9,506 research outputs found
Entanglement dynamics of two-qubit system in different types of noisy channels
In this paper, we study entanglement dynamics of a two-qubit extended
Werner-like state locally interacting with independent noisy channels, i.e.,
amplitude damping, phase damping and depolarizing channels. We show that the
purity of initial entangled state has direct impacts on the entanglement
robustness in each noisy channel. That is, if the initial entangled state is
prepared in mixed instead of pure form, the state may exhibit entanglement
sudden death (ESD) and/or be decreased for the critical probability at which
the entanglement disappear.Comment: 11 pages, 6 figure
Entanglement and quantum phase transition in alternating XY spin chain with next-nearest neighbour interactions
By using the method of density-matrix renormalization-group to solve the
different spin-spin correlation functions, the nearest-neighbouring
entanglement(NNE) and next-nearest-neighbouring entanglement(NNNE) of
one-dimensional alternating Heisenberg XY spin chain is investigated in the
presence of alternating nearest neighbour interactions of exchange couplings,
external magnetic fields and next-nearest neighbouring interactions. For
dimerized ferromagnetic spin chain, NNNE appears only above the critical
dimerized interaction, meanwhile, the dimerized interaction effects quantum
phase transition point and improves NNNE to a large value. We also study the
effect of ferromagnetic or antiferromagnetic next-nearest neighboring (NNN)
interactions on the dynamics of NNE and NNNE. The ferromagnetic NNN interaction
increases and shrinks NNE below and above critical frustrated interaction
respectively, while the antiferromagnetic NNN interaction always decreases NNE.
The antiferromagnetic NNN interaction results to a larger value of NNNE in
comparison to the case when the NNN interaction is ferromagnetic.Comment: 13 pages, 4 figures,. accepted by Chinese Physics B 2008 11 (in
press
Competition between the BCS superconductivity and ferromagnetic spin fluctuations in MgCNi
The low temperature specific heat of the superconductor MgCNi and a
non-superconductor MgCNi is investigated in detail. An additional
contribution is observed from the data of MgCNi but absent in
MgCNi, which is demonstrated to be insensitive to the applied
magnetic field even up to 12 Tesla. A detailed discussion on its origin is then
presented. By subtracting this additional contribution, the zero field specific
heat of MgCNi can be well described by the BCS theory with the gap ratio
() determined by the previous tunneling measurements. The
conventional s-wave pairing state is further proved by the magnetic field
dependence of the specific heat at low temperatures and the behavior of the
upper critical field.Comment: To appear in Physical Review B, 6 pages, 7 figure
The entanglement in one-dimensional random XY spin chain with Dzyaloshinskii-Moriya interaction
The impurities of exchange couplings, external magnetic fields and
Dzyaloshinskii--Moriya (DM) interaction considered as Gaussian distribution,
the entanglement in one-dimensional random spin systems is investigated by
the method of solving the different spin-spin correlation functions and the
average magnetization per spin. The entanglement dynamics at central locations
of ferromagnetic and antiferromagnetic chains have been studied by varying the
three impurities and the strength of DM interaction. (i) For ferromagnetic spin
chain, the weak DM interaction can improve the amount of entanglement to a
large value, and the impurities have the opposite effect on the entanglement
below and above critical DM interaction. (ii) For antiferromagnetic spin chain,
DM interaction can enhance the entanglement to a steady value. Our results
imply that DM interaction strength, the impurity and exchange couplings (or
magnetic field) play competing roles in enhancing quantum entanglement.Comment: 12 pages, 3 figure
Evidence for s-wave pairing from measurement on lower critical field in
Magnetization measurements in the low field region have been carefully
performed on a well-shaped cylindrical and an ellipsoidal sample of
superconductor . Data from both samples show almost the same results.
The lower critical field and the London penetration depth
are thus derived. It is found that the result of normalized superfluid density
of can be well described by BCS
prediction with the expectation for an isotropic s-wave superconductivity.Comment: To appear in Phys. Rev.
Entanglement control in one-dimensional random XY spin chain
The entanglement in one-dimensional random XY spin systems where the
impurities of exchange couplings and the external magnetic fields are
considered as random variables is investigated by solving the different
spin-spin correlation functions and the average magnetization per spin. The
entanglement dynamics near particular locations of the system is also studied
when the exchange couplings (or the external magnetic fields) satisfy three
different distributions(the Gaussian distribution, double-Gaussian
distribution, and bimodal distribution). We find that the entanglement can be
controlled by varying the strength of external magnetic field and the different
distributions of impurities. Moreover, the entanglement of some
nearest-neighboring qubits can be increased for certain parameter values of the
three different distributions.Comment: 13 pages, 4 figure
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