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Уважаемые сотрудники ИТФ,<br>
<br>
В пятницу 20 декабря состоится 2 коллоквиума.<br>
<br>
На Ученом совете в 11:30 будет заслушан доклад :<br>
<br>
Joerg Schmalian (Karlsruhe Institute of Technology)<br>
<font size="+1"><b>Ordered fluctuations: about vestigial order in
quantum materials</b></font><br>
<br>
A hallmark of the phase diagrams of quantum materials is the
existence of multiple electronic ordered states. In many cases those
are not independent, competing phases, but instead display a complex
intertwinement. In this talk, we focus on a realization of
intertwined orders with a fluctuation-driven vestigial phase
characterized by a composite order parameter. In other words, we are
investigating the condensation of fluctuations.<br>
We demonstrate that this concept naturally explains the nematic
state in iron-based superconductors and nematic superconductivity in
doped topological insulators. In addition we propose a natural
mechanism for charge 4e superconductivity with half flux quanta. We
present a formalism that provides a framework to understand the
complexity of quantum materials based on symmetry, largely without
resorting to microscopic models. <br>
<br>
<br>
В 15:00 будет заслушан доклад :<br>
<br>
Vadim Smelyanskiy (Google, Los Angeles)<br>
<font size="+1"><b>Non-ergodic delocalized states for efficient
population transfer within a narrow band of the energy landscape</b></font><br>
<br>
<div class="abstract tex">
We will review the advances and challenges in the field of quantum
combinatorial optimization and closely related problem of
low-energy eigenstates and coherent dynamics in transverse field
quantum spin glass models. We will discuss the role of collective
spin tunneling that gives rise to bands of delocalized non-ergodic
quantum states providing the coherent pathway for the population
transfer (PT) algorithm: the quantum evolution under a constant
transverse field that starts at a low-energy spin configuration
and ends up in a superposition of spin configurations inside a
narrow energy window. We study the transverse field induced
quantum dynamics of the following spin model: zero energy of all
spin configurations except for a small fraction of spin
configuration that form a narrow band at large negative energy. We
use the cavity method for heavy-tailed random matrices to obtain
the statistical properties of the low-energy eigenstates in an
explicit analytical form. In a broad interval of transverse
fields, they are non-ergodic, albeit extended giving rise to a
qualitatively new type of quantum dynamics. For large transverse
fields »1 the typical runtime of PT algorithm <span
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scales with n and Ω as that of the Grover’s quantum search, except
for the small correction to the exponent θ ≈ 1/(2). The model we
consider is non-integrable. As a result, our PT protocol does not
require any fine-tuning of and may be initialized in a computational
basis state. We argue that our approach can be applied to study PT
protocol in other optimization problems with the potential quantum
advantage over classical algorithms.<br>
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