We report magnetic confinement of neutral, ground state OH at a density of approximately 3 x 10(3) cm(-3) and temperature of approximately 30 mK. An adjustable electric field sufficiently large to polarize the OH is superimposed on the trap in various geometries, making an overall potential arising from both Zeeman and Stark effects. An effective molecular Hamiltonian is constructed, with Monte Carlo simulations accurately modeling the observed single-molecule dynamics in various trap configurations. Magnetic trapping of cold polar molecules under adjustable electric fields may enable study of low energy dipolar interactions.
We report magnetic confinement of neutral, ground state OH at a density of approximately 3 x 10(3) cm(-3) and temperature of approximately 30 mK. An adjustable electric field sufficiently large to polarize the OH is superimposed on the trap in various geometries, making an overall potential arising from both Zeeman and Stark effects. An effective molecular Hamiltonian is constructed, with Monte Carlo simulations accurately modeling the observed single-molecule dynamics in various trap configurations. Magnetic trapping of cold polar molecules under adjustable electric fields may enable study of low energy dipolar interactions.
The OH molecule is currently of great interest from the perspective of ultracold chemistry, quantum fluids, precision measurement, and quantum computation. Crucial to these applications are the slowing, guiding, confinement, and state control of OH, using electric and magnetic fields. In this article, we show that the corresponding eight-dimensional effective ground-state Stark-Zeeman Hamiltonian is exactly solvable and explicitly identify the underlying chiral symmetry. Our analytical solution opens the way to insightful characterization of the magnetoelectrostatic manipulation of ground-state OH. Based on our results, we also discuss a possible application to the quantum simulation of an imbalanced Ising magnet.
Confining atoms with a combination of optical and magnetic fields has led to the formation of new states of matter and provided a tunable test bed to explore many-body atomic and electronic interactions; however, its extension to molecules has been slow. Ultracold molecules (milikelvin temperatures and below) are of interest for a number of additional applications, including studies of quantum phase transitions and precision spectroscopy. One approach to confining polar molecules has relied on inhomogeneous electric fields. Sawyer et al. present an alternative method that traps molecules magnetically. They demonstrate the technique on hydroxyl (OH) radicals, which have appreciable magnetic as well as electric dipole moments. Lifetimes in the magnetoelectrostatic trap ranged from 20 to 500 ms, depending on the background pressure. The technique allows the additional degree of freedom of an electrical field to be superimposed onto the trapped molecules and should facilitate further studies in the direction of controlled molecular collisions and chemical reactions. — ISO
Research in the field of cold polar molecules is progressing rapidly. An array of interesting\ntopics is being developed including precision measurement and fundamental tests, quantum phase transitions, and ultracold chemistry. In particular, dipolar molecules in well-defined quantum states enable exquisite control of their interactions via applied electric fields. The long-range, anisotropic interaction between dipolar molecules leads to new collision dynamics that could be used for novel collective effects, quantum state engineering, and information processing. The focus of this Thesis is the production of cold samples of neutral OH molecules via Stark deceleration and magnetic trapping for novel collision experiments. This novelty results from our combination of cold external beams and trapped target molecules which facilitates observation of dipolar effects as well as low temperature collision resonances. The large permanent electric dipole moment of OH allows us to precisely tune the lab-frame velocity of the molecular packets from ∼ 500 m/s to rest. We have magnetically trapped OH packets at the terminus of our Stark decelerator at a temperature of 70 mK and density of 106 cm−3. With improved understanding of Stark deceleration, we optimize the decelerator efficiency and its coupling to the magnetic trap. Our latest trap design uses permanent ring magnets to create a three-dimensional magnetic quadrupole field. Use of magnetically trapped OH molecules for collision experiments with external beams allow us the unique opportunity of observing both elastic and inelastic collisions. In addition, the trap confinement yields sensitivity to differential elastic cross sections at low collision energies. This open magnetic trap has allowed measurement of collision cross sections between trapped OH and external supersonic beams of He and D2, the latter of which is of astrophysical interest due to the role of H2-OH collisions in pumping interstellar OH megamasers. The combination of trapped OH molecules and temperature tuned beams of He and D2 has facilitated measurement of the lowest-energy D2-OH collision cross sections yet reported. More recently, we report the first observation of electric-field dependent cross sections between two different species of cold polar molecules - OH and ND3 - thereby demonstrating control over molecular scattering in the cold regime. By combining for the first time the production techniques of Stark deceleration and buffer gas cooling, we increase the molecular interaction time by∼ 105 over traditional crossed-beam experiments to gain enhanced sensitivity at the characteristic densities of cold molecule production.
Cold and ultracold polar molecules with nonzero electronic angular momenta 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 $|f;\phantom{\rule{0.16em}{0ex}}M=+\frac{3}{2}\ensuremath{\rangle}$ parity state to the lower $|e;\phantom{\rule{0.16em}{0ex}}+\frac{3}{2}\ensuremath{\rangle}$ state and observing their trap dynamics under an applied electric bias field. Our observations are very well fit by a simple Landau-Zener model, yielding insight to the rich spectra and dynamics of polar radicals in mixed external fields.
Department of Physics, Willamette University, 900 State Street, Salem, OR 97301, USA(Dated: September 12, 2013)The OH molecule is currently of great interest from the perspective of ultracold chemistry, quan-tum fluids, precision measurement and quantum computation. Crucial to these applications arethe slowing, guiding, confinement and state control of OH, using electric and magnetic fields. Inthis article, we show that the corresponding eight-dimensional effective ground state Stark-ZeemanHamiltonian is exactly solvable and explicitly identify the underlying chiral symmetry. Our analyt-ical solution opens the way to insightful characterization of the magnetoelectrostatic manipulationof ground state OH. Based on our results, we also discuss a possible application to the quantumsimulation of an imbalanced Ising magnet.
Cold, neutral hydroxyl radicals are Stark decelerated and efficiently loaded into a permanent magnetic trap. The OH molecules are trapped in the rovibrational ground state at a density of $\ensuremath{\sim}{10}^{6}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}3}$ and temperature of 70 mK. Collision studies between the trapped OH sample and supersonic beams of atomic He and molecular D2 determine absolute collision cross sections. The He-OH and ${\mathrm{D}}_{2}\mathrm{\text{\ensuremath{-}}}\mathrm{OH}$ center-of-mass collision energies are tuned from $60\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}1}$ to $230\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}1}$ and $145\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}1}$ to $510\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}1}$, respectively, yielding evidence of quantum threshold scattering and resonant energy transfer between colliding particles.