119 research outputs found
Theory of magnon motive force in chiral ferromagnets
We predict that magnon motive force can lead to temperature dependent,
nonlinear chiral damping in both conducting and insulating ferromagnets. We
estimate that this damping can significantly influence the motion of skyrmions
and domain walls at finite temperatures. We also find that in systems with low
Gilbert damping moving chiral magnetic textures and resulting magnon motive
forces can induce large spin and energy currents in the transverse direction
Parafermion stabilizer codes
We define and study parafermion stabilizer codes which can be viewed as
generalizations of Kitaev's one dimensional model of unpaired Majorana
fermions. Parafermion stabilizer codes can protect against low-weight errors
acting on a small subset of parafermion modes in analogy to qudit stabilizer
codes. Examples of several smallest parafermion stabilizer codes are given. A
locality preserving embedding of qudit operators into parafermion operators is
established which allows one to map known qudit stabilizer codes to parafermion
codes. We also present a local 2D parafermion construction that combines
topological protection of Kitaev's toric code with additional protection
relying on parity conservation
Stabilization and control of Majorana bound states with elongated skyrmions
We show that elongated magnetic skyrmions can host Majorana bound states in a
proximity-coupled two-dimensional electron gas sandwiched between a chiral
magnet and an -wave superconductor. Our proposal requires stable skyrmions
with unit topological charge, which can be realized in a wide range of
multilayer magnets, and allows quantum information transfer by using standard
methods in spintronics via skyrmion motion. We also show how braiding
operations can be realized in our proposal
Finite state verifiers with both private and public coins
We consider the effects of allowing a finite state verifier in an interactive
proof system to use a bounded number of private coins, in addition to "public"
coins whose outcomes are visible to the prover. Although swapping between
private and public-coin machines does not change the class of verifiable
languages when the verifiers are given reasonably large time and space bounds,
this distinction has well known effects for the capabilities of constant space
verifiers. We show that a constant private-coin "budget" (independent of the
length of the input) increases the power of public-coin interactive proofs with
finite state verifiers considerably, and provide a new characterization of the
complexity class as the set of languages that are verifiable by such
machines with arbitrarily small error in expected polynomial time.Comment: 18 pages, of which 5 pages are appendix, accepted for presentation in
the conference ICTCS 2023, and is to be published in its proceeding
Magnetic skyrmion bubble motion driven by surface acoustic waves
We study the dynamical control of a magnetic skyrmion bubble by using counter-propagating surface acoustic waves (SAWs) in a ferromagnet. First, we determine the bubble mass and derive the force due to SAWs acting on a magnetic bubble using Thiele\u27s method. The force that pushes the bubble is proportional to the strain gradient for the major strain component. We then study the dynamical pinning and motion of magnetic bubbles by SAWs in a nanowire. In a disk geometry, we propose a SAWs-driven skyrmion bubble oscillator with two resonant frequencies
PRISM: protein interactions by structural matching
Prism () is a website for protein interface analysis and prediction of putative protein–protein interactions. It is composed of a database holding protein interface structures derived from the Protein Data Bank (PDB). The server also includes summary information about related proteins and an interactive protein interface viewer. A list of putative protein–protein interactions obtained by running our prediction algorithm can also be accessed. These results are applied to a set of protein structures obtained from the PDB at the time of algorithm execution (January 2004). Users can browse through the non-redundant dataset of representative interfaces on which the prediction algorithm depends, retrieve the list of similar structures to these interfaces or see the results of interaction predictions for a particular protein. Another service provided is interactive prediction. This is done by running the algorithm for user input structures
Dynamical invariants for quantum control of four-level systems
We present a Lie-algebraic classification and detailed construction of the
dynamical invariants, also known as Lewis-Riesenfeld invariants, of the
four-level systems including two-qubit systems which are most relevant and
sufficiently general for quantum control and computation. These invariants not
only solve the time-dependent Schr\"odinger equation of four-level systems
exactly but also enable the control, and hence quantum computation based on
which, of four-level systems fast and beyond adiabatic regimes.Comment: 11 pages, 5 table
Minimal and Robust Composite Two-Qubit Gates with Ising-Type Interaction
We construct a minimal robust controlled-NOT gate with an Ising-type
interaction by which elementary two-qubit gates are implemented. It is robust
against inaccuracy of the coupling strength and the obtained quantum circuits
are constructed with the minimal number (N=3) of elementary two-qubit gates and
several one-qubit gates. It is noteworthy that all the robust circuits can be
mapped to one-qubit circuits robust against a pulse length error. We also prove
that a minimal robust SWAP gate cannot be constructed with N=3, but requires
N=6 elementary two-qubit gates.Comment: 7 pages, 2 figure
Stability of skyrmion lattices and symmetries of quasi-two-dimensional chiral magnets
Recently there has been substantial interest in realizations of skyrmions, in particular in quasi-two-dimensional (2D) systems due to increased stability resulting from reduced dimensionality. A stable skyrmion, representing the smallest realizable magnetic texture, could be an ideal element for ultradense magnetic memories. Here we use the most general form of the quasi-2D free energy with Dzyaloshinskii-Moriya interactions constructed from general symmetry considerations reflecting the underlying system. We predict that the skyrmion phase is robust and it is present even when the system lacks the in-plane rotational symmetry. In fact, the lowered symmetry leads to increased stability of vortex-antivortex lattices with fourfold symmetry and in-plane spirals, in some instances even in the absence of an external magnetic field. Our results relate different hexagonal and square cell phases to the symmetries of materials used for realizations of skyrmions. This will give clear directions for experimental realizations of hexagonal and square cell phases, and will allow engineering of skyrmions with unusual properties. We also predict striking differences in gyrodynamics induced by spin currents for isolated skyrmions and for crystals where spin currents can be induced by charge carriers or by thermal magnons. We find that under certain conditions, isolated skyrmions can move along the current without a side motion which can have implications for realizations of magnetic memories
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