Scaling of the Equilibrium Magnetization in the Mixed State of Type-II Superconductors

Landau, I. L.; Ott, H. R.

doi:10.1007/s10909-005-3922-3

Cited by 3 publications

(1 citation statement)

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“…For overdoped cuprates, thermodynamic characteristics reveal unambiguous evidence of the second-order phase transition at T c [18]. Similarly, analysis of Nernst effect [19], equilibrium [20] and fluctuation [21,22] magnetization and resistivity [23] reveal vanishing of H c2 (T → T c ) in a wide doping range. However, in underdoped cuprates, characterized by the persistence of the normal state pseudogap at T > T c , the superconducting transition at T c becomes obscured and both thermodynamic [18] and transport [24] properties become abnormal.…”

Section: Introductionmentioning

confidence: 83%

Temperature dependence of the bulk energy gap in underdopedBi2Sr2CaCu2O8+δ
Krasnov
¹

2009
Phys. Rev. B
49
9
43
0
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Understanding of the puzzling phenomenon of high temperature superconductivity requires reliable spectroscopic information about temperature dependence of the bulk electronic density of states. Here I present a comprehensive analysis of T −evolution of bulk electronic spectra in Bi-2212 obtained by Intrinsic Tunneling Spectroscopy on small mesa structures. Unambiguous spectroscopic information is obtained by obviation of self-heating problem and by improving the spectroscopic resolution. The obtained data indicate that the superconducting transition maintains the mean-field character down to moderate underdoping, and is associated with an abrupt opening of the superconducting gap, which is well described by the conventional BCS T −dependence. The mean-field critical temperature reaches maximum at the optimal doping and decreases with underdoping. Such behavior is inconsistent with theories assuming intimate connection between superconducting and antiferromagnetic spin gaps, and support proposals associating high temperature superconductivity with the presence of competing ground states and a quantum critical point near optimal doping.

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Section: Introductionmentioning

confidence: 83%

Temperature dependence of the bulk energy gap in underdopedBi2Sr2CaCu2O8+δ
Krasnov
¹

2009
Phys. Rev. B
49
9
43
0
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Two types of Hc2(T) dependences in Bi2Sr2Ca1−xYxCu2O8+δ with different Yttrium content

Landau

Keller

2007

Physica C: Superconductivity

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Single-Step Implementation of Universal Quantum Gates

Grigorenko

Khveshchenko

2005

Phys. Rev. Lett.

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We construct optimized implementations of the CNOT and other universal two-qubit gates that, unlike many of the previously proposed protocols, are carried out in a single step. The new protocols require tunable inter-qubit couplings but, in return, show a significant improvements in the quality of gate operations. Our optimization procedure can be further extended to the combinations of elementary two-qubit as well as irreducible many-qubit gates.According to one of the central results obtained in quantum information theory, an arbitrarily complex quantum protocol can be decomposed into a sequence of single-qubit rotations and two-qubit gates [1]. However, despite its providing a convenient means of designing logical circuits, in practice such a decomposition may not necessarily achieve the shortest possible times of operation and, consequently, the lowest possible decoherence rates. In any practical implementations, however, the latter are crucially important, for any realistic qubit system would always suffer a detrimental effect of its dissipative environment.Recently, there have been various attempts to improve the performance of universal quantum gates by searching for their optimal implementations among the entire class of two-qubit Hamiltonians with the most general time dependent coefficients. However, a typical outcome of such a tour-de-force variational search [2] tends to be a complicated sequence of highly irregular pulses whose physical content often remains largely obscure.In the search of a more sophisticated analytical approach, a number of authors invoked optimal control theory with the goal of implementing a desired unitary transformation independently of the initial state. The resulting complex system of nonlinear integral-differential equations can be solved numerically with the help of the Krotov or similar iterative algorithms [3].Conceivably, a significantly simpler alternative to the above approaches would be a straightforward implementation of a given unitary transformation in the smallest possible number of steps, during each of which the Hamiltonian remains constant. A well known example of this kind is provided by the two-qubit SWAP gate which can be readily implemented (up to a global phase) with the use of the spin-rotationally invariant Heisenberg inter-qubit coupling that remains constant during the gate operation.In this paper, we construct one-step implementations of some widely used universal gates. In contrast to the previous works where a constant decoherence rate was assumed and, therefore, the overall loss of coherence accumulated during a gate operation would be evaluated solely on the basis of its total duration, we quantify the adverse effect of the environment by actually solving the corresponding master equation for the density matrix of the coupled qubits. In this way, we account for the fact that the decoherence rates generally depend upon (and vary with) the adjustable parameters of the Hamiltonian.The problem of implementing a given unitary transformation in the co...

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Scaling of the Equilibrium Magnetization in the Mixed State of Type-II Superconductors

Cited by 3 publications

References 53 publications

Temperature dependence of the bulk energy gap in underdopedBi2Sr2CaCu2O8+δ
Krasnov
¹

2009
Phys. Rev. B
49
9
43
0
View full text Add to dashboard Cite

Temperature dependence of the bulk energy gap in underdopedBi2Sr2CaCu2O8+δ
Krasnov
¹

2009
Phys. Rev. B
49
9
43
0
View full text Add to dashboard Cite

Two types of Hc2(T) dependences in Bi2Sr2Ca1−xYxCu2O8+δ with different Yttrium content

Single-Step Implementation of Universal Quantum Gates

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Scaling of the Equilibrium Magnetization in the Mixed State of Type-II Superconductors

Cited by 3 publications

References 53 publications

Temperature dependence of the bulk energy gap in underdopedBi2Sr2CaCu2O8+δKrasnov1 2009Phys. Rev. B499430View full textAdd to dashboardCite

Temperature dependence of the bulk energy gap in underdopedBi2Sr2CaCu2O8+δKrasnov1 2009Phys. Rev. B499430View full textAdd to dashboardCite

Two types of Hc2(T) dependences in Bi2Sr2Ca1−xYxCu2O8+δ with different Yttrium content

Single-Step Implementation of Universal Quantum Gates

Contact Info

Product

Resources

About

Temperature dependence of the bulk energy gap in underdopedBi2Sr2CaCu2O8+δ
Krasnov
¹

2009
Phys. Rev. B
49
9
43
0
View full text Add to dashboard Cite

Temperature dependence of the bulk energy gap in underdopedBi2Sr2CaCu2O8+δ
Krasnov
¹

2009
Phys. Rev. B
49
9
43
0
View full text Add to dashboard Cite