535 research outputs found
Fast and robust two- and three-qubit swapping gates on multi-atomic ensembles in quantum electrodynamic cavity
Creation of quantum computer is outstanding fundamental and practical
problem. The quantum computer could be used for execution of very complicated
tasks which are not solvable with the classical computers. The first prototype
of solid state quantum computer was created in 2009 with superconducting
qubits. However, it suffers from the decoherent processes and it is desirable
to find more practical encoding of qubits with long-lived coherence. It could
be single impurity or vacancy centers in solids, but their interaction with
electromagnetic radiation is rather weak. So, here, ensembles of atoms were
proposed for the qubit encoding by using the dipole blockade mechanism in order
to turn multilevel systems in two level ones. But dipole-dipole based blockade
introduces an additional decoherence that limits its practical significance.
Recently, the collective blockade mechanism has been proposed for the system of
three-level atoms by using the different frequency shifts for the Raman
transitions between the collective atomic states characterized by a different
number of the excited atoms. Here, we propose two qubit gate by using another
collective blockade mechanism in the system of two level atoms based on
exchange interaction via the virtual photons between the multi-atomic ensembles
in the resonator. Also we demonstrate the possibility of three qubit gate
(Controlled SWAP gate) using a suppression of the swap-process between two
multi-atomic ensembles due to dynamical shift of the atomic levels controlled
by the states of photon encoded qubit
Pressure dependence of upper critical fields in FeSe single crystals
We investigate the pressure dependence of the upper critical fields
({\mu}) for FeSe single crystals with pressure up to 2.57 GPa.
The superconducting (SC) properties show a disparate behavior across a critical
pressure where the pressure-induced antiferromagnetic phase coexists with
superconductivity. The magnetoresistance for and is very
different: for , magnetic field induces and enhances a hump in the
resistivity close to the for pressures higher than 1.2 GPa, while it is
absent for . Since the measured {\mu} for FeSe samples is
smaller than the orbital limited upper critical field ()
estimated by the Werthamer Helfand and Hohenberg (WHH) model, the Maki
parameter ({\alpha}) related to Pauli spin-paramagnetic effects is additionally
considered to describe the temperature dependence of {\mu}().
Interestingly, the {\alpha} value is hardly affected by pressure for ,
while it strongly increases with pressure for . The pressure evolution of
the {\mu}(0)s for the FeSe single crystals is found to be almost
similar to that of (), suggesting that the pressure-induced magnetic
order adversely affects the upper critical fields as well as the SC transition
temperature.Comment: 23 pages, 6 figures, 1 tabl
Impact of climate change on the ground thermal regime in the lower Lena region, Arctic central Siberia
This paper presents the results of 30 years of permafrost thermal monitoring in the Tiksi area in the eastern Russian Arctic. At a stone ridge site, the mean annual temperatures in the upper 30 m of the ground have increased by 1–2.4 C compared to the first years of observations, with trends of C/yr. At the same time, its change was uneven. In the last 20 years, the rate of increase has increased compared with the first decade of observations. At wet tundra sites in the foothill plain, the mean annual temperatures at the top of permafrost have increased by 2.4–2.6 C between 2005 and 2022 at rates of 0.11–0.15 C/yr, and the active layer thicknesses have increased at rates of 0.05–0.41 cm/yr
Enhanced critical current density in the pressure-induced magnetic state of the high-temperature superconductor FeSe
We investigate the relation of the critical current density (Jc) and the
remarkably increased superconducting transition temperature (Tc) for the FeSe
single crystals under pressures up to 2.43 GPa, where the Tc is increased by ~8
K/GPa. The critical current density corresponding to the free flux flow is
monotonically enhanced by pressure which is due to the increase in Tc, whereas
the depinning critical current density at which the vortex starts to move is
more influenced by the pressure-induced magnetic state compared to the increase
of Tc. Unlike other high-Tc superconductors, FeSe is not magnetic, but
superconducting at ambient pressure. Above a critical pressure where magnetic
state is induced and coexists with superconductivity, the depinning Jc abruptly
increases even though the increase of the zero-resistivity Tc is negligible,
directly indicating that the flux pinning property compared to the Tc
enhancement is a more crucial factor for an achievement of a large Jc. In
addition, the sharp increase in Jc in the coexisting superconducting phase of
FeSe demonstrates that vortices can be effectively trapped by the competing
antiferromagnetic order, even though its antagonistic nature against
superconductivity is well documented. These results provide new guidance toward
technological applications of high-temperature superconductors.Comment: 24pages, 8 figure
Submarine permafrost map in the arctic modeled using 1-D transient heat flux (SuPerMAP)
Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 124(6), (2019): 3490-3507, doi:10.1029/2018JC014675.Offshore permafrost plays a role in the global climate system, but observations of permafrost thickness, state, and composition are limited to specific regions. The current global permafrost map shows potential offshore permafrost distribution based on bathymetry and global sea level rise. As a first‐order estimate, we employ a heat transfer model to calculate the subsurface temperature field. Our model uses dynamic upper boundary conditions that synthesize Earth System Model air temperature, ice mass distribution and thickness, and global sea level reconstruction and applies globally distributed geothermal heat flux as a lower boundary condition. Sea level reconstruction accounts for differences between marine and terrestrial sedimentation history. Sediment composition and pore water salinity are integrated in the model. Model runs for 450 ka for cross‐shelf transects were used to initialize the model for circumarctic modeling for the past 50 ka. Preindustrial submarine permafrost (i.e., cryotic sediment), modeled at 12.5‐km spatial resolution, lies beneath almost 2.5 ×106km2 of the Arctic shelf. Our simple modeling approach results in estimates of distribution of cryotic sediment that are similar to the current global map and recent seismically delineated permafrost distributions for the Beaufort and Kara seas, suggesting that sea level is a first‐order determinant for submarine permafrost distribution. Ice content and sediment thermal conductivity are also important for determining rates of permafrost thickness change. The model provides a consistent circumarctic approach to map submarine permafrost and to estimate the dynamics of permafrost in the past.Boundary condition data are available online via the sources referenced in the manuscript. This work was partially funded by a Helmholtz Association of Research Centres (HGF) Joint Russian‐German Research Group (HGF JRG 100). This study is part of a project that has received funding from the European Unions Horizon 2020 research and innovation program under grant agreement 773421. Submarine permafrost studies in the Kara and Laptev Seas were supported by Russian Foundation for Basic Research (RFBR/RFFI) grants 18‐05‐60004 and 18‐05‐70091, respectively. The International Permafrost Association (IPA) and the Association for Polar Early Career Scientists (APECS) supported research coordination that led to this study. We acknowledge coordination support of the World Climate Research Programme (WCRP) through their core project on Climate and Cryosphere (CliC). Thanks to Martin Jakobsson for providing a digitized version of the preliminary IHO delineation of the Arctic seas and to Guy Masters for access to the observational geothermal database. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.2019-10-1
- …