Kaden R. A. Hazzard

Observation of dipolar spin-exchange interactions with lattice-confined polar molecules

With the recent production of polar molecules in the quantum regime [1, 2], long-range dipolar interactions are expected to facilitate the understanding of strongly interacting many-body quantum systems and to realize lattice spin models [3] for exploring quantum magnetism. In atomic systems, where interactions require wave function overlap, effective spin interactions on a lattice can be realized through superexchange; however, the coupling is relatively weak and limited to nearest-neighbor interactions [4–6]. In contrast, dipolar interactions exist even in the absence of tunneling and extend beyond nearest neighbors. This allows coherent spin dynamics to persist even for gases with relatively high entropy and low lattice filling. While measured effects of dipolar interactions in ultracold molecular gases have thus far been limited to the modification of inelastic collisions and chemical reactions [7, 8], we now report the first observation of dipolar interactions of polar molecules pinned in a three-dimensional optical lattice. We realize a lattice spin model where spin is encoded in rotational states of molecules that are prepared and probed by microwaves. This interaction arises from the resonant exchange of rotational angular momentum between two molecules and realizes a spin-exchange interaction. The dipolar interactions are apparent in the evolution of the spin coherence, where we observe clear oscillations in addition to an overall decay of the coherence. The frequency of these oscillations, the strong dependence of the spin coherence time on the lattice filling factor, and the effect of a multi-pulse sequence designed to reverse dynamics due to two-body exchange interactions all provide clear evidence of dipolar interactions. Furthermore, we demonstrate the suppression of loss in weak lattices due to a quantum Zeno mechanism [9]. Measurements of these tunneling-induced losses allow us to independently determine the lattice filling factor. The results reported here comprise an initial exploration of the behavior of many-body spin models with direct, long-range spin interactions and lay the groundwork for future studies of many-body dynamics in spin lattices.With the production of polar molecules in the quantum regime, long-range dipolar interactions are expected to facilitate understanding of strongly interacting many-body quantum systems and to realize lattice spin models for exploring quantum magnetism. In ordinary atomic systems, where contact interactions require wavefunction overlap, effective spin interactions on a lattice can be mediated by tunnelling, through a process referred to as superexchange; however, the coupling is relatively weak and is limited to nearest-neighbour interactions. In contrast, dipolar interactions exist even in the absence of tunnelling and extend beyond nearest neighbours. This allows coherent spin dynamics to persist even for gases with relatively high entropy and low lattice filling. Measured effects of dipolar interactions in ultracold molecular gases have been limited to the modification of inelastic collisions and chemical reactions. Here we use dipolar interactions of polar molecules pinned in a three-dimensional optical lattice to realize a lattice spin model. Spin is encoded in rotational states of molecules that are prepared and probed by microwaves. Resonant exchange of rotational angular momentum between two molecules realizes a spin-exchange interaction. The dipolar interactions are apparent in the evolution of the spin coherence, which shows oscillations in addition to an overall decay of the coherence. The frequency of these oscillations, the strong dependence of the spin coherence time on the lattice filling factor and the effect of a multipulse sequence designed to reverse dynamics due to two-body exchange interactions all provide evidence of dipolar interactions. Furthermore, we demonstrate the suppression of loss in weak lattices due to a continuous quantum Zeno mechanism. Measurements of these tunnelling-induced losses allow us to determine the lattice filling factor independently. Our work constitutes an initial exploration of the behaviour of many-body spin models with direct, long-range spin interactions and lays the groundwork for future studies of many-body dynamics in spin lattices.

Novel Dielectric Anomaly in the Hole-Doped La2Cu1 xLixO4 and La2 xSrxNiO4 Insulators: Signature of an Electronic Glassy State

Charge inhomogeneities in hole-doped oxides attractgreat interest, in part due to their possible relation tohigh temperature superconductivity. Perhaps the bestknown examples are stripes, wherein holes congregatealong lines which serve as domain boundaries in a sur-rounding antiferromagnetic environment. These werepredicted [1, 2] andobservedin Nd-doped La

A Novel Dielectric Anomaly in Cuprates and Nickelates: Signature of an Electronic Glassy State

Charge inhomogeneities in hole-doped oxides attractgreat interest, in part due to their possible relation tohigh temperature superconductivity. Perhaps the bestknown examples are stripes, wherein holes congregatealong lines which serve as domain boundaries in a sur-rounding antiferromagnetic environment. These werepredicted [1, 2] andobservedin Nd-doped La

Two-particle quantum interference in tunnel-coupled optical tweezers

Bosons of a feather flit together Bosons are a type of particle that likes to congregate. This property has a major effect on the behavior of identical bosons. Kaufman et al. demonstrated quantum interference of two bosonic Rb atoms placed in two neighboring quantum wells (see the Perspective by Thompson and Lukin). They prepared the atoms in exactly the same state so that there would be no way to tell them apart except for which well each atom was in. They then monitored the probability of the two atoms still being in separate wells. At certain times, the probability had a characteristic dip signifying that the bosons preferred to be in the same well. Science, this issue p. 306; see also p. 272 Two bosonic rubidium atoms in coupled quantum wells are prepared in a symmetrical state and allowed to interfere. [Also see Perspective by Thompson and Lukin] The quantum statistics of atoms is typically observed in the behavior of an ensemble via macroscopic observables. However, quantum statistics modifies the behavior of even two particles. Here, we demonstrate near-complete control over all the internal and external degrees of freedom of two laser-cooled 87Rb atoms trapped in two optical tweezers. This controllability allows us to observe signatures of indistinguishability via two-particle interference. Our work establishes laser-cooled atoms in optical tweezers as a promising route to bottom-up engineering of scalable, low-entropy quantum systems.A. M. Kaufman, 2 B. J. Lester, 2 C. M. Reynolds, 2 M. L. Wall, 2 M. Foss-Feig, K. R. A. Hazzard, 2 A. M. Rey, 2 and C. A. Regal 2 JILA, National Institute of Standards and Technology and University of Colorado Department of Physics, University of Colorado, Boulder, Colorado 80309, USA Joint Quantum Institute and the National Institute of Standards and Technology, Gaithersburg, Maryland, 20899, USA (Dated: June 18, 2014)

Far-from-Equilibrium Quantum Magnetism with Ultracold Polar Molecules

Recent theory has indicated how to emulate tunable models of quantum magnetism with ultracold polar molecules. Here we show that present molecule optical lattice experiments can accomplish three crucial goals for quantum emulation, despite currently being well below unit filling and not quantum degenerate. The first is to verify and benchmark the models proposed to describe these systems. The second is to prepare correlated and possibly useful states in well-understood regimes. The third is to explore many-body physics inaccessible to existing theoretical techniques. Our proposal relies on a nonequilibrium protocol that can be viewed either as Ramsey spectroscopy or an interaction quench. The proposal uses only routine experimental tools available in any ultracold molecule experiment. To obtain a global understanding of the behavior, we treat short times pertubatively, develop analytic techniques to treat the Ising interaction limit, and apply a time-dependent density matrix renormalization group to disordered systems with long range interactions.

Quantum correlations and entanglement in far-from-equilibrium spin systems

By applying complementary analytic and numerical methods, we investigate the dynamics of spin-

Suppressing the loss of ultracold molecules via the continuous quantum Zeno effect

\frac{1}{2} XXZ

Detection and Visualization of Anomalous Structures in Molecular Dynamics Simulation Data

models with variable-range interactions in arbitrary dimensions. The dynamics we consider is initiated from uncorrelated states that are easily prepared in experiments; it can be equivalently viewed as either Ramsey spectroscopy or a quantum quench. Our primary focus is the dynamical emergence of correlations and entanglement in these far-from-equilibrium interacting quantum systems: We characterize these correlations by the entanglement entropy, concurrence, and squeezing, which are inequivalent measures of entanglement corresponding to different quantum resources. In one spatial dimension, we show that the time evolution of correlation functions manifests a nonperturbative dynamic singularity. This singularity is characterized by a universal power-law exponent that is insensitive to small perturbations. Explicit realizations of these models in current experiments using polar molecules, trapped ions, Rydberg atoms, magnetic atoms, and alkaline-earth and alkali-metal atoms in optical lattices, along with the relative merits and limitations of these different systems, are discussed.

Topological phases in ultracold polar-molecule quantum magnets

We investigate theoretically the suppression of two-body losses when the on-site loss rate is larger than all other energy scales in a lattice. This work quantitatively explains the recently observed suppression of chemical reactions between two rotational states of fermionic KRb molecules confined in one-dimensional tubes with a weak lattice along the tubes [Yan et al., Nature (London) 501, 521 (2013)]. New loss rate measurements performed for different lattice parameters but under controlled initial conditions allow us to show that the loss suppression is a consequence of the combined effects of lattice confinement and the continuous quantum Zeno effect. A key finding, relevant for generic strongly reactive systems, is that while a single-band theory can qualitatively describe the data, a quantitative analysis must include multiband effects. Accounting for these effects reduces the inferred molecule filling fraction by a factor of 5. A rate equation can describe much of the data, but to properly reproduce the loss dynamics with a fixed fillingfraction for all lattice parameters we develop a mean-field model and benchmark it with numerically exacttime-dependent density matrix renormalization group calculations.

Quenching to unitarity: Quantum dynamics in a three-dimensional Bose gas

We explore techniques to detect and visualize features in data from molecular dynamics (MD) simulations. Although the techniques proposed are general, we focus on silicon (Si) atomic systems. The first set of methods use 3D location of atoms. Defects are detected and categorized using local operators and statistical modeling. Our second set of exploratory techniques employ electron density data. This data is visualized to glean the defects. We describe techniques to automatically detect the salient isovalues for isosurface extraction and designing transfer functions. We compare and contrast the results obtained from both sources of data. Essentially, we find that the methods of defect (feature) detection are at least as robust as those based on the exploration of electron density for Si systems.