22,899 research outputs found
Scheme for direct measurement of a general two-qubit Hamiltonian
The construction of two-qubit gates appropriate for universal quantum
computation is of enormous importance to quantum information processing.
Building such gates is dependent on accurate knowledge of the interaction
dynamics between two qubit systems. This letter will present a systematic
method for reconstructing the full two-qubit interaction Hamiltonian through
experimental measures of concurrence. This not only gives a convenient method
for constructing two qubit quantum gates, but can also be used to
experimentally determine various Hamiltonian parameters in physical systems. We
show explicitly how this method can be employed to determine the first and
second order spin-orbit corrections to the exchange coupling in quantum dots.Comment: 4 Pages, 1 Figur
Cryogenic propellant management: Integration of design, performance and operational requirements
The integration of the design features of the Shuttle elements into a cryogenic propellant management system is described. The implementation and verification of the design/operational changes resulting from design deficiencies and/or element incompatibilities encountered subsequent to the critical design reviews are emphasized. Major topics include: subsystem designs to provide liquid oxygen (LO2) tank pressure stabilization, LO2 facility vent for ice prevention, liquid hydrogen (LH2) feedline high point bleed, pogo suppression on the Space Shuttle Main Engine (SSME), LO2 low level cutoff, Orbiter/engine propellant dump, and LO2 main feedline helium injection for geyser prevention
Majorana spinors and extended Lorentz symmetry in four-dimensional theory
An extended local Lorentz symmetry in four-dimensional (4D) theory is
considered. A source of this symmetry is a group of general linear
transformations of four-component Majorana spinors GL(4,M) which is isomorphic
to GL(4,R) and is the covering of an extended Lorentz group in a 6D Minkowski
space M(3,3) including superluminal and scaling transformations. Physical
space-time is assumed to be a 4D pseudo-Riemannian manifold. To connect the
extended Lorentz symmetry in the M(3,3) space with the physical space-time, a
fiber bundle over the 4D manifold is introduced with M(3,3) as a typical fiber.
The action is constructed which is invariant with respect to both general 4D
coordinate and local GL(4,M) spinor transformations. The components of the
metric on the 6D fiber are expressed in terms of the 4D pseudo-Riemannian
metric and two extra complex fields: 4D vector and scalar ones. These extra
fields describe in the general case massive particles interacting with an extra
U(1) gauge field and weakly interacting with ordinary particles, i.e.
possessing properties of invisible (dark) matter.Comment: 24 page
Semi-analytical dark matter halos and the Jeans equation
Although N-body studies of dark matter halos show that the density profiles,
rho(r), are not simple power-laws, the quantity rho/sigma^3, where sigma(r) is
the velocity dispersion, is in fact a featureless power-law over ~3 decades in
radius. In the first part of the paper we demonstrate, using the semi-analytic
Extended Secondary Infall Model (ESIM), that the nearly scale-free nature of
rho/sigma^3 is a robust feature of virialized halos in equilibrium. By
examining the processes in common between numerical N-body and semi-analytic
approaches, we argue that the scale-free nature of rho/sigma^3 cannot be the
result of hierarchical merging, rather it must be an outcome of violent
relaxation. The empirical results of the first part of the paper motivate the
analytical work of the second part of the paper, where we use rho/sigma^3
proportional to r^{-alpha} as an additional constraint in the isotropic Jeans
equation of hydrostatic equilibrium. Our analysis shows that the constrained
Jeans equation has different types of solutions, and in particular, it admits a
unique ``periodic'' solution with alpha=1.9444. We derive the analytic
expression for this density profile, which asymptotes to inner and outer
profiles of rho ~ r^{-0.78}, and rho ~ r^{-3.44}, respectively.Comment: 37 pg, 14 fig. Accepted to ApJ: added two figures and extended
discussion. Note that an earlier related paper (conference proceedings)
astro-ph/0412442 has a mistake in eq.(2.2); the correct version is eq.(5) of
the present submissio
How the asymmetry of internal potential influences the shape of I-V characteristic of nanochannels
Ion transport in biological and synthetic nanochannels is characterized by
such phenomena as ion current fluctuations, rectification, and pumping.
Recently, it has been shown that the nanofabricated synthetic pores could be
considered as analogous to biological channels with respect to their transport
characteristics \cite{Apel, Siwy}. The ion current rectification is analyzed.
Ion transport through cylindrical nanopores is described by the Smoluchowski
equation. The model is considering the symmetric nanopore with asymmetric
charge distribution. In this model, the current rectification in asymmetrically
charged nanochannels shows a diode-like shape of characteristic. It is
shown that this feature may be induced by the coupling between the degree of
asymmetry and the depth of internal electric potential well. The role of
concentration gradient is discussed
Equivariant Formal Group Laws
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135640/1/plms0355.pd
Rare earth spin ensemble magnetically coupled to a superconducting resonator
Interfacing superconducting quantum processors, working in the GHz frequency
range, with optical quantum networks and atomic qubits is a challenging task
for the implementation of distributed quantum information processing as well as
for quantum communication. Using spin ensembles of rare earth ions provide an
excellent opportunity to bridge microwave and optical domains at the quantum
level. In this letter, we demonstrate magnetic coupling of Er spins
doped in YSiO crystal to a high-Q coplanar superconducting
resonator.Comment: 5 pages, 3 figure
Quantum System Identification by Bayesian Analysis of Noisy Data: Beyond Hamiltonian Tomography
We consider how to characterize the dynamics of a quantum system from a
restricted set of initial states and measurements using Bayesian analysis.
Previous work has shown that Hamiltonian systems can be well estimated from
analysis of noisy data. Here we show how to generalize this approach to systems
with moderate dephasing in the eigenbasis of the Hamiltonian. We illustrate the
process for a range of three-level quantum systems. The results suggest that
the Bayesian estimation of the frequencies and dephasing rates is generally
highly accurate and the main source of errors are errors in the reconstructed
Hamiltonian basis.Comment: 6 pages, 3 figure
Quantum phase transitions in photonic cavities with two-level systems
Systems of coupled photonic cavities have been predicted to exhibit quantum
phase transitions by analogy with the Hubbard model. To this end, we have
studied topologies of few (up to six) photonic cavities each containing a
single two-level system. Quantum phase space diagrams are produced for these
systems, and compared to mean-field results. We also consider finite effective
temperature, and compare this to the notion of disorder. We find the extent of
the Mott lobes shrink analogously to the conventional Bose-Hubbard model.Comment: 11 pages, 11 figures, updated typo
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