308 research outputs found
Magic state distillation in all prime dimensions using quantum Reed-Muller codes
We propose families of protocols for magic state distillation -- important
components of fault tolerance schemes --- for systems of odd prime dimension.
Our protocols utilize quantum Reed-Muller codes with transversal non-Clifford
gates. We find that, in higher dimensions, small and effective codes can be
used that have no direct analogue in qubit (two-dimensional) systems. We
present several concrete protocols, including schemes for three-dimensional
(qutrit) and five-dimensional (ququint) systems. The five-dimensional protocol
is, by many measures, the best magic state distillation scheme yet discovered.
It excels both in terms of error threshold with respect to depolarising noise
(36.3%) and the efficiency measure know as "yield", where, for a large region
of parameters, it outperforms its qubit counterpart by many orders of
magnitude.Comment: Updated from V1 to include results on the remarkable d=5 cas
A Raman study of the Charge-Density-Wave State in AMoO (A = K,Rb)
We report a comparative Raman spectroscopic study of the
quasi-one-dimensional charge-density-wave systems \ab (A = K, Rb). The
temperature and polarization dependent experiments reveal charge-coupled
vibrational Raman features. The strongly temperature-dependent collective
amplitudon mode in both materials differ by about 3 cm, thus revealing the role
of alkali atom. We discus the observed vibrational features in terms of
charge-density-wave ground state accompanied by change in the crystal symmetry.
A frequency-kink in some modes seen in \bb between T = 80 K and 100 K supports
the first-order lock-in transition, unlike \rb. The unusually sharp Raman
lines(limited by the instrumental response) at very low temperatures and their
temperature evolution suggests that the decay of the low energy phonons is
strongly influenced by the presence of the temperature dependent charge density
wave gap.Comment: 13 pages, 7 figure
Entanglement-assisted quantum low-density parity-check codes
This paper develops a general method for constructing entanglement-assisted
quantum low-density parity-check (LDPC) codes, which is based on combinatorial
design theory. Explicit constructions are given for entanglement-assisted
quantum error-correcting codes (EAQECCs) with many desirable properties. These
properties include the requirement of only one initial entanglement bit, high
error correction performance, high rates, and low decoding complexity. The
proposed method produces infinitely many new codes with a wide variety of
parameters and entanglement requirements. Our framework encompasses various
codes including the previously known entanglement-assisted quantum LDPC codes
having the best error correction performance and many new codes with better
block error rates in simulations over the depolarizing channel. We also
determine important parameters of several well-known classes of quantum and
classical LDPC codes for previously unsettled cases.Comment: 20 pages, 5 figures. Final version appearing in Physical Review
Analytical Bethe Ansatz for closed and open gl(n)-spin chains in any representation
We present an "algebraic treatment" of the analytical Bethe Ansatz. For this
purpose, we introduce abstract monodromy and transfer matrices which provide an
algebraic framework for the analytical Bethe Ansatz. It allows us to deal with
a generic gl(n)-spin chain possessing on each site an arbitrary
gl(n)-representation. For open spin chains, we use the classification of the
reflection matrices to treat all the diagonal boundary cases. As a result, we
obtain the Bethe equations in their full generality for closed and open spin
chains. The classifications of finite dimensional irreducible representations
for the Yangian (closed spin chains) and for the reflection algebras (open spin
chains) are directly linked to the calculation of the transfer matrix
eigenvalues. As examples, we recover the usual closed and open spin chains, we
treat the alternating spin chains and the closed spin chain with impurity
On the verge of Umdeutung in Minnesota: Van Vleck and the correspondence principle (Part One)
In October 1924, the Physical Review, a relatively minor journal at the time,
published a remarkable two-part paper by John H. Van Vleck, working in virtual
isolation at the University of Minnesota. Van Vleck combined advanced
techniques of classical mechanics with Bohr's correspondence principle and
Einstein's quantum theory of radiation to find quantum analogues of classical
expressions for the emission, absorption, and dispersion of radiation. For
modern readers Van Vleck's paper is much easier to follow than the famous paper
by Kramers and Heisenberg on dispersion theory, which covers similar terrain
and is widely credited to have led directly to Heisenberg's "Umdeutung" paper.
This makes Van Vleck's paper extremely valuable for the reconstruction of the
genesis of matrix mechanics. It also makes it tempting to ask why Van Vleck did
not take the next step and develop matrix mechanics himself.Comment: 82 page
Stromal Vascular Fraction Transplantation as an Alternative Therapy for Ischemic Heart Failure: Anti-inflammatory Role
<p>Abstract</p> <p>Background</p> <p>The aims of this study were: (1) to show the feasibility of using adipose-derived stromal vascular fraction (SVF) as an alternative to bone marrow mono nuclear cell (BM-MNC) for cell transplantation into chronic ischemic myocardium; and (2) to explore underlying mechanisms with focus on anti-inflammation role of engrafted SVF and BM-MNC post chronic myocardial infarction (MI) against left ventricular (LV) remodelling and cardiac dysfunction.</p> <p>Methods</p> <p>Four weeks after left anterior descending coronary artery ligation, 32 Male Lewis rats with moderate MI were divided into 3 groups. SVF group (n = 12) had SVF cell transplantation (6 × 10<sup>6 </sup>cells). BM-MNC group (n = 12) received BM-MNCs (6 × 10<sup>6</sup>) and the control (n = 10) had culture medium. At 4 weeks, after the final echocardiography, histological sections were stained with Styrus red and immunohistochemical staining was performed for α-smooth muscle actin, von Willebrand factor, CD3, CD8 and CD20.</p> <p>Results</p> <p>At 4 weeks, in SVF and BM-MNC groups, LV diastolic dimension and LV systolic dimension were smaller and fractional shortening was increased in echocardiography, compared to control group. Histology revealed highest vascular density, CD3+ and CD20+ cells in SVF transplanted group. SVF transplantation decreased myocardial mRNA expression of inflammatory cytokines TNF-α, IL-6, MMP-1, TIMP-1 and inhibited collagen deposition.</p> <p>Conclusions</p> <p>Transplantation of adipose derived SVF cells might be a useful therapeutic option for angiogenesis in chronic ischemic heart disease. Anti-inflammation role for SVF and BM transplantation might partly benefit for the cardioprotective effect for chronic ischemic myocardium.</p
Combined intermittent hypoxia and surface muscle electrostimulation as a method to increase peripheral blood progenitor cell concentration
Background: Our goal was to determine whether short-term intermittent hypoxia exposure, at a level well tolerated by healthy humans and previously shown by our group to increase EPO and erythropoiesis, could mobilizehematopoietic stem cells (HSC) and increase their presence in peripheral circulation. Methods: Four healthy male subjects were subjected to three different protocols: one with only a hypoxic stimulus (OH), another with a hypoxic stimulus plus muscle electrostimulation (HME) and the third with only muscle electrostimulation (OME). Intermittent hypobaric hypoxia exposureconsisted of only three sessions of three hours at barometric pressure 540 hPa (equivalent to an altitude of 5000 m) for three consecutive days, whereas muscular electrostimulation was performed in two separate periods of 25 min in each session. Blood samples were obtained from an antecubital vein on three consecutive days immediately before the experiment and 24 h, 48 h, 4 days and 7 days after the last day of hypoxic exposure. Results: There was a clear increase in the number of circulating CD34+ cells after combined hypobaric hypoxia and muscular electrostimulation. This response was not observed after the isolated application of the same stimuli. Conclusion: Our results open a new application field for hypobaric systems as a way to increase efficiency in peripheral HSC collection
Endothelial progenitor cells and integrins: adhesive needs
In the last decade there have been multiple studies concerning the contribution of endothelial progenitor cells (EPCs) to new vessel formation in different physiological and pathological settings. The process by which EPCs contribute to new vessel formation in adults is termed postnatal vasculogenesis and occurs via four inter-related steps. They must respond to chemoattractant signals and mobilize from the bone marrow to the peripheral blood; home in on sites of new vessel formation; invade and migrate at the same sites; and differentiate into mature endothelial cells (ECs) and/or regulate pre-existing ECs via paracrine or juxtacrine signals. During these four steps, EPCs interact with different physiological compartments, namely bone marrow, peripheral blood, blood vessels and homing tissues. The success of each step depends on the ability of EPCs to interact, adapt and respond to multiple molecular cues. The present review summarizes the interactions between integrins expressed by EPCs and their ligands: extracellular matrix components and cell surface proteins present at sites of postnatal vasculogenesis. The data summarized here indicate that integrins represent a major molecular determinant of EPC function, with different integrin subunits regulating different steps of EPC biology. Specifically, integrin α4β1 is a key regulator of EPC retention and/or mobilization from the bone marrow, while integrins α5β1, α6β1, αvβ3 and αvβ5 are major determinants of EPC homing, invasion, differentiation and paracrine factor production. β2 integrins are the major regulators of EPC transendothelial migration. The relevance of integrins in EPC biology is also demonstrated by many studies that use extracellular matrix-based scaffolds as a clinical tool to improve the vasculogenic functions of EPCs. We propose that targeted and tissue-specific manipulation of EPC integrin-mediated interactions may be crucial to further improve the usage of this cell population as a relevant clinical agent
Magnetotransport of CeRhIn5
We report measurements of the temperature-dependent anisotropic resistivity
and in-plane magnetoresistance on single crystals of the tetragonal
heavy-fermion antiferromagnet (TN = 3.8 K) CeRhIn5. The measurements are
reported in the temperature range 1.4 K to 300 K and in magnetic fields to 18
tesla. The resistivity is moderately anisotropic, with a room-temperature
c-axis to in-plane resistivity ratio rho_c/rho_a(300 K) = 1.7. rho(T)
measurements on the non-magnetic analog LaRhIn5 indicate that the anisotropy in
the CeRhIn5 resistivity stems predominately from anisotropy in Kondo-derived
magnetic scattering. In the magnetically ordered regime an applied field H
reduces TN only slightly due to the small ordered moment (0.37mu_B) and
magnetic anisotropy. The magnetoresistance (MR) below TN is positive and varies
linearly with H. In the paramagnetic state a positive MR is present below 7.5
K, while a high-field negative contribution is evident at higher temperatures.
The positive contribution decreases in magnitude with increasing temperature.
Above 40 K the positive contribution is no longer observable, and the MR is
negative. The low-T positive MR results from interactions with the
Kondo-coherent state, while the high-T negative MR stems from single-impurity
effects. The H and T-dependent magnetotransport reflects the magnetic
anisotropy and Kondo interactions at play in CeRhIn5.Comment: submitted to Physical Review
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