6,860 research outputs found
Synchronized pulse control of decoherence
We present a new strategy for multipulse control over decoherence. When a
two-level system interacts with a reservoir characterized by a specific
frequency, we find that the decoherence is effectively suppressed by
synchronizing the pulse-train application with the dynamical motion of the
reservoir.Comment: 14 pages, 8 figure
Through a glass darkly: a case for the study of virtual space
This paper begins to examine the similarities and differences between virtual space and real space, as taken from anarchitectural (as opposed to a biological, psychological, geographic, philosophical or information theoretic)standpoint. It continues by introducing a number of criteria, suggested by the authors as being necessary for virtualspace to be used in a manner consistent with our experience of real space. Finally, it concludes by suggesting apedagogical framework for the benefits and associated learning outcomes of the study and examination of thisrelationship. This is accompanied by examples of recent student work, which set out to investigate this relationship
Independent and relative effects of stress, depressive symptoms, and affect on college students' daily health behaviors.
Stress and depressive symptoms are associated with maladaptive health behavior practices such as unhealthy eating, sedentary behavior, insufficient sleep, and substance use. The relative and interactive effects of stress and depressive symptoms on health behavior practices are less well understood. The present study examined these processes in a daily diary study of 127 college students. Results from hierarchical generalized linear models indicated that depressive symptoms, and chronic and daily stress, but not acute stressful life events, were significantly associated with a composite score of daily maladaptive health behavior engagement (depressive symptoms b = .01, SE= .00, p < .01; chronic stress, b = .03, SE= .01, p < .01; daily stress, b = .01, SE= .01, p = .02); unexpectedly, the effect of stress on health behaviors was not moderated by depressive symptoms. Additionally, results demonstrated that the effect of depressive symptoms on health behaviors was mediated by fluctuations in daily negative affect. These results bear implications for intervention during a crucial period in the development of mental and physical health
Decoherence Rates in Large Scale Quantum Computers and Macroscopic Systems
Markovian regime decoherence effects in quantum computers are studied in
terms of the fidelity for the situation where the number of qubits N becomes
large. A general expression giving the decoherence time scale in terms of
Markovian relaxation elements and expectation values of products of system
fluctuation operators is obtained, which could also be applied to study
decoherence in other macroscopic systems such as Bose condensates and
superconductors. A standard circuit model quantum computer involving
three-state lambda system ionic qubits is considered, with qubits localised
around well-separated positions via trapping potentials. The centre of mass
vibrations of the qubits act as a reservoir. Coherent one and two qubit gating
processes are controlled by time dependent localised classical electromagnetic
fields that address specific qubits, the two qubit gating processes being
facilitated by a cavity mode ancilla, which permits state interchange between
qubits. With a suitable choice of parameters, it is found that the decoherence
time can be made essentially independent of N.Comment: Minor revisions. To be published in J Mod Opt. One figur
Measuring Entangled Qutrits and Their Use for Quantum Bit Commitment
We produce and holographically measure entangled qudits encoded in transverse
spatial modes of single photons. With the novel use of a quantum state
tomography method that only requires two-state superpositions, we achieve the
most complete characterisation of entangled qutrits to date. Ideally, entangled
qutrits provide better security than qubits in quantum bit-commitment: we model
the sensitivity of this to mixture and show experimentally and theoretically
that qutrits with even a small amount of decoherence cannot offer increased
security over qubits.Comment: Paper updated to match published version; 5 pages, 4 figures, images
have been included at slightly lower quality for the archiv
Coherent optical control of correlation waves of spins in semiconductors
We calculate the dynamical fluctuation spectrum of electronic spins in a
semiconductor under a steady-state illumination by light containing
polarization squeezing correlations. Taking into account quasi-particle
lifetime and spin relaxation for this non-equilibrium situation we consider up
to fourth order optical effects which are sensitive to the squeezing phases.
We demonstrate the possibility to control the spin fluctuations by optically
modulating these phases as a function of frequency, leading to a non-Lorentzian
spectrum which is very different from the thermal equilibrium fluctuations in
n-doped semiconductors. Specifically, in the time-domain spin-spin correlation
can exhibit time delays and sign flips originating from the phase modulations
and correlations of polarizations, respectively. For higher light intensity we
expect a regime where the squeezing correlations will dominate the spectrum.Comment: 17 pages, 8 figure
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