1,149 research outputs found
Coherent transfer of light polarization to electron spins in a semiconductor
We demonstrate that the superposition of light polarization states is
coherently transferred to electron spins in a semiconductor quantum well. By
using time-resolved Kerr rotation we observe the initial phase of Larmor
precession of electron spins whose coherence is transferred from light. To
break the electron-hole spin entanglement, we utilized the big discrepancy
between the transverse g-factors of electrons and light holes. The result
encourages us to make a quantum media converter between flying photon qubits
and stationary electron spin qubits in semiconductors.Comment: 4 pages. Submitted to Physical Review Letter
Decoherence of localized spins interacting via RKKY interaction
We theoretically study decoherence of two localized spins interacting via the
RKKY interaction in one-, two-, and three-dimensional electron gas. We derive
the kinetic equation for the reduced density matrix of the localized spins and
show that energy relaxation caused by singlet-triplet transition is suppressed
when the RKKY interaction is ferromagnetic. We also estimate the decoherence
time of the system consisting of two quantum dots embedded in a two dimensional
electron gas.Comment: 4pages, 2figure
Effect of exchange interaction on fidelity of quantum state transfer from a photon qubit to an electron-spin qubit
We analyzed the fidelity of the quantum state transfer (QST) from a
photon-polarization qubit to an electron-spin-polarization qubit in a
semiconductor quantum dot, with special attention to the exchange interaction
between the electron and the simultaneously created hole. In order to realize a
high-fidelity QST we had to separate the electron and hole as soon as possible,
since the electron-hole exchange interaction modifies the orientation of the
electron spin. Thus, we propose a double-dot structure to separate the electron
and hole quickly, and show that the fidelity of the QST can reach as high as
0.996 if the resonant tunneling condition is satisfied.Comment: 5 pages, 4 figures, to be published in Phys. Rev. B Rapid
Communication
Long-time behavior of MHD shell models
The long time behavior of velocity-magnetic field alignment is numerically
investigated in the framework of MHD shell model. In the stationary forced
case, the correlation parameter C displays a nontrivial behavior with long
periods of high variability which alternates with periods of almost constant C.
The temporal statistics of correlation is shown to be non Poissonian, and the
pdf of constant sign periods displays clear power law tails. The possible
relevance of the model for geomagnetic dynamo problem is discussed.Comment: 6 pages with 5 figures. In press on Europhysics Letter
On the generalized Hamiltonian structure of 3D dynamical systems
The Poisson structures for 3D systems possessing one constant of motion can
always be constructed from the solution of a linear PDE. When two constants of
the motion are available the problem reduces to a quadrature and the structure
functions include an arbitrary function of them
Asymmetric polarity reversals, bimodal field distribution, and coherence resonance in a spherically symmetric mean-field dynamo model
Using a mean-field dynamo model with a spherically symmetric helical
turbulence parameter alpha which is dynamically quenched and disturbed by
additional noise, the basic features of geomagnetic polarity reversals are
shown to be generic consequences of the dynamo action in the vicinity of
exceptional points of the spectrum. This simple paradigmatic model yields long
periods of constant polarity which are interrupted by self-accelerating field
decays leading to asymmetric polarity reversals. It shows the recently
discovered bimodal field distribution, and it gives a natural explanation of
the correlation between polarity persistence time and field strength. In
addition, we find typical features of coherence resonance in the dependence of
the persistence time on the noise.Comment: 5 pages, 7 figure
Coherent Interaction of Spins Induced by Thermal Bosonic Environment
We obtain and analyze the indirect exchange interaction between two two-state
systems, e.g., spins, in a formulation that also incorporates the quantum noise
that they experience, due to a bosonic environment, for instance, phonons. We
utilize a perturbative approach to obtain a quantum evolution equation for the
two-spin dynamics. A non-perturbative approach is used to study the onset of
the induced interaction, which is calculated exactly. We predict that for low
enough temperatures the interaction is coherent over time scales sufficient to
create entanglement, dominated by the zero-point quantum fluctuations of the
environment. We identify the time scales for which the spins develop
entanglement for various spatial separations.Comment: 10 pages, 3 figures; typos correcte
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