February 27
Speaker: Karen Michaeli, MIT
Title: "Probing interactions with thermal transport"
Abstract:
Thermal and thermoelectric conductivities are ideal probes of
interaction effects in correlated electron systems. This is because, in
contrast to an electric current, a heat current can be transmitted
also by neutral quasiparticles. For instance, energy can be carried by
excitations that mediate interactions between other quasiparticles. In
my talk I will present two examples of the dramatic effect of
interactions on thermal and thermoelectric transport phenomena. The
first is the Nernst effect in the vicinity of the superconducting phase
transition. I will demonstrate that the giant Nernst signal,
experimentally observed in amorphous films far above Tc, is caused by
the fluctuations of the superconducting order parameter. Moreover, I
will discuss the anomalous behavior of the Nernst effect near the
magnetic-field-induced quantum critical phase transition. The second
example is thermal conductivity in spin liquids. Spin liquids can form
in the vicinity of the Mott metal-insulator transition when the charge
is gapped while the spin degrees of freedom strongly fluctuate. These
low energy excitations, dubbed spinons, can conduct heat. The spinons
also exhibit a magnetic interaction that leads to non-Fermi liquid
behavior. I will show that even in the absence of disorder this strong
interaction provides an efficient relaxation mechanism for heat and spin
currents, keeping them finite at the lowest temperatures
May 1
Speaker: Julio Barreiro, Max Planck Institute of Quantum Optics & University of Munich, Germany
Title: “Harnessing additional degrees of freedom and the environment to experimentally enable quantum applications and simulations”
Abstract
Quantum simulations and applications of quantum information usually have
experimentally demanding requirements. I will show how these were
circumvented in several experiments with photons and ions by using
resources additional to the systems of interest. In particular, we take
advantage of other degrees of freedom and the environment, either
intrinsic or engineered, through dissipation and decoherence. As an
example, although full quantum dense coding is impossible with linear
optics, we realized it by using entanglement in an additional degree of
freedom of a pair of photons. Another challenging task is quantum error
correction. By dissipatively providing fresh ancillas to the algorithm, a
qubit was repetitively corrected for in three iterations in a system of
trapped ions. In the context of quantum simulations, an auxiliary qubit
was engineered as a controlled environment that allowed us to
demonstrate a toolbox for the simulation of open systems. Finally, I
will discuss how similar approaches can lead to an arbitrary many-body
simulator in a system of ultracold atoms in optical lattices.
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