12,905 research outputs found
Higher harmonics of azimuthal anisotropy in relativistic heavy ion collisions in HYDJET++ model
The LHC data on azimuthal anisotropy harmonics from PbPb collisions at
center-of-mass energy 2.76 TeV per nucleon pair are analyzed and interpreted in
the framework of the HYDJET++ model. The cross-talk of elliptic and
triangular flow in the model generates both even and odd harmonics of
higher order. Comparison with the experimental data shows that this mechanism
is able to reproduce the and centrality dependencies of
quadrangular flow , and also the basic trends for pentagonal and
hexagonal flows.Comment: 12 pages including 13 figures as EPS-files; prepared using LaTeX
package for publication in the European Physical Journal
Effects of quasiparticle tunneling in a circuit-QED realization of a strongly driven two-level system
We experimentally and theoretically study the frequency shift of a driven
cavity coupled to a superconducting charge qubit. In addition to previous
studies, we here also consider drive strengths large enough to energetically
allow for quasiparticle creation. Quasiparticle tunneling leads to the
inclusion of more than two charge states in the dynamics. To explain the
observed effects, we develop a master equation for the microwave dressed charge
states, including quasiparticle tunneling. A bimodal behavior of the frequency
shift as a function of gate voltage can be used for sensitive charge detection.
However, at weak drives the charge sensitivity is significantly reduced by
non-equilibrium quasiparticles, which induce transitions to a non-sensitive
state. Unexpectedly, at high enough drives, quasiparticle tunneling enables a
very fast relaxation channel to the sensitive state. In this regime, the charge
sensitivity is thus robust against externally injected quasiparticles and the
desired dynamics prevail over a broad range of temperatures. We find very good
agreement between theory and experiment over a wide range of drive strengths
and temperatures.Comment: 25 pages, 7 figure
Dynamic parity recovery in a strongly driven Cooper-pair box
We study a superconducting charge qubit coupled to an intensive
electromagnetic field and probe changes in the resonance frequency of the
formed dressed states. At large driving strengths, exceeding the qubit
energy-level splitting, this reveals the well known Landau-Zener-Stuckelberg
(LZS) interference structure of a longitudinally driven two-level system. For
even stronger drives we observe a significant change in the LZS pattern and
contrast. We attribute this to photon-assisted quasiparticle tunneling in the
qubit. This results in the recovery of the qubit parity, eliminating effects of
quasiparticle poisoning and leads to an enhanced interferometric response. The
interference pattern becomes robust to quasiparticle poisoning and has a good
potential for accurate charge sensing.Comment: 5 pages, 4 figure
The peculiar extinction law of SN2014J measured with The Hubble Space Telescope
The wavelength-dependence of the extinction of Type Ia SN2014J in the nearby
galaxy M82 has been measured using UV to near-IR photometry obtained with the
Hubble Space Telescope, the Nordic Optical Telescope, and the Mount Abu
Infrared Telescope. This is the first time that the reddening of a SN Ia is
characterized over the full wavelength range of - microns. A
total-to-selective extinction, , is ruled out with high
significance. The best fit at maximum using a Galactic type extinction law
yields . The observed reddening of SN2014J is also compatible
with a power-law extinction, as expected from multiple scattering of light, with
. After correction for differences in reddening, SN2014J appears
to be very similar to SN2011fe over the 14 broad-band filter light curves used
in our study.Comment: Accepted for publication in ApJ
Observation of the Dynamical Casimir Effect in a Superconducting Circuit
One of the most surprising predictions of modern quantum theory is that the
vacuum of space is not empty. In fact, quantum theory predicts that it teems
with virtual particles flitting in and out of existence. While initially a
curiosity, it was quickly realized that these vacuum fluctuations had
measurable consequences, for instance producing the Lamb shift of atomic
spectra and modifying the magnetic moment for the electron. This type of
renormalization due to vacuum fluctuations is now central to our understanding
of nature. However, these effects provide indirect evidence for the existence
of vacuum fluctuations. From early on, it was discussed if it might instead be
possible to more directly observe the virtual particles that compose the
quantum vacuum. 40 years ago, Moore suggested that a mirror undergoing
relativistic motion could convert virtual photons into directly observable real
photons. This effect was later named the dynamical Casimir effect (DCE). Using
a superconducting circuit, we have observed the DCE for the first time. The
circuit consists of a coplanar transmission line with an electrical length that
can be changed at a few percent of the speed of light. The length is changed by
modulating the inductance of a superconducting quantum interference device
(SQUID) at high frequencies (~11 GHz). In addition to observing the creation of
real photons, we observe two-mode squeezing of the emitted radiation, which is
a signature of the quantum character of the generation process.Comment: 12 pages, 3 figure
Probing High Frequency Noise with Macroscopic Resonant Tunneling
We have developed a method for extracting the high-frequency noise spectral
density of an rf-SQUID flux qubit from macroscopic resonant tunneling (MRT)
rate measurements. The extracted noise spectral density is consistent with that
of an ohmic environment up to frequencies ~ 4 GHz. We have also derived an
expression for the MRT lineshape expected for a noise spectral density
consisting of such a broadband ohmic component and an additional strongly
peaked low-frequency component. This hybrid model provides an excellent fit to
experimental data across a range of tunneling amplitudes and temperatures
Discreteness-Induced Oscillatory Instabilities of Dark Solitons
We reveal that even weak inherent discreteness of a nonlinear model can lead
to instabilities of the localized modes it supports. We present the first
example of an oscillatory instability of dark solitons, and analyse how it may
occur for dark solitons of the discrete nonlinear Schrodinger and generalized
Ablowitz-Ladik equations.Comment: 11 pages, 4 figures, to be published in Physical Review Letter
Coherent current transport in wide ballistic Josephson junctions
We present an experimental and theoretical investigation of coherent current
transport in wide ballistic superconductor-two dimensional electron
gas-superconductor junctions. It is found experimentally that upon increasing
the junction length, the subharmonic gap structure in the current-voltage
characteristics is shifted to lower voltages, and the excess current at
voltages much larger than the superconducting gap decreases. Applying a theory
of coherent multiple Andreev reflection, we show that these observations can be
explained in terms of transport through Andreev resonances.Comment: 4 pages, 4 figure
On a conjecture of Widom
We prove a conjecture of H.Widom stated in [W] (math/0108008) about the
reality of eigenvalues of certain infinite matrices arising in asymptotic
analysis of large Toeplitz determinants. As a byproduct we obtain a new proof
of A.Okounkov's formula for the (determinantal) correlation functions of the
Schur measures on partitions.Comment: 9 page
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