arXiv subjects

B. Neyenhuis

Publications and source records attributed to B. Neyenhuis.

24 records · Page 2Linked to original sources

arXiv2009

Quantum-State Controlled Chemical Reactions of Ultracold KRb Molecules

How does a chemical reaction proceed at ultralow temperatures? Can simple quantum mechanical rules such as quantum statistics, single scattering partial waves, and quantum threshold laws provide a clear understanding for the molecular reactivity under a vanishing collision energy? Starting with an optically trapped near quantum degenerate gas of polar $^{40}$K$^{87}$Rb molecules prepared in their absolute ground state, we report experimental evidence for exothermic atom-exchange chemical reactions. When these fermionic molecules are prepared in a single quantum state at a temperature of a few hundreds of nanoKelvins, we observe p-wave-dominated quantum threshold collisions arising from tunneling through an angular momentum barrier followed by a near-unity probability short-range chemical reaction. When these molecules are prepared in two different internal states or when molecules and atoms are brought together, the reaction rates are enhanced by a factor of 10 to 100 due to s-wave scattering, which does not have a centrifugal barrier. The measured rates agree with predicted universal loss rates related to the two-body van der Waals length.

physics.atom-ph↗

arXiv2009

Controlling the hyperfine state of rovibronic ground-state polar molecules

Ultracold molecules offer entirely new possibilities for the control of quantum processes due to their rich internal structure. Recently, near quantum degenerate gases of molecules have been prepared in their rovibronic ground state. For future experiments, it is crucial to also control their hyperfine state. Here, we report the preparation of a rovibronic ground state molecular quantum gas in a single hyperfine state and in particular in the absolute lowest quantum state. The demonstrated and presented scheme is general for bialkali polar molecules and allows the preparation of molecules in a single hyperfine state or in an arbitrary coherent superposition of hyperfine states. The scheme relies on electric-dipole, two-photon microwave transitions through rotationally excited states and makes use of electric nuclear quadrupole interactions to transfer molecular population between different hyperfine states.

physics.atom-ph↗

arXiv2008

Ultracold polar molecules near quantum degeneracy

We report the creation and characterization of a near quantum-degenerate gas of polar $^{40}$K-$^{87}$Rb molecules in their absolute rovibrational ground state. Starting from weakly bound heteronuclear KRb Feshbach molecules, we implement precise control of the molecular electronic, vibrational, and rotational degrees of freedom with phase-coherent laser fields. In particular, we coherently transfer these weakly bound molecules across a 125 THz frequency gap in a single step into the absolute rovibrational ground state of the electronic ground potential. Phase coherence between lasers involved in the transfer process is ensured by referencing the lasers to two single components of a phase-stabilized optical frequency comb. Using these methods, we prepare a dense gas of $4\cdot10^4$ polar molecules at a temperature below 400 nK. This fermionic molecular ensemble is close to quantum degeneracy and can be characterized by a degeneracy parameter of $T/T_F=3$. We have measured the molecular polarizability in an optical dipole trap where the trap lifetime gives clues to interesting ultracold chemical processes. Given the large measured dipole moment of the KRb molecules of 0.5 Debye, the study of quantum degenerate molecular gases interacting via strong dipolar interactions is now within experimental reach.

physics.atom-ph↗

arXiv2008

A High Phase-Space-Density Gas of Polar Molecules

A quantum gas of ultracold polar molecules, with long-range and anisotropic interactions, would not only enable explorations of a large class of many-body physics phenomena, but could also be used for quantum information processing. We report on the creation of an ultracold dense gas of 40K87Rb polar molecules. Using a single step of STIRAP (STImulated Raman Adiabatic Passage) via two-frequency laser irradiation, we coherently transfer extremely weakly bound KRb molecules to the rovibrational ground state of either the triplet or the singlet electronic ground molecular potential. The polar molecular gas has a peak density of 10^12 cm^-3, and an expansion-determined translational temperature of 350 nK. The polar molecules have a permanent electric dipole moment, which we measure via Stark spectroscopy to be 0.052(2) Debye for the triplet rovibrational ground state and 0.566(17) Debye for the singlet rovibrational ground state. (1 Debye= 3.336*10^-30 C m)

quant-ph↗

arXiv2008

Ultracold dense gas of deeply bound heteronuclear molecules

Recently, the quest for an ultracold and dense ensemble of polar molecules has attracted strong interest. Polar molecules have bright prospects for novel quantum gases with long-range and anisotropic interactions, for quantum information science, and for precision measurements. However, high-density clouds of ultracold polar molecules have so far not been produced. Here, we report a key step towards this goal. Starting from an ultracold dense gas of heteronuclear 40K-87Rb Feshbach molecules with typical binding energies of a few hundred kHz and a negligible dipole moment, we coherently transfer these molecules into a vibrational level of the ground-state molecular potential bound by >10 GHz. We thereby increase the binding energy and the expected dipole moment of the 40K-87Rb molecules by more than four orders of magnitude in a single transfer step. Starting with a single initial state prepared with Feshbach association, we achieve a transfer efficiency of 84%. While dipolar effects are not yet observable, the presented technique can be extended to access much more deeply bound vibrational levels and ultimately those exhibiting a significant dipole moment. The preparation of an ultracold quantum gas of polar molecules might therefore come within experimental reach.

physics.atom-ph↗

arXiv2007

Testing non-classical theories of electromagnetism with ion interferometry

We discuss using a table-top ion interferometer to search for deviations from Coulomb's inverse-square law. Such deviations would result from non-classical effects such at a non-zero photon rest mass. We discuss the theory behind the proposed measurement, explain which fundamental, experimentally controllable parameters are the relevant figures of merit, and calculate the expected performance of such a device in terms of these parameters. The sensitivity to deviations in the exponent of the inverse-square law is predicted to be a few times $10^{-22}$, an improvement by five orders of magnitude over current experiments. It could measure a non-zero photon rest mass smaller than $9\times10^{-50}$ grams, nearly 100 times smaller than current laboratory experiments.

physics.atom-ph↗