93 research outputs found
Various Correlations in Anisotropic Heisenberg XYZ Model with Dzyaloshinski-Moriya Interaction
Various thermal correlations as well as the effect of intrinsic decoherence
on the correlations are studied in a two-qubit Heisenberg XYZ spin chain with
the Dzyaloshinski--Moriya (DM) interaction along the z direction, i.e. Dz. It
is found that tunable parameter Dz may play a constructive role on the
concurrence (C), classical correlation (CC) and quantum discord (QD) in thermal
equilibrium while it plays a destructive role on the correlations in the
intrinsic decoherence case. The entanglement and quantum discord exhibit
collapse and revival under the phase decoherence. With a proper combination of
the system parameters, the correlations can effectively be kept at high steady
state values despite the intrinsic decoherence.Comment: 4 pages, 4 figure
High Pressure Effects on Superconductivity in the beta-pyrochlore Oxides AOs2O6 (A=K, Rb, Cs)
Recently new pyrochlore oxides superconductors AOs2O6 (A=K,Rb,Cs) were found
and we measured the pressure dependence of magnetization up to 1.2 GPa in order
to deduce the pressure effect of Tc in the three beta-pyrochlore oxides. It is
found that the initial pressure dependence of Tc is positive for all the
compounds. Only KOs2O6 exhibits a saturation in Tc at 0.56 GPa and the downturn
at higher pressureComment: 7 pages, 2 figure
Electrical resistivity and tunneling anomalies in CeCuAs2
The compound CeCuAs2 is found to exhibit negative temperature (T) coefficient
of electrical resistivity (rho) under ambient pressure conditions in the entire
T-range of investigation (45 mK to 300 K), even in the presence of high
magnetic fields. Preliminary tunneling spectroscopic measurements indicate the
existence of a psuedo-gap at least at low temperatures, thereby implying that
this compound could be classified as a Kondo semi-conductor, though rho(T)
interestingly is not found to be of an activated type.Comment: To appear in the proceedings of SCES200
Biomechanical and functional variation in rat sciatic nerve following cuff electrode implantation
Nerve cuff electrodes are commonly and successfully used for stimulating peripheral nerves. On the other hand, they occasionally induce functional and morphological changes following chronic implantation, for reasons not always clear. We hypothesize that restriction of nerve mobility due to cuff implantation may alter nerve conduction. We quantified acute changes in nerve-muscle electrophysiology, using electromyography, and nerve kinematics in anesthetized Sprague Dawley rat sciatic nerves during controlled hindlimb joint movement. We compared electrophysiological and biomechanical response in uncuffed nerves and those secured within a cuff electrode using analysis of variance (ANOVA) and regression analysis. Tethering resulting from cuff implantation resulted in altered nerve strain and a complex biomechanical environment during joint movement. Coincident with biomechanical changes, electromyography revealed significantly increased variability in the response of conduction latency and amplitude in cuffed, but not free, nerves following joint movement. Our findings emphasize the importance of the mechanical interface between peripheral nerves and their devices on neurophysiological performance. This work has implications for nerve device design, implantation, and prediction of long-term efficacy.https://doi.org/10.1186/1743-0003-11-7
^{63,65}Cu NMR and NQR evidence for an unusual spin dynamics in PrCu_2 below 100 K
We report the results of a Cu NMR/NQR study probing the
intermetallic compound PrCu. The previously claimed onset of magnetic order
at 65 K, indicated in a SR study, is not confirmed. Based on our data we
discuss different possible reasons for this apparent discrepancy, including a
non negligible influence of the implanted muons on their environment. Competing
dipolar and quadrupolar interactions lead to unusual features of the
magnetic-ion/conduction-electron system, different from those of common
intermetallics exhibiting structural or magnetic instabilities.Comment: 8 pages, 7 figures, submitted to Phys Rev
State transfer in dissipative and dephasing environments
By diagonalization of a generalized superoperator for solving the master
equation, we investigated effects of dissipative and dephasing environments on
quantum state transfer, as well as entanglement distribution and creation in
spin networks. Our results revealed that under the condition of the same
decoherence rate , the detrimental effects of the dissipative
environment are more severe than that of the dephasing environment. Beside
this, the critical time at which the transfer fidelity and the
concurrence attain their maxima arrives at the asymptotic value
quickly as the spin chain length increases. The transfer
fidelity of an excitation at time is independent of when the system
subjects to dissipative environment, while it decreases as increases when
the system subjects to dephasing environment. The average fidelity displays
three different patterns corresponding to , and . For
each pattern, the average fidelity at time is independent of when the
system subjects to dissipative environment, and decreases as increases when
the system subjects to dephasing environment. The maximum concurrence also
decreases as increases, and when , it arrives at an
asymptotic value determined by the decoherence rate and the structure
of the spin network.Comment: 12 pages, 6 figure
Teleportation of the one-qubit state with environment-disturbed recovery operations
We study standard protocol for teleporting the one-qubit
state with both the transmission process of the two qubits constitute the
quantum channel and the recovery operations performed by Bob disturbed by the
decohering environment. The results revealed that Bob's imperfect operations do
not eliminate the possibility of nonclassical teleportation fidelity provided
he shares an ideal channel state with Alice, while the transmission process is
constrained by a critical time longer than which will result in
failure of if the two qubits are corrupted by the decohering
environment. Moreover, we found that under the condition of the same
decoherence rate , the teleportation protocol is significantly more
fragile when it is executed under the influence of the noisy environment than
those under the influence of the dissipative and dephasing environments.Comment: 8 pages, 4 figure
Control and manipulation of entanglement between two coupled qubits by fast pulses
We have investigated the analytical and numerical dynamics of entanglement
for two qubits that interact with each other via Heisenberg XXX-type
interaction and subject to local time-specific external kick and Gaussian
pulse-type magnetic fields in x-y plane. The qubits have been assumed to be
initially prepared in different pure separable and maximally entangled states
and the effect of the strength and the direction of external fast pulses on
concurrence has been investigated. The carefully designed kick or pulse
sequences are found to enable one to obtain constant long-lasting entanglement
with desired magnitude. Moreover, the time ordering effects are found to be
important in the creation and manipulation of entanglement by external fields.Comment: 18 pages, 6 figure
State transfer in intrinsic decoherence spin channels
By analytically solving the master equation, we investigate quantum state
transfer, creation and distribution of entanglement in the model of Milburn's
intrinsic decoherence. Our results reveal that the ideal spin channels will be
destroyed by the intrinsic decoherence environment, and the detrimental effects
become severe as the decoherence rate and the spin chain length
increase. For infinite evolution time, both the state transfer fidelity and the
concurrence of the created and distributed entanglement approach steady state
values, which are independent of the decoherence rate and decrease as
the spin chain length increases. Finally, we present two modified spin
chains which may serve as near perfect spin channels for long distance state
transfer even in the presence of intrinsic decoherence environments .Comment: 11 pages, 11 figure
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