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arXiv:1506.02496 · Physical Review A

Magnetically tunable Feshbach resonances in Li+Er

Maykel Leonardo González-Martínez, Piotr Szymon Żuchowski

Published Aug 24, 2015• 25 citations
arXivHTMLPDF

Abstract

We explore the magnetic Feshbach spectra of ultracold ground-state Li+Er systems. Our calculations predict many tunable resonances at fields below 1000 G that could be stably tuned in ultracold experiments. We show that Li+Er spectra are much less congested than those of systems involving heavier highly magnetic atoms and exhibit nonchaotic properties. These features would facilitate identifying and addressing individual resonances. We derive a simple model for the mass-scaling shifting of low-field resonances that may simplify designing experiments with different Er bosonic isotopes. Our work establishes Li+Er as very promising systems for quantum simulation, precision measurements and the formation of polar paramagnetic molecules.

DOI
10.1103/physreva.92.022708

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•Jan 1, 2013•0 citations
We explore the magnetic Feshbach spectra of ultracold ground-state Li+Er systems. Our calculations predict many tunable resonances at fields below 1000 G that could be stably tuned in ultracold experiments. We show that Li+Er spectra are much less congested than those of systems involving heavier highly magnetic atoms and exhibit nonchaotic properties. These features would facilitate identifying and addressing individual resonances. We derive a simple model for the mass-scaling shifting of low-field resonances that may simplify designing experiments with different Er bosonic isotopes. Our work establishes Li+Er as very promising systems for quantum simulation, precision measurements and the formation of polar paramagnetic molecules.
We investigate the possibility of forming Li+Yb ultracold molecules by magnetoassociation in mixtures of ultracold atoms. We find that magnetically tunable Feshbach resonances exist, but are extremely narrow for even-mass ytterbium isotopes, which all have zero spin. For odd-mass Yb isotopes, however, there is a new mechanism due to hyperfine coupling between the electron spin and the Yb nuclear magnetic moment. This mechanism produces Feshbach resonances for fermionic Yb isotopes that can be more than 2 orders of magnitude larger than for the bosonic counterparts.
We report on the experimental observation of Feshbach resonances in large-mass-imbalance mixtures of erbium (Er) and lithium (Li). All combinations of 168Er,166Er^{168}\mathrm{Er}, ^{166}\mathrm{Er}168Er,166Er, and 7Li,6Li^{7}\mathrm{Li}, ^{6}\mathrm{Li}7Li,6Li are cooled to temperatures of a few microkelvin, partially by means of sympathetic cooling together with ytterbium (Yb) as a third mixture component. The Er-Li inelastic interspecies collisional properties are studied for magnetic fields up to 680G680\phantom{\rule{0.28em}{0ex}}\mathrm{G}680G. In all cases, resonant interspecies loss features, indicative of Feshbach resonances, have been observed. While most resonances have sub-Gauss widths, a few of them are broad and feature widths of several Gauss. Those broad resonances are a key to the realization of ultracold Er-Li quantum gas mixtures with tunable interactions.
Abstract We investigate ultracold magnetic-field-assisted collisions in the so far unexplored ErYb system. The nonsphericity of the Er atom leads to weakly anisotropic interactions that provide the mechanism for Feshbach resonances to emerge. The resonances are moderately sparsely distributed with a density of 0.1–0.3 G−1 and exhibit chaotic statistics characterized by a Brody parameter η ≈ 0.5–0.7. The chaotic behaviour of Feshbach resonances is accompanied by strong mixing of magnetic and rotational quantum numbers in near-threshold bound states. We predict the existence of broad resonances at fields < 300 G that may be useful for the precise control of scattering properties and magnetoassociation of ErYb molecules. The high number of bosonic Er–Yb isotopic combinations gives many opportunities for mass scaling of interactions. Uniquely, two isotopic combinations have nearly identical reduced masses (differing by less than 10−5 relative) that we expect to have strikingly similar Feshbach resonance spectra, which would make it possible to experimentally measure their sensitivity to hypothetical variations of proton-to-electron mass ratio.
Quantum gases of doubly polar molecules represent appealing frameworks for a variety of cross-disciplinary applications, encompassing quantum simulation and computation, controlled quantum chemistry, and precision measurements. Through a joint experimental and theoretical study, here we explore a novel class of ultracold paramagnetic polar molecules combining lithium alkali and chromium transition metal elements. Focusing on the specific bosonic isotopologue 6 Li 53 Cr , leveraging on the Fermi statistics of the parent atomic mixture and on suitable Feshbach resonances recently discovered, we produce up to 50 × 10 3 ultracold Li Cr molecules at peak phase-space densities exceeding 0.1, prepared within the least bound rotationless level of the Li Cr electronic ground state X 6 Σ + . By also developing new probing methods, we thoroughly characterize the molecular gas, demonstrating the paramagnetic nature of Li Cr dimers and the precise control of their quantum state. We investigate their stability against inelastic processes and identify a parameter region where pure Li Cr samples exhibit lifetimes exceeding 0.2 s. Parallel to this, we employ state-of-the-art quantum chemical calculations to accurately predict the properties of Li Cr ground and excited electronic states. This model, able to reproduce the experimental Li - Cr high-spin, scattering length, allows us to identify both efficient paths to coherently transfer weakly bound Li Cr dimers to their absolute ground state, and suitable transitions for their subsequent optical manipulation. Our studies establish Li - Cr as a prime candidate to realize ultracold gases of doubly polar molecules with significant electric (3.3 D) and magnetic ( 5 μ B ) dipole moments. Published by the American Physical Society 2024
We investigate ultracold collisions in a novel mixture of ^{6}Li and ^{53}Cr fermionic atoms, discovering more than 50 interspecies Feshbach resonances via loss spectroscopy. Building a full coupled-channel model, we unambiguously characterize the ^{6}Li-^{53}Cr scattering properties and yield predictions for other isotopic pairs. In particular, we identify various Feshbach resonances that enable the controlled tuning of elastic s- and p-wave ^{6}Li-^{53}Cr interactions. Our studies thus make lithium-chromium mixtures emerge as optimally suited platforms for the experimental search of elusive few- and many-body regimes of highly correlated fermionic matter, and for the realization of a new class of ultracold polar molecules possessing both electric and magnetic dipole moments.
Trapped cold atoms at very low temperatures, now readily accessible experimentally, can be controlled and serve as a testing ground for many theoretical physical properties which are paralleled in condensed matter systems. Ultracold trapped atom experiments show promise to recreate analogous condensed matter systems in a controlled environment and to create novel many-body quantum states of matter. The tunability of trapping laser intensities and magnetically controlled Feshbach interactions are the main tools for varying lattice hopping strengths and inter-particle interactions. In this thesis, we search for the phase of a many-body system of cold fermion atoms that can convert to boson molecules and vice versa. We then look at the microscopic details of two atoms that interact to form a quasibound molecule. Our two-atom model explains the mechanism behind the magnetically tunable interparticle interaction known as the Feshbach resonance. We find a dependence of the bound pair formation on the two-particle energy. Our results show that if a magnetic field can be fine tuned to sufficient precision, of order 10 mG, a narrow resonance can be achieved where longer lived bound states can be created. This narrow resonance reconciliates the two-body physics with the effective Hamiltonian that describes the many-body system.