7,859 research outputs found
Generating topological order from a 2D cluster state using a duality mapping
In this paper we prove, extend and review possible mappings between the
two-dimensional Cluster state, Wen's model, the two-dimensional Ising chain and
Kitaev's toric code model. We introduce a two-dimensional duality
transformation to map the two-dimensional lattice cluster state into the
topologically-ordered Wen model. Then, we subsequently investigates how this
mapping could be achieved physically, which allows us to discuss the rate at
which a topologically ordered system can be achieved. Next, using a lattice
fermionization method, Wen's model is mapped into a series of one-dimensional
Ising interactions. Considering the boundary terms with this mapping then
reveals how the Ising chains interact with one another. The relationships
discussed in this paper allow us to consider these models from two different
perspectives: From the perspective of condensed matter physics these mappings
allow us to learn more about the relation between the ground state properties
of the four different models, such as their entanglement or topological
structure. On the other hand, we take the duality of these models as a starting
point to address questions related to the universality of their ground states
for quantum computation.Comment: 5 Figure
The locations of features in the mass distribution of merging binary black holes are robust against uncertainties in the metallicity-dependent cosmic star formation history
New observational facilities are probing astrophysical transients such as
stellar explosions and gravitational wave (GW) sources at ever increasing
redshifts, while also revealing new features in source property distributions.
To interpret these observations, we need to compare them to predictions from
stellar population models. Such models require the metallicity-dependent cosmic
star formation history () as an input. Large uncertainties
remain in the shape and evolution of this function. In this work, we propose a
simple analytical function for . Variations of this function
can be easily interpreted, because the parameters link to its shape in an
intuitive way. We fit our analytical function to the star-forming gas of the
cosmological TNG100 simulation and find that it is able to capture the main
behaviour well. As an example application, we investigate the effect of
systematic variations in the parameters on the predicted
mass distribution of locally merging binary black holes (BBH). Our main
findings are: I) the locations of features are remarkably robust against
variations in the metallicity-dependent cosmic star formation history, and II)
the low mass end is least affected by these variations. This is promising as it
increases our chances to constrain the physics that governs the formation of
these objects.Comment: Submitted to ApJ, made with showyourwork, code available at
https://github.com/LiekeVanSon/SFRD_fi
Mechanisms of spin-polarized current-driven magnetization switching
The mechanisms of the magnetization switching of magnetic multilayers driven
by a current are studied by including exchange interaction between local
moments and spin accumulation of conduction electrons. It is found that this
exchange interaction leads to two additional terms in the
Landau-Lifshitz-Gilbert equation: an effective field and a spin torque. Both
terms are proportional to the transverse spin accumulation and have comparable
magnitudes
Pulsational pair-instability supernovae in gravitational-wave and electromagnetic transients
Current observations of binary black-hole ({BBH}) merger events show support
for a feature in the primary BH-mass distribution at
, previously interpreted as a signature of
pulsational pair-instability (PPISN) supernovae. Such supernovae are expected
to map a wide range of pre-supernova carbon-oxygen (CO) core masses to a narrow
range of BH masses, producing a peak in the BH mass distribution. However,
recent numerical simulations place the mass location of this peak above
. Motivated by uncertainties in the progenitor's
evolution and explosion mechanism, we explore how modifying the distribution of
BH masses resulting from PPISN affects the populations of gravitational-wave
(GW) and electromagnetic (EM) transients. To this end, we simulate populations
of isolated {BBH} systems and combine them with cosmic star-formation rates.
Our results are the first cosmological BBH-merger predictions made using the
\textsc{binary\_c} rapid population synthesis framework. We find that our
fiducial model does not match the observed GW peak. We can only explain the
peak with PPISNe by shifting the expected CO core-mass
range for PPISN downwards by . Apart from being
in tension with state-of-the art stellar models, we also find that this is
likely in tension with the observed rate of hydrogen-less super-luminous
supernovae. Conversely, shifting the mass range upward, based on recent stellar
models, leads to a predicted third peak in the BH mass function at
. Thus we conclude that the
feature is unlikely to be related to PPISNe.Comment: Accepted for publication in MNRAS. 19 pages, 8 figures includings
appendice
No peaks without valleys: The stable mass transfer channel for gravitational-wave sources in light of the neutron star-black hole mass gap
Gravitational-wave (GW) detections are starting to reveal features in the
mass distribution of double compact objects. The lower end of the black hole
(BH) mass distribution is especially interesting as few formation channels
contribute here and because it is more robust against variations in the cosmic
star formation than the high mass end. In this work we explore the stable mass
transfer channel for the formation of GW sources with a focus on the low-mass
end of the mass distribution. We conduct an extensive exploration of the
uncertain physical processes that impact this channel. We note that, for
fiducial assumptions, this channel reproduces the peak at in the GW-observed binary BH mass distribution remarkably
well, and predicts a cutoff mass that coincides with the upper edge of the
purported neutron star BH mass gap. The peak and cutoff mass are a consequence
of unique properties of this channel, namely (1) the requirement of stability
during the mass transfer phases, and (2) the complex way in which the final
compact object masses scale with the initial mass. We provide an analytical
expression for the cutoff in the primary component mass and show that this
adequately matches our numerical results. Our results imply that selection
effects resulting from the formation channel alone can provide an explanation
for the purported neutron star--BH mass gap in GW detections. This provides an
alternative to the commonly adopted view that the gap emerges during BH
formation.Comment: Accepted for publication in ApJ associated code is available at
https://github.com/LiekeVanSon/LowMBH_and_StableChanne
Spin accumulation induced resistance in mesoscopic ferromagnet/ superconductor junctions
We present a description of spin-polarized transport in mesoscopic
ferromagnet-superconductor (F/S) systems, where the transport is diffusive, and
the interfaces are transparent. It is shown that the spin reversal associated
with Andreev reflection generates an excess spin density close to the F/S
interface, which leads to a spin contact resistance. Expressions for the
contact resistance are given for two terminal and four terminal geometries. In
the latter the sign depends on the relative magnetization of the ferromagnetic
electrodes.Comment: RevTeX 10 pages, 4 figures, submitted to Phys.Rev. Let
Real-time gauge/gravity duality: Prescription, Renormalization and Examples
We present a comprehensive analysis of the prescription we recently put
forward for the computation of real-time correlation functions using
gauge/gravity duality. The prescription is valid for any holographic
supergravity background and it naturally maps initial and final data in the
bulk to initial and final states or density matrices in the field theory. We
show in detail how the technique of holographic renormalization can be applied
in this setting and we provide numerous illustrative examples, including the
computation of time-ordered, Wightman and retarded 2-point functions in
Poincare and global coordinates, thermal correlators and higher-point
functions.Comment: 85 pages, 13 figures; v2: added comments and reference
Current driven switching of magnetic layers
The switching of magnetic layers is studied under the action of a spin
current in a ferromagnetic metal/non-magnetic metal/ferromagnetic metal spin
valve. We find that the main contribution to the switching comes from the
non-equilibrium exchange interaction between the ferromagnetic layers. This
interaction defines the magnetic configuration of the layers with minimum
energy and establishes the threshold for a critical switching current.
Depending on the direction of the critical current, the interaction changes
sign and a given magnetic configuration becomes unstable. To model the time
dependence of the switching process, we derive a set of coupled Landau-Lifshitz
equations for the ferromagnetic layers. Higher order terms in the
non-equilibrium exchange coupling allow the system to evolve to its
steady-state configuration.Comment: 8 pages, 2 figure. Submitted to Phys. Rev.
Voltage-probe-controlled breakdown of the quantum Hall effect
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
Probe Branes, Time-dependent Couplings and Thermalization in AdS/CFT
We present holographic descriptions of thermalization in conformal field
theories using probe D-branes in AdS X S space-times. We find that the induced
metrics on Dp-brane worldvolumes which are rotating in an internal sphere
direction have horizons with characteristic Hawking temperatures even if there
is no black hole in the bulk AdS. The AdS/CFT correspondence applied to such
systems indeed reveals thermal properties such as Brownian motions and AC
conductivities in the dual conformal field theories. We also use this framework
to holographically analyze time-dependent systems undergoing a quantum quench,
where parameters in quantum field theories, such as a mass or a coupling
constant, are suddenly changed. We confirm that this leads to thermal behavior
by demonstrating the formation of apparent horizons in the induced metric after
a certain time.Comment: LaTeX, 47 pages, 14 figures; Typos corrected and references added
(v2); minor corrections, references added(v3
- …