Eric Sembrat's Test Bonanza

While we would like to avoid frustration in our daily lives, frustration in condensed matter produces novel phenomena with important consequences. Materials that are geometrically frustrated cannot minimize the energy of every particle-particle interaction, even in their ground state; materials that are kinetically frustrated are trapped out of equilibrium, i.e., they cannot reach their ground state. In this talk I will review a series of experiments I have performed investigating the role of frustration in the assembly and phase behavior of colloidal systems. By tuning particle size, shape, and confinement, I systematically varied the degree of frustration in each experiment. This controlled approach enabled me to create geometrically frustrated colloidal "antiferromagnets," to observe the competition between crystallization and vitrification, and to learn how glasses age. These concepts also appeared in other non-equilibrium soft condensed matter experiments, from materials assembled on the surface of drying drops, to the directed assembly of protein-based structures.

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The Nuclear Spectroscopic Telescope Array, the first focusing high-energy X-ray (3 – 79 keV) telescope in orbit, extends sensitive X-ray observations above the band pass where Chandra and XMM-Newton operate. With an unprecedented combination of sensitivity, spectral and imaging resolution above 10 keV, NuSTAR is advancing our understanding of black holes, neutron stars, and supernova remnants. I will describe the mission, and present science highlights from the two-year baseline mission.

The existence of dark matter was first postulated by Jan Oort in1932 to account for the orbital velocities of stars in the Milky Way. Since that time, astrophysicists and astronomers have produced compelling evidence for the existence of dark matter and determined that it constitutes the bulk of the matter in the Universe. Despite this fact, the composition of the dark matter remains unknown. One compelling candidate for particle dark matter is the Weakly Interacting Massive Particle (WIMP). Working in a low-background environment in the Soudan Mine, located in northern Minnesota, the SuperCDMS experiment is designed to directly detect interactions between WIMPs and nuclei in its target Ge crystals. In this talk I will present the latest results from the SuperCDMS experiment. I will also discuss the current status of the SuperCDMS at Soudan experiment and plans for a future 50-kg scale experiment which is slated for operation in SNOLAB.

A fascinating manifestation of collective quantum phenomena in condensed matter is the emergence of elementary excitations – or quasiparticles – carrying quantum numbers that are fractions of those of a non-interacting system. Low-dimensional and frustrated magnetic materials, built from localized spins 1/2, display a diversity of such many-body phenomena. Moreover, they allow detailed experimental investigations, quantitative comparisons with theoretical predictions, and often surprise with counter-intuitive properties that are difficult to predict a-priori.

In this talk, I will present neutron scattering experiments that provide access to the dynamic spin correlations of one-dimensional (1D), square-lattice and triangular-lattice Heisenberg antiferromagnets. These results highlight the importance of understanding quantum fluctuations and interactions to describe the spin dynamics of some of the most fundamental models in magnetism. Starting from the 1D limit, I will first illustrate the concept of deconfined fractional spin excitations – or spinons – through their observation as pairs and quartets in single-crystals of copper sulfate [1]. Then, I will present on-going progresses made in the search for fractional spin excitations in bulk two-dimensional materials with and without geometric magnetic frustration. Throughout my talk, I shall stress the importance of combined efforts between materials discovery and characterisation, advanced spectroscopy, and theory, in the quest for new quantum states of matter.

 [1] ``Fractional spinon excitations in the quantum Heisenberg antiferromagnetic chain’’, M. Mourigal, M. Enderle, A. Klöpperpieper, J.-S. Caux, A. Stunault, H. M. Rønnow, Nature Physics 9, 435-441 (2013).

I will present time-resolved measurements of the relaxation dynamics, in a small molecular system, following ultraviolet (UV) photoexcitation. We probe these excitations through photoionization and velocity map imaging (VMI) spectroscopy. Vacuum and extreme ultraviolet (VUV/XUV) pump and probe pulses are created by exploiting strong-field high harmonic generation (HHG) from our state-of-the-art 30 mJ, 1 kHz laser system. Three dimensional photoelectron and photoion momentum images recorded with our VMI spectrometer reveal non-Born Oppenheimer dynamics in the vicinity of a conical intersection, and allow us track the state of the system as a function of time. I will also present a series of experiments developing techniques for studying molecular dynamics at fourth generation, free electron laser (FEL), light sources.

I will present two examples in which ‘fictitious fields’ lead to surprising photonic effects that would be difficult (if not impossible) to achieve with real fields.  Firstly, I will present the first observation of the topological protection of light - a ‘Photonic Floquet Topological Insulator’ [1].  The structure is an array of coupled helical waveguides (the helicity generates a fictitious circularly-polarized electric field that leads to the TI behavior).  Second, I will demonstrate artificial magnetic fields (‘pseudomagnetism’) in photonic lattices [2]. The pseudomagnetic field is generated by inhomogeneously straining the system (thus breaking periodicity), and leads to photonic Landau levels with very high photonic density of states.  Potential applications include robust photonic devices and strong light-matter interaction over large areas.

[1] Rechtsman, M. C. et al. Nature 496, 196–200 (2013).

[2] Rechtsman, M. C. et al. Nature Photon. 7, 153–158 (2013).

The manipulation and detection of individual quantum excitations forms the basis of modern quantum optics experiments. However, most of these experiments have been restricted to systems composed of only a few particles.

In recent years, tremendous experimental progress has been made in probing strongly interacting many-body systems at the level of individual particles. This was achieved using single-site- and single-atom-resolved imaging and manipulation of quantum gases in optical lattices. With this technique, ‘snapshots’ of a fluctuating many-body system are obtained, where individual excitations are directly visible and, by shining light through the imaging system, are also directly addressable.

I will review these developments and present, in more detail, a few chosen experiments: The single-site-resolved detection of correlation functions [1], the observation of the quantum dynamics of a mobile spin impurity [2], and the detection of an amplitude ‘Higgs’ mode [3]. I will conclude with analyzing the current limitations and possible future developments, in particular, concerning the detection of entanglement in quantum many-body systems.

[1] M. Endres, M. Cheneau, T. Fukuhara, C. Weitenberg, P. Schauss, C. Gross, L. Mazza, M. C. Banuls, L. Pollet, I. Bloch and S. Kuhr, Observation of Correlated Particle-Hole Pairs and String Order in Low-Dimensional Mott Insulators, Science 334, 200 (2011)

[2] T. Fukuhara, A. Kantian, M. Endres, M. Cheneau, P. Schauss, S. Hild, D. Bellem, U. Schollwock, T. Giamarchi, C. Gross, I. Bloch and S. Kuhr, Quantum dynamics of a mobile spin impurity, Nature Phys. 9, 235 (2013)

[3] M. Endres, T. Fukuhara, D. Pekker, M. Cheneau, P. Schauss, C. Gross, E. Demler, S. Kuhr, I. Bloch, The `Higgs' amplitude mode at the two-dimensional superfluid/Mott insulator transition, Nature 487, 454-458 (2012) 

Advances of quantum control in atomic and optical physics have made it possible to study intriguing phenomena originally discussed in condensed matter, nuclear, and gravitational physics. In quantum gas experiments, new insights are derived from out-of-equilibrium dynamics of novel quantum many-body phases. In the first part of my talk, I will present the observation of Sakharov oscillations in a quenched atomic superfluid. Sakharov acoustic oscillations, conventionally discussed in the context of early universe evolution and the temperature anisotropy of cosmic microwave background radiation, are a consequence of the interference of acoustic waves synchronously generated in an ideal fluid. I will describe how a quenched atomic superfluid provides unique opportunities to explore analogue physics in cosmology and gravity.

Moving toward a “brighter” future of an atomic quantum simulator, one exciting frontier is the integration of nanophotonics and atomic physics. I will present recent development of the first integrated optical circuit with new possibilities for studying novel quantum transport and many-body phenomena by way of photon-mediated atomic interactions.