Spin Chains as Perfect Quantum State Mirrors

Quantum information transfer is an important part of quantum information processing. Several proposals for quantum information transfer along linear arrays of nearest-neighbor coupled qubits or spins were made recently. Perfect transfer was shown to exist in two models with specifically designed strongly inhomogeneous couplings. We show that perfect transfer occurs in an entire class of chains, including systems whose nearest-neighbor couplings vary only weakly along the chain. The key to these observations is the Jordan-Wigner mapping of spins to noninteracting lattice fermions which display perfectly periodic dynamics if the single-particle energy spectrum is appropriate. After a half-period of that dynamics any state is transformed into its mirror image with respect to the center of the chain. The absence of fermion interactions preserves these features at arbitrary temperature and allows for the transfer of nontrivially entangled states of several spins or qubits.Comment: Abstract extended, introduction shortened, some clarifications in the text, one new reference. Accepted by Phys. Rev. A (Rapid Communications

Zero--Temperature Quantum Phase Transition of a Two--Dimensional Ising Spin--Glass

We study the quantum transition at $T=0$ in the spin-$\frac12$ Ising spin--glass in a transverse field in two dimensions. The world line path integral representation of this model corresponds to an effective classical system in (2+1) dimensions, which we study by Monte Carlo simulations. Values of the critical exponents are estimated by a finite-size scaling analysis. We find that the dynamical exponent, $z$, and the correlation length exponent, $\nu$, are given by $z = 1.5 \pm 0.05$ and $\nu = 1.0 \pm 0.1$. Both the linear and non-linear susceptibility are found to diverge at the critical point.Comment: RevTeX 10 pages + 4 figures (appended as uuencoded, compressed tar-file), THP21-9

Factors Relating to Gender Specificity of Unloading-Induced Declines in Strength

Introduction: This investigation aimed to: (1) confirm whether women were more vulnerable to the negative neuromuscular adaptations elicited by muscle unloading and if so, (2) determine which physiological mechanism(s) explain those gender-related differences. Methods: Healthy young men (20.7 +/- 0.3 years) and women (20.3 +/- 0.3 years)-(N = 12/group)-participated by completing neuromuscular functional tests before and after 7 days of unloading. Results: During isokinetic testing of peak torque, work performed, and power, women displayed significantly (P \u3c = 0.05) greater declines in performance than men at 1.05 and 2.09, but not 0.53 rads/s. During maximal isometric contractions, women experienced greater strength decrements. Similar gender-specific adaptations to unloading were found in EMG activity, but not muscle mass, neuromuscular transmission, or force relative to EMG. Conclusions: Women are more susceptible to the adaptations of muscle unloading, and disturbances in neural drive from the central nervous system are probably responsible. Muscle Nerve 46: 210-217, 201

Five-Year Growth of Rock Lichens in a Low-Arctic Mountain Environment, Northern Labrador

In 1978, three lichen growth stations were established for Rhizocarpon section Rhizocarpon species and one for Alectoria miniscula in the Cirque Mountain area of the Torngat mountains. Five years later, in 1983, the lichens were remeasured. The five-year growth represented by the change in the theoretical diameter is very variable, between 0.10 and 0.54 mm per year. These rates are larger than expected and exceed rates previously determined for an eastern Arctic area, the Northern Cumberland Peninsula of Baffin Island, by more than 3 to more than 20 times. Similar rates are known for 'great period' growth outside Arctic regions. If the growth rates represent long-term growth, the ages of recessional moraines in the Torngat Mountains should be recalculated. Moraines formerly described as Late Wisconsin to mid-Holocene may be of Neoglacial age. Variability of growth rates from one individual to another precludes using these data for constructing growth curves which may be used, even locally, in lichenometric dating.En 1978, on a établi quatre sites de croissance du lichen dans la région du mont du Cirque dans les monts Torngat: trois sites des espèces Rhizocarpon de la section Rhizocarpon et un site de Alectoria miniscula. Cinq ans plus tard, en 1983, on a mesuré de nouveau les lichens pour constater que le diamètre moyen, qui témoigne de la croissance, a crû de manière très variable, soit de 0,10 à 0,54 mm par année. Ces taux de croissance sont plus élevés que prévu puisqu'ils dépassent de 3 à 20 fois les taux déjà mesurés dans le nord de la péninsule de Cumberland, île de Baffin. De tels taux de croissance du lichen s'apparentent davantage à ceux que l'on a observé dans les régions non arctiques au cours de sa période dite de grande croissance. Si ces taux s'appliquent à de longues périodes, il faudrait réévaluer la date de dépôt des moraines de récession dans les monts Torngat. Les moraines, que l'on croit dater de la période s'étendant du Wisconsinien supérieur à l'Holocène moyen, pourraient en fait dater du néoglaciaire. Toutefois, les variations observées entre les taux de croissance ne permettent pas d'utiliser ces données, même à l'échelle locale, pour tracer des courbes de croissance qui serviraient à établir des datations lichénométriques.1978 wurden im Cirque-Mountain-Gebiet der Torngat mountains vier Stationen zur Beobachtung des Flechten-Wachstums eingerichtet : drei Stationen fur Rhizocarpon-Arten der Sektion Rhizocarpon und eine Station fur Alectoria miniscula. Fùnf Jahre spâter, 1983, wurden die Flechten wieder gemessen. Der Fùnfjahreswuchs, der sich im Wechsel des durchschnittlichen Durchmessers ablesen IaBt, ist sehr unterschiedlich, zwischen 0.10 und 0.54 mm pro Jahr. Dièse Wachstumsraten sind grôfîer als erwartet und gehen ùber die zuvor fur ein ôstliches arktisches Gebiet, die Nord-Cumberland HaIbinsel der lnsel Baffin, bestimmten Raten mehr als dreifach bis zu mehr als zwanzigfach hinaus. Àhnliche Wachstumsraten sind fur die "groBe Periode" des Flechten-Wachstums auBerhalb der arktischen Gebiete bekannt. Wenn die Wachstumsraten Langzeit-Wachstum reprâsentieren, mûfite das Alter der Rùckzugs-Morànen in den Torngat-Bergen neu berechnet werden. Morànen, die zuvor dem spàten Wisconsin bis mittleren Holozân zugeschrieben wurden, kônnten aus der Neoglazialzeit stammen. Die Variationen der Wachstumsraten von einer Person zur anderen schlieBen eine Nutzung dieser Daten zum Aufbau von Wachstumskurven aus, welche, selbst lokal, zur Datierung auf der Basis der Flechten benutzt werden kônnten

Spectral, mineralogical, and geochemical variations across Home Plate, Gusev Crater, Mars indicate high and low temperature alteration

Over the last ~ 3 years in Gusev Crater, Mars, the Spirit rover observed coherent variations in color, mineralogy, and geochemistry across Home Plate, an ~ 80 m-diameter outcrop of basaltic tephra. Observations of Home Plate from orbit and from the summit of Husband Hill reveal clear differences in visible/near-infrared (VNIR) colors between its eastern and western regions that are consistent with mineralogical compositions indicated by Mössbauer spectrometer (MB) and by Miniature Thermal Emission Spectrometer (Mini-TES). Pyroxene and magnetite dominate the east side, while olivine, nanophase Fe oxide (npOx) and glass are more abundant on the western side. Alpha Particle X-Ray Spectrometer (APXS) observations reveal that eastern Home Plate has higher Si/Mg, Al, Zn, Ni, and K, while Cl and Br are higher in the west. We propose that these variations are the result of two distinct alteration regimes that may or may not be temporally related: a localized, higher temperature recrystallization and alteration of the east side of Home Plate and lower temperature alteration of the western side that produced npOx

Possible Ni-Rich Mafic-Ultramafic Magmatic Sequence in the Columbia Hills: Evidence from the Spirit Rover

The Spirit rover landed on geologic units of Hesperian age in Gusev Crater. The Columbia Hills rise above the surrounding plains materials, but orbital images show that the Columbia Hills are older [1, 2]. Spirit has recently descended the southeast slope of the Columbia Hills doing detailed measurements of a series of outcrops. The mineralogical and compositional data on these rocks are consistent with an interpretation as a magmatic sequence becoming increasingly olivine-rich down slope. The outcrop sequence is Larry s Bench, Seminole, Algonquin and Comanche. The "teeth" on the Rock Abrasion Tool (RAT) wore away prior to arrival at Larry s Bench; the data discussed are for RAT brushed surfaces

Griffiths-McCoy singularities in random quantum spin chains: Exact results through renormalization

The Ma-Dasgupta-Hu renormalization group (RG) scheme is used to study singular quantities in the Griffiths phase of random quantum spin chains. For the random transverse-field Ising spin chain we have extended Fisher's analytical solution to the off-critical region and calculated the dynamical exponent exactly. Concerning other random chains we argue by scaling considerations that the RG method generally becomes asymptotically exact for large times, both at the critical point and in the whole Griffiths phase. This statement is checked via numerical calculations on the random Heisenberg and quantum Potts models by the density matrix renormalization group method.Comment: 4 pages RevTeX, 2 figures include