7,781 research outputs found
Primary thermometry triad at 6 mK in mesoscopic circuits
Quantum physics emerge and develop as temperature is reduced. Although
mesoscopic electrical circuits constitute an outstanding platform to explore
quantum behavior, the challenge in cooling the electrons impedes their
potential. The strong coupling of such micrometer-scale devices with the
measurement lines, combined with the weak coupling to the substrate, makes them
extremely difficult to thermalize below 10 mK and imposes in-situ thermometers.
Here we demonstrate electronic quantum transport at 6 mK in micrometer-scale
mesoscopic circuits. The thermometry methods are established by the comparison
of three in-situ primary thermometers, each involving a different underlying
physics. The employed combination of quantum shot noise, quantum back-action of
a resistive circuit and conductance oscillations of a single-electron
transistor covers a remarkably broad spectrum of mesoscopic phenomena. The
experiment, performed in vacuum using a standard cryogen-free dilution
refrigerator, paves the way toward the sub-millikelvin range with additional
thermalization and refrigeration techniques.Comment: Article and Supplementar
Vortex and gap generation in gauge models of graphene
Effective quantum field theoretical continuum models for graphene are
investigated. The models include a complex scalar field and a vector gauge
field. Different gauge theories are considered and their gap patterns for the
scalar, vector, and fermion excitations are investigated. Different gauge
groups lead to different relations between the gaps, which can be used to
experimentally distinguish the gauge theories. In this class of models the
fermionic gap is a dynamic quantity. The finite-energy vortex solutions of the
gauge models have the flux of the "magnetic field" quantized, making the
Bohm-Aharonov effect active even when external electromagnetic fields are
absent. The flux comes proportional to the scalar field angular momentum
quantum number. The zero modes of the Dirac equation show that the gauge models
considered here are compatible with fractionalization
Anomalous dynamics of cell migration
Cell movement, for example during embryogenesis or tumor metastasis, is a
complex dynamical process resulting from an intricate interplay of multiple
components of the cellular migration machinery. At first sight, the paths of
migrating cells resemble those of thermally driven Brownian particles. However,
cell migration is an active biological process putting a characterization in
terms of normal Brownian motion into question. By analyzing the trajectories of
wildtype and mutated epithelial (MDCK-F) cells we show experimentally that
anomalous dynamics characterizes cell migration. A superdiffusive increase of
the mean squared displacement, non-Gaussian spatial probability distributions,
and power-law decays of the velocity autocorrelations are the basis for this
interpretation. Almost all results can be explained with a fractional Klein-
Kramers equation allowing the quantitative classification of cell migration by
a few parameters. Thereby it discloses the influence and relative importance of
individual components of the cellular migration apparatus to the behavior of
the cell as a whole.Comment: 20 pages, 3 figures, 1 tabl
Josephson dynamics for coupled polariton modes under the atom-field interaction in the cavity
We consider a new approach to the problem of Bose-Einstein condensation (BEC)
of polaritons for atom-field interaction under the strong coupling regime in
the cavity. We investigate the dynamics of two macroscopically populated
polariton modes corresponding to the upper and lower branch energy states
coupled via Kerr-like nonlinearity of atomic medium. We found out the
dispersion relations for new type of collective excitations in the system under
consideration. Various temporal regimes like linear (nonlinear) Josephson
transition and/or Rabi oscillations, macroscopic quantum self-trapping (MQST)
dynamics for population imbalance of polariton modes are predicted. We also
examine the switching properties for time-averaged population imbalance
depending on initial conditions, effective nonlinear parameter of atomic medium
and kinetic energy of low-branch polaritons.Comment: 10 pages, 6 postscript figures, uses svjour.cl
Bosonic Anomalies, Induced Fractional Quantum Numbers and Degenerate Zero Modes: the anomalous edge physics of Symmetry-Protected Topological States
The boundary of symmetry-protected topological states (SPTs) can harbor new
quantum anomaly phenomena. In this work, we characterize the bosonic anomalies
introduced by the 1+1D non-onsite-symmetric gapless edge modes of 2+1D bulk
bosonic SPTs with a generic finite Abelian group symmetry (isomorphic to
). We
demonstrate that some classes of SPTs (termed "Type II") trap fractional
quantum numbers (such as fractional charges) at the 0D kink of the
symmetry-breaking domain walls; while some classes of SPTs (termed "Type III")
have degenerate zero energy modes (carrying the projective representation
protected by the unbroken part of the symmetry), either near the 0D kink of a
symmetry-breaking domain wall, or on a symmetry-preserving 1D system
dimensionally reduced from a thin 2D tube with a monodromy defect 1D line
embedded. More generally, the energy spectrum and conformal dimensions of
gapless edge modes under an external gauge flux insertion (or twisted by a
branch cut, i.e., a monodromy defect line) through the 1D ring can distinguish
many SPT classes. We provide a manifest correspondence from the physical
phenomena, the induced fractional quantum number and the zero energy mode
degeneracy, to the mathematical concept of cocycles that appears in the group
cohomology classification of SPTs, thus achieving a concrete physical
materialization of the cocycles. The aforementioned edge properties are
formulated in terms of a long wavelength continuum field theory involving
scalar chiral bosons, as well as in terms of Matrix Product Operators and
discrete quantum lattice models. Our lattice approach yields a regularization
with anomalous non-onsite symmetry for the field theory description. We also
formulate some bosonic anomalies in terms of the Goldstone-Wilczek formula.Comment: 29 pages, 12 Figures. v3 clarification to be accessible for both HEP
and CMT. Thanks to Roman Jackiw for introducing new Ref
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