 12 mm, it is possible to produce in situ ion Coulomb crystals containing more than 10 5 calcium ions of various isotopes and with lengths of up to several millimeters along the cavity axis. We show that the number of ions inside the cavity mode is in principle high enough to achieve strong collective coupling between the ion Coulomb crystal and the cavity field. The results thus represent an important step towards ion trap based Cavity Quantum ElectroDynamics (CQED) experiments using cold ion Coulomb crystals.

Using the positively charged aniline ion ͑C 6 H 5 NH 2 + ͒ as a test molecule, we demonstrate that it is possible to study consecutive photodissociation of complex molecular ions at the single molecule level in an ion trap. When a single C 6 H 5 NH 2 + ion is exposed to laser light at 397 nm and 294 nm, direct or consecutive photodissociation leads to the production of a range of smaller polyatomic molecular ions such as C 5 H 6 + and C 3 H 3 + . The applied method is very versatile and can, e.g., be used in combination with free electron lasers or synchrotron radiation sources.