Quantum technologies with cold molecular ions and polar molecules

Jordi Mur-Petit

Jordi Mur-Petit

Experimental advances in the production of cold molecules in the last years have triggered a flurry of theoretical work in fields as diverse as precision spectroscopy, controlled chemistry, fundamental physics, or quantum computation and simulation [1,2]. Progress on these lines naturally demands an increasing level of precision in the measurement and control of molecular states and properties. In this talk, I will present two of our recent contributions to this end. First, I will review some ideas and tools of cold atomic physics and quantum information that underlie our work. Then, I will introduce a quantum spectroscopy protocol for molecular ions based on their interaction with trapped atomic ions and phase gates [3]. After this, I will show how these ideas can be generalized to enable the measurement of a polar molecule's electric dipole moment [4]. Finally, I will discuss some of our ongoing work to use cold polar molecules for quantum simulation and quantum metrology.

T Suganuma, K. Okada, Naoki Kimura +3 more

A Stark velocity filter has been developed for studying molecular ion-polar molecule reactions at very low temperatures. We have successfully produced slow polar molecules of ND 3 , NH 3 and CH 2 O with a peak velocity of lower than 40 m/s. The property of the Stark velocity filter was systematically studied by changing the Stark voltage, the nozzle pressure and the source gas temperature. Finally the number density of the extracted slow molecules was determined.

Ana María Rey

K. Okada, T Suganuma, Takahiro Furukawa +3 more

We have developed a combined Stark-velocity-filter--ion-trap apparatus for the purpose of reaction-rate measurements between cold trapped ions and slow polar molecules under ultrahigh vacuum conditions. The prerequisite steps such as the characterization of velocity-selected polar molecules (PM), namely ND${}_{3}$, H${}_{2}$CO, and CH${}_{3}$CN, were performed using time-of-flight (TOF) measurements. We confirmed the generation of slow ND${}_{3}$, H${}_{2}$CO, and CH${}_{3}$CN molecules having thermal energies of a few Kelvin. Additionally, the number densities of the slow velocity-filtered polar molecules were determined to be in the range of $n={10}^{4}$ to 10${}^{6}$ cm${}^{\ensuremath{-}3}$ by calibrating the TOF signals. In a first experiment, the Stark velocity filter was connected to a cryogenic linear Paul trap and reaction-rate measurements between laser-cooled Ca${}^{+}$ Coulomb crystals and velocity-selected polar molecules were carried out. The observed reaction rates are of the order of 10${}^{\ensuremath{-}5}$ s${}^{\ensuremath{-}1}$, which are much slower than typical reaction rates of molecular ion--polar-molecule reactions at low temperatures. The present results confirm that reaction-rate measurements between velocity-selected polar molecules and sympathetically cooled molecular ions cooled by a laser-cooled Ca${}^{+}$ Coulomb crystal can be performed. Next we measured the reaction rates between sympathetically cooled nonfluorescent stored ion molecules namely N${}_{2}$H${}^{+}$ ions and velocity-selected CH${}_{3}$CN molecules at the average reaction energy of about 3 K. The measured reaction rate of 2.0(2)$\ifmmode\times\else\texttimes\fi{}$10${}^{\ensuremath{-}3}$ s${}^{\ensuremath{-}1}$ is much faster than those of the Ca${}^{+}$+PM reactions. This is strong evidence that the velocity-selected polar molecules undergo reactive collisions. We also confirmed that the present reaction-rate constant of CH${}_{3}$CN+N${}_{2}$H${}^{+}$ $\ensuremath{\rightarrow}$ CH${}_{3}$CNH${}^{+}$+N${}_{2}$ is consistent with the estimated values from the room temperature results and the trajectory-scaling formula of Su et al. In the future, the present velocity-filter combined cryogenic trap apparatus will enable us to perform systematic measurements of cold ion--polar-molecule reactions, which are important problems from a fundamental viewpoint and also contribute to astrochemistry.

John M. Doyle