225 research outputs found
Long-range coupling and scalable architecture for superconducting flux qubits
Constructing a fault-tolerant quantum computer is a daunting task. Given any
design, it is possible to determine the maximum error rate of each type of
component that can be tolerated while still permitting arbitrarily large-scale
quantum computation. It is an underappreciated fact that including an
appropriately designed mechanism enabling long-range qubit coupling or
transport substantially increases the maximum tolerable error rates of all
components. With this thought in mind, we take the superconducting flux qubit
coupling mechanism described in PRB 70, 140501 (2004) and extend it to allow
approximately 500 MHz coupling of square flux qubits, 50 um a side, at a
distance of up to several mm. This mechanism is then used as the basis of two
scalable architectures for flux qubits taking into account crosstalk and
fault-tolerant considerations such as permitting a universal set of logical
gates, parallelism, measurement and initialization, and data mobility.Comment: 8 pages, 11 figure
Thermodynamics and Topology of Disordered Systems: Statistics of the Random Knot Diagrams on Finite Lattice
The statistical properties of random lattice knots, the topology of which is
determined by the algebraic topological Jones-Kauffman invariants was studied
by analytical and numerical methods. The Kauffman polynomial invariant of a
random knot diagram was represented by a partition function of the Potts model
with a random configuration of ferro- and antiferromagnetic bonds, which
allowed the probability distribution of the random dense knots on a flat square
lattice over topological classes to be studied. A topological class is
characterized by the highest power of the Kauffman polynomial invariant and
interpreted as the free energy of a q-component Potts spin system for
q->infinity. It is shown that the highest power of the Kauffman invariant is
correlated with the minimum energy of the corresponding Potts spin system. The
probability of the lattice knot distribution over topological classes was
studied by the method of transfer matrices, depending on the type of local
junctions and the size of the flat knot diagram. The obtained results are
compared to the probability distribution of the minimum energy of a Potts
system with random ferro- and antiferromagnetic bonds.Comment: 37 pages, latex-revtex (new version: misprints removed, references
added
Gauge vortex dynamics at finite mass of bosonic fields
The simple derivation of the string equation of motion adopted in the
nonrelativistic case is presented, paying the special attention to the effects
of finite masses of bosonic fields of an Abelian Higgs model. The role of the
finite mass effects in the evaluation of various topological characteristics of
the closed strings is discussed. The rate of the dissipationless helicity
change is calculated. It is demonstrated how the conservation of the sum of the
twisting and writhing numbers of the string is recovered despite the changing
helicity.Comment: considerably revised to include errata to journal versio
Influence of a knot on the strength of a polymer strand
Many experiments have been done to determine the relative strength of
different knots, and these show that the break in a knotted rope almost
invariably occurs at a point just outside the `entrance' to the knot. The
influence of knots on the properties of polymers has become of great interest,
in part because of their effect on mechanical properties. Knot theory applied
to the topology of macromolecules indicates that the simple trefoil or
`overhand' knot is likely to be present with high probability in any long
polymer strand. Fragments of DNA have been observed to contain such knots in
experiments and computer simulations. Here we use {\it ab initio} computational
methods to investigate the effect of a trefoil knot on the breaking strength of
a polymer strand. We find that the knot weakens the strand significantly, and
that, like a knotted rope, it breaks under tension at the entrance to the knot.Comment: 3 pages, 4 figure
On topological interpretation of quantum numbers
It is shown how one can define vector topological charges for topological
exitations of non-linear sigma-models on compact homogeneous spaces T_G and
G/T_G (where G is a simple compact Lie group and T_G is its maximal commutative
subgroup). Explicit solutions for some cases, their energies and interaction of
different topological charges are found. A possibility of the topological
interpretation of the quantum numbers of groups and particles is discussed.Comment: 20 pages, Latex 2e, modified versio
Heteropolymeric Triplex-Based Genomic Assay® to Detect Pathogens or Single-Nucleotide Polymorphisms in Human Genomic Samples
Human genomic samples are complex and are considered difficult to assay directly without denaturation or PCR amplification. We report the use of a base-specific heteropolymeric triplex, formed by native duplex genomic target and an oligonucleotide third strand probe, to assay for low copy pathogen genomes present in a sample also containing human genomic duplex DNA, or to assay human genomic duplex DNA for Single Nucleotide Polymorphisms (SNP), without PCR amplification. Wild-type and mutant probes are used to identify triplexes containing FVL G1691A, MTHFR C677T and CFTR mutations. The specific triplex structure forms rapidly at room temperature in solution and may be detected without a separation step. YOYO-1, a fluorescent bis-intercalator, promotes and signals the formation of the specific triplex. Genomic duplexes may be assayed homogeneously with single base pair resolution. The specific triple-stranded structures of the assay may approximate homologous recombination intermediates, which various models suggest may form in either the major or minor groove of the duplex. The bases of the stable duplex target are rendered specifically reactive to the bases of the probe because of the activity of intercalated YOYO-1, which is known to decondense duplex locally 1.3 fold. This may approximate the local decondensation effected by recombination proteins such as RecA in vivo. Our assay, while involving triplex formation, is sui generis, as it is not homopurine sequence-dependent, as are “canonical triplexes”. Rather, the base pair-specific heteropolymeric triplex of the assay is conformation-dependent. The highly sensitive diagnostic assay we present allows for the direct detection of base sequence in genomic duplex samples, including those containing human genomic duplex DNA, thereby bypassing the inherent problems and cost associated with conventional PCR based diagnostic assays
Force unfolding kinetics of RNA using optical tweezers. II. Modeling experiments
By exerting mechanical force it is possible to unfold/refold RNA molecules
one at a time. In a small range of forces, an RNA molecule can hop between the
folded and the unfolded state with force-dependent kinetic rates. Here, we
introduce a mesoscopic model to analyze the hopping kinetics of RNA hairpins in
an optical tweezers setup. The model includes different elements of the
experimental setup (beads, handles and RNA sequence) and limitations of the
instrument (time lag of the force-feedback mechanism and finite bandwidth of
data acquisition). We investigated the influence of the instrument on the
measured hopping rates. Results from the model are in good agreement with the
experiments reported in the companion article (1). The comparison between
theory and experiments allowed us to infer the values of the intrinsic
molecular rates of the RNA hairpin alone and to search for the optimal
experimental conditions to do the measurements. We conclude that long handles
and soft laser traps represent the best conditions to extract rate estimates
that are closest to the intrinsic molecular rates. The methodology and
rationale presented here can be applied to other experimental setups and other
molecules.Comment: PDF file, 32 pages including 9 figures plus supplementary materia
Numerical study of linear and circular model DNA chains confined in a slit: metric and topological properties
Advanced Monte Carlo simulations are used to study the effect of nano-slit
confinement on metric and topological properties of model DNA chains. We
consider both linear and circularised chains with contour lengths in the
1.2--4.8 m range and slits widths spanning continuously the 50--1250nm
range. The metric scaling predicted by de Gennes' blob model is shown to hold
for both linear and circularised DNA up to the strongest levels of confinement.
More notably, the topological properties of the circularised DNA molecules have
two major differences compared to three-dimensional confinement. First, the
overall knotting probability is non-monotonic for increasing confinement and
can be largely enhanced or suppressed compared to the bulk case by simply
varying the slit width. Secondly, the knot population consists of knots that
are far simpler than for three-dimensional confinement. The results suggest
that nano-slits could be used in nano-fluidic setups to produce DNA rings
having simple topologies (including the unknot) or to separate heterogeneous
ensembles of DNA rings by knot type.Comment: 12 pages, 10 figure
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