2,272 research outputs found
Efficient current-induced domain-wall displacement SrRuO3
We demonstrate current-induced displacement of ferromagnetic domain walls in
sub-micrometer fabricated patterns of SrRuO3 films. The displacement, monitored
by measuring the extraordinary Hall effect, is induced at zero applied magnetic
field and its direction is reversed when the current is reversed. We find that
current density in the range of 10^9 - 10^10 A/m^2 is sufficient for
domain-wall displacement when the depinning field varies between 50 to 500 Oe.
These results indicate relatively high efficiency of the current in displacing
domain walls which we believe is related to the narrow width ~3 nm of domain
walls in this compound
Finding the ground state of the Hubbard model by variational methods on a quantum computer with gate errors
A key goal of digital quantum computing is the simulation of fermionic
systems such as molecules or the Hubbard model. Unfortunately, for present and
near-future quantum computers the use of quantum error correction schemes is
still out of reach. Hence, the finite error rate limits the use of quantum
computers to algorithms with a low number of gates. The variational Hamiltonian
ansatz (VHA) has been shown to produce the ground state in good approximation
in a manageable number of steps. Here we study explicitly the effect of gate
errors on its performance. The VHA is inspired by the adiabatic quantum
evolution under the influence of a time-dependent Hamiltonian, where the -
ideally short - fixed Trotter time steps are replaced by variational
parameters. The method profits substantially from quantum variational error
suppression, e.g., unitary quasi-static errors are mitigated within the
algorithm. We test the performance of the VHA when applied to the Hubbard model
in the presence of unitary control errors on quantum computers with realistic
gate fidelities.Comment: 5+1 pages, 2 figures, 3 table
Emulating the one-dimensional Fermi-Hubbard model by a double chain of qubits
The Jordan-Wigner transformation maps a one-dimensional (1D) spin-
1
/
2
system onto a fermionic model without spin degree of freedom. A double chain of quantum bits with
X
X
and
Z
Z
couplings of neighboring qubits along and between the chains, respectively, can be mapped on a spin-full 1D Fermi-Hubbard model. The qubit system can thus be used to emulate the quantum properties of this model. We analyze physical implementations of such analog quantum simulators, including one based on transmon qubits, where the
Z
Z
interaction arises due to an inductive coupling and the
X
X
interaction due to a capacitive interaction. We propose protocols to gain confidence in the results of the simulation through measurements of local operators
A Kinetic Model for Grain Growth
We provide a well-posedness analysis of a kinetic model for grain growth
introduced by Fradkov which is based on the von Neumann-Mullins law. The model
consists of an infinite number of transport equations with a tri-diagonal
coupling modelling topological changes in the grain configuration.
Self-consistency of this kinetic model is achieved by introducing a coupling
weight which leads to a nonlinear and nonlocal system of equations.
We prove existence of solutions by approximation with finite dimensional
systems. Key ingredients in passing to the limit are suitable super-solutions,
a bound from below on the total mass, and a tightness estimate which ensures
that no mass is transported to infinity in finite time.Comment: 24 page
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