1,770 research outputs found

    Quasistationary quaternionic Hamiltonians and complex stochastic maps

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    We show that the complex projections of time-dependent η\eta -quasianti-Hermitian quaternionic Hamiltonian dynamics are complex stochastic dynamics in the space of complex quasi-Hermitian density matrices if and only if a quasistationarity condition is fulfilled, i. e., if and only if η\eta is an Hermitian positive time-independent complex operator. An example is also discussed.Comment: Submitted to J. Phys. A on October 25 200

    Quantum Discord and Quantum Computing - An Appraisal

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    We discuss models of computing that are beyond classical. The primary motivation is to unearth the cause of nonclassical advantages in computation. Completeness results from computational complexity theory lead to the identification of very disparate problems, and offer a kaleidoscopic view into the realm of quantum enhancements in computation. Emphasis is placed on the `power of one qubit' model, and the boundary between quantum and classical correlations as delineated by quantum discord. A recent result by Eastin on the role of this boundary in the efficient classical simulation of quantum computation is discussed. Perceived drawbacks in the interpretation of quantum discord as a relevant certificate of quantum enhancements are addressed.Comment: To be published in the Special Issue of the International Journal of Quantum Information on "Quantum Correlations: entanglement and beyond." 11 pages, 4 figure

    One qubit almost completely reveals the dynamics of two

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    From the time dependence of states of one of them, the dynamics of two interacting qubits is determined to be one of two possibilities that differ only by a change of signs of parameters in the Hamiltonian. The only exception is a simple particular case where several parameters in the Hamiltonian are zero and one of the remaining nonzero parameters has no effect on the time dependence of states of the one qubit. The mean values that describe the initial state of the other qubit and of the correlations between the two qubits also are generally determined to within a change of signs by the time dependence of states of the one qubit, but with many more exceptions. An example demonstrates all the results. Feedback in the equations of motion that allows time dependence in a subsystem to determine the dynamics of the larger system can occur in both classical and quantum mechanics. The role of quantum mechanics here is just to identify qubits as the simplest objects to consider and specify the form that equations of motion for two interacting qubits can take.Comment: 6 pages with new and updated materia

    Completely Positive Maps and Classical Correlations

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    We expand the set of initial states of a system and its environment that are known to guarantee completely positive reduced dynamics for the system when the combined state evolves unitarily. We characterize the correlations in the initial state in terms of its quantum discord [H. Ollivier and W. H. Zurek, Phys. Rev. Lett. 88, 017901 (2001)]. We prove that initial states that have only classical correlations lead to completely positive reduced dynamics. The induced maps can be not completely positive when quantum correlations including, but not limited to, entanglement are present. We outline the implications of our results to quantum process tomography experiments.Comment: 4 pages, 1 figur

    Single-electron quantum dot in Si/SiGe with integrated charge-sensing

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    Single-electron occupation is an essential component to measurement and manipulation of spin in quantum dots, capabilities that are important for quantum information processing. Si/SiGe is of interest for semiconductor spin qubits, but single-electron quantum dots have not yet been achieved in this system. We report the fabrication and measurement of a top-gated quantum dot occupied by a single electron in a Si/SiGe heterostructure. Transport through the quantum dot is directly correlated with charge-sensing from an integrated quantum point contact, and this charge-sensing is used to confirm single-electron occupancy in the quantum dot.Comment: 3 pages, 3 figures, accepted version, to appear in Applied Physics Letter

    Genetic identity of Tormalabaricus(Jerdon)(Teleostei : Cyprinidae) as revealed by RAPD markers

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    Tor malabaricus (Jerdon) is a mahseer species endemic to the Western Ghats. Since its original description, taxonomic position of the species has been extremely confusing. In the present study, Random Amplified polymorphic DNA (RAPD) markers were used to determine the taxonomic status of T.malabaricus collected from Balamore River, Tamil Nadu, India, by comparing its RAPD profile with that of Tor khudreee.15 random oligodecamers were used to amplify DNA from Tor malabaricus and Tor khudree (n=30 each) collected from two geographically isolated localities and a total of 119 amphicons were detected
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