Microwave state transfer and adiabatic dynamics of magnetically trapped polar molecules

Cold and ultracold polar molecules with nonzero electronic angular momentum are of great interest for studies in quantum chemistry and control, investigations of novel quantum systems, and precision measurement. However, in mixed electric and magnetic fields, these molecules are generically subject to a large set of avoided crossings among their Zeeman sublevels; in magnetic traps, these crossings lead to distorted potentials and trap loss from electric bias fields. We have characterized these crossings in OH by microwave-transferring trapped OH molecules from the upper |f; M = +3/2> parity state to the lower |e; +3/2> state and observing their trap dynamics under an applied electric bias field. Our observations are very well described by a simple Landau-Zener model, yielding insight to the rich spectra and dynamics of polar radicals in mixed external fields.Comment: 5 pages, 4 figures plus supplementary materia

Magneto-electrostatic trapping of ground state OH molecules

We report the magnetic confinement of neutral, ground state hydroxyl radicals (OH) at a density of $\sim3\times10^{3}$ cm$^{-3}$ and temperature of $\sim$30 mK. An adjustable electric field of sufficient magnitude to polarize the OH is superimposed on the trap in either a quadrupole or homogenous field geometry. The OH is confined by an overall potential established via molecular state mixing induced by the combined electric and magnetic fields acting on the molecule's electric dipole and magnetic dipole moments, respectively. An effective molecular Hamiltonian including Stark and Zeeman terms has been constructed to describe single molecule dynamics inside the trap. Monte Carlo simulation using this Hamiltonian accurately models the observed trap dynamics in various trap configurations. Confinement of cold polar molecules in a magnetic trap, leaving large, adjustable electric fields for control, is an important step towards the study of low energy dipole-dipole collisions.Comment: 4 pages, 4 figure

Low-energy molecular collisions in a permanent magnetic trap

Cold, neutral hydroxyl radicals are Stark decelerated and confined within a magnetic trap consisting of two permanent ring magnets. The OH molecules are trapped in the ro-vibrational ground state at a density of $\sim10^{6}$ cm$^{-3}$ and temperature of 70 mK. Collisions between the trapped OH sample and supersonic beams of atomic He and molecular D$_{2}$ are observed and absolute collision cross sections measured. The He--OH and D$_{2}$--OH center-of-mass collision energies are tuned from 60 cm$^{-1}$ to 230 cm$^{-1}$ and 145 cm$^{-1}$ to 510 cm$^{-1}$, respectively, yielding evidence of reduced He--OH inelastic cross sections at energies below 84 cm$^{-1}$, the OH ground rotational level spacing.Comment: 4 pages, 4 figure

Cold heteromolecular dipolar collisions

We present the first experimental observation of cold collisions between two different species of neutral polar molecules, each prepared in a single internal quantum state. Combining for the first time the techniques of Stark deceleration, magnetic trapping, and cryogenic buffer gas cooling allows the enhancement of molecular interaction time by 10$^5$. This has enabled an absolute measurement of the total trap loss cross sections between OH and ND$_3$ at a mean collision energy of 3.6 cm$^{-1}$ (5 K). Due to the dipolar interaction, the total cross section increases upon application of an external polarizing electric field. Cross sections computed from \emph{ab initio} potential energy surfaces are in excellent agreement with the measured value at zero external electric field. The theory presented here represents the first such analysis of collisions between a $^2\Pi$ radical and a closed-shell polyatomic molecule.Comment: 7 pages, 5 figure

Magneto-Optical Trap for Polar Molecules

We propose a method for laser cooling and trapping a substantial class of polar molecules, and in particular titanium (II) oxide (TiO). This method uses pulsed electric fields to nonadiabatically remix the ground-state magnetic sublevels of the molecule, allowing us to build a magneto-optical trap (MOT) based on a quasi-cycling $J'=J"-1$ transition. Monte-Carlo simulations of this electrostatically remixed MOT (ER-MOT) demonstrate the feasibility of cooling TiO to a temperature of 10 $\mathrm{\mu}K$ and trapping it with a radiation-pumping-limited lifetime on the order of 80 ms.Comment: 4 pages, 4 figures, 1 table v2: updated to final published text and figure

Quantum-limited optical time transfer for future geosynchronous links

The combination of optical time transfer and optical clocks opens up the possibility of large-scale free-space networks that connect both ground-based optical clocks and future space-based optical clocks. Such networks promise better tests of general relativity, dark matter searches, and gravitational wave detection. The ability to connect optical clocks to a distant satellite could enable space-based very long baseline interferometry (VLBI), advanced satellite navigation, clock-based geodesy, and thousand-fold improvements in intercontinental time dissemination. Thus far, only optical clocks have pushed towards quantum-limited performance. In contrast, optical time transfer has not operated at the analogous quantum limit set by the number of received photons. Here, we demonstrate time transfer with near quantum-limited acquisition and timing at 10,000 times lower received power than previous approaches. Over 300 km between mountaintops in Hawaii with launched powers as low as 40 $\mu$W, distant timescales are synchronized to 320 attoseconds. This nearly quantum-limited operation is critical for long-distance free-space links where photons are few and amplification costly -- at 4.0 mW transmit power, this approach can support 102 dB link loss, more than sufficient for future time transfer to geosynchronous orbits

Cold heteromolecular dipolar collisions

We present the first experimental observation of cold collisions between two different species of neutral polar molecules, each prepared in a single internal quantum state. Combining for the first time the techniques of Stark deceleration, magnetic trapping, and cryogenic buffer gas cooling allows the enhancement of molecular interaction time by 10$^5$. This has enabled an absolute measurement of the total trap loss cross sections between OH and ND$_3$ at a mean collision energy of 3.6 cm$^{-1}$ (5 K). Due to the dipolar interaction, the total cross section increases upon application of an external polarizing electric field. Cross sections computed from \emph{ab initio} potential energy surfaces are in excellent agreement with the measured value at zero external electric field. The theory presented here represents the first such analysis of collisions between a $^2\Pi$ radical and a closed-shell polyatomic molecule.Comment: 7 pages, 5 figure