USC
Quantum Information, Condensed Matter and Biophysics Seminars
These seminars are scheduled on Fridays at 2:00pm, and the
location is SSL 150, unless otherwise noted. Some of the seminars
will be held jointly with UCLA and CALTECH.
For more information contact Lorenzo Campos Venuti (condensed
matter) or Ben Reichardt
(quantum information).
Fall 2014
November 21 (2014), 2pm SSL 150 Nikhil Malvankar (UMass) Seeing is Believing: Imaging Charge Flow along Bacterial Proteins Reveals A Novel Mechanism of Biological Electron Transport
Electron
flow in biologically proteins generally occurs via tunneling or
hopping mechanism and the possibility of electron delocalization or
metal-like conductivity has been considered previously impossible. In
this colloquium, I will present our recent studies on protein
nanofilaments, pili, secreted by a common soil microorganism
Geoabacter
sulfurreducens,
that challenge this long-standing belief. Using a scanning probe
microscopy-based nanoscopic approach to visualize charge propagation
in native biomolecules, we have found out that pili propagate charges
in a manner similar to metallic carbon nanotubes [1].
Conductive
pili enable Geobacter
to export electrons outside their body to carry out respiration [2]
and
cell-to-cell electron exchange [3]
over
several micrometers using direct electrical connections. I will
discuss our fundamental studies as well as potential applications and
bioelectronic devices using this new class of electronically
functional proteins.
[1] Malvankar et al.
Nature Nanotechnology, (2014) DOI:
10.1038/NNANO.2014.236
[2] Malvankar et al.
Nature Nanotechnology, 6, 573 (2011)
[3] Summers,
Fogarty, Leang, Franks, Malvankar and Lovley. Science,
330, 1413 (2010)
December 5 (2014), 2pm SSL150 Angelo Bassi, University of Trieste Models of spontaneous wave function collapse: what they are and how they can be tested There are few proposals, which
explicitly allow for (experimentally testable) deviations from standard
quantum theory. Models of spontaneous wave function collapse (collapse
models) are among the most-widely studied proposals of this kind. The
Schroedinger equation is modified by including nonlinear and stochastic
terms, which describe the collapse of the wave function in space. These
spontaneous collapses are “rare” for macroscopic systems, hence their
quantum properties are left almost unaltered. On the other hand,
collapses become more and more frequent, the larger the object, to the
point that macroscopic superpositions are rapidly suppressed. I will
briefly review the main features of collapse models. Then I will
present promising experimental tests, ranging from cosmological
observations, to matter-wave interferometry, to optomechanics, to
spectroscopy.
December 12 (2014), 2pm SSL150 Bill Kaminsky (MIT) Diabatic Quantum Computation – Why it Might Not Really Pay to Go for the “A”? In this talk, we argue that the time has come to consider how well an adiabatic quantum computer
approximates problems when it degrades into following not its instantaneous ground state, but rather the
diabatic continuation of its initial ground state. In other words, we argue the time has come to ask:
How
low an energy does one achieve in the spectrum of the final, problem
Hamiltonian if one is going sufficiently fast that at every avoided
crossing one takes upper branch rather than
the lower branch, but not so fast that one induces any notable
excitation away from avoided crossings?
Moreover, we argue that the time has come to ask
this question not merely because there are a mounting bodies of
theoretical, numerical, and experimental evidence that an adiabatic
quantum computer generically cannot supply an
exponential speedup on exactly solving instances of NP-hard problems while there is a quite paltry body of evidence on how much it can speedup
approximation of such instances to high accuracy.
Rather, we argue the time has come because we actually possess tools
--- namely, high-order perturbation theory around the initial
Hamiltonian extended by Hermite-Padé interpolation at avoided
crossings --- with which we should be able to make substantial progress
on question of how good an approximation the diabatic continuation of
the initial ground state provides. In closing, we also discuss progress
on understanding how fast an adiabatic quantum
computer can approximate NP-hard problem instances when it faces the
practical constraint of operating at a constant temperature that cannot
shrink as the instance sizes grow. Specifically, we describe a
stand-alone result about a moment-based method to upper-bound
how many energy eigenstates are within O(1) energy of a
given energy eigenstate in the lowest part of the spectrum at a generic
point in an adiabatic quantum computer’s interpolation. More seminars
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