



01444nas a2200169   4500008004100000245007500041210006900116260001500185490000600200520093200206100001701138700002201155700001901177700001901196700002201215856003701237       2018                        eng d00aObservation of bound state self-interaction in a nano-eV atom collider0 aObservation of bound state selfinteraction in a nanoeV atom coll  c2018/11/200 v93 a<p>Quantum mechanical scattering resonances for colliding particles occur when a continuum scattering state couples to a discrete bound state between them. The coupling also causes the bound state to interact with itself via the continuum and leads to a shift in the bound state energy, but, lacking knowledge of the bare bound state energy, measuring this self-energy via the resonance position has remained elusive. Here, we report on the direct observation of self-interaction by using a nano-eV atom collider to track the position of a magnetically-tunable Feshbach resonance through a parameter space spanned by energy and magnetic field. Our system of potassium and rubidium atoms displays a strongly non-monotonic resonance trajectory with an exceptionally large self-interaction energy arising from an interplay between the Feshbach bound state and a different, virtual bound state at a fixed energy near threshold.</p>1 aThomas, Ryan1 aChilcott, Matthew1 aTiesinga, Eite1 aDeb, Amita, B.1 aKjærgaard, Niels  uhttps://arxiv.org/abs/1807.0117401661nas a2200121   4500008004100000245009700041210006900138520123700207100001301444700001901457700002601476856003701502       2018                        eng d00aOrbital quantum magnetism in spin dynamics of strongly interacting magnetic lanthanide atoms0 aOrbital quantum magnetism in spin dynamics of strongly interacti3 a<p>Laser cooled lanthanide atoms are ideal candidates with which to study strong and unconventional quantum magnetism with exotic phases. Here, we use state-of-the-art closed-coupling simulations to model quantum magnetism for pairs of ultracold spin-6 erbium lanthanide atoms placed in a deep optical lattice. In contrast to the widely used single-channel Hubbard model description of atoms and molecules in an optical lattice, we focus on the single-site multi-channel spin evolution due to spin-dependent contact, anisotropic van der Waals, and dipolar forces. This has allowed us to identify the leading mechanism, orbital anisotropy, that governs molecular spin dynamics among erbium atoms. The large magnetic moment and combined orbital angular momentum of the 4f-shell electrons are responsible for these strong anisotropic interactions and unconventional quantum magnetism. Multi-channel simulations of magnetic Cr atoms under similar trapping conditions show that their spin-evolution is controlled by spin-dependent contact interactions that are distinct in nature from the orbital anisotropy in Er. The role of an external magnetic field and the aspect ratio of the lattice site on spin dynamics is also investigated.</p>1 aLi, Ming1 aTiesinga, Eite1 aKotochigova, Svetlana  uhttps://arxiv.org/abs/1804.1010201328nas a2200157   4500008004100000245008400041210006900125260001500194300001100209490000700220520085400227100001801081700001901099700001501118856003701133       2015                        eng d00aOptimization of collisional Feshbach cooling of an ultracold  nondegenerate gas0 aOptimization of collisional Feshbach cooling of an ultracold non  c2015/04/20  a0436260 v913 a  We optimize a collision-induced cooling process for ultracold atoms in the
nondegenerate regime. It makes use of a Feshbach resonance, instead of rf
radiation in evaporative cooling, to selectively expel hot atoms from a trap.
Using functional minimization we analytically show that for the optimal cooling
process the resonance energy must be tuned such that it linearly follows the
temperature. Here, optimal cooling is defined as maximizing the phase-space
density after a fixed cooling duration. The analytical results are confirmed by
numerical Monte-Carlo simulations. In order to simulate more realistic
experimental conditions, we show that background losses do not change our
conclusions, while additional non-resonant two-body losses make a lower initial
resonance energy with non-linear dependence on temperature preferable.
1 aNuske, Marlon1 aTiesinga, Eite1 aMathey, L.  uhttp://arxiv.org/abs/1412.8473v1