2,487 research outputs found
Guidance and Control in a Josephson Charge Qubit
In this paper we propose a control strategy based on a classical guidance law
and consider its use for an example system: a Josephson charge qubit. We
demonstrate how the guidance law can be used to attain a desired qubit state
using the standard qubit control fields.Comment: 9 pages, 5 figure
Signatures of the collapse and revival of a spin Schr\"{o}dinger cat state in a continuously monitored field mode
We study the effects of continuous measurement of the field mode during the
collapse and revival of spin Schr\"{o}dinger cat states in the Tavis-Cummings
model of N qubits (two-level quantum systems) coupled to a field mode. We show
that a compromise between relatively weak and relatively strong continuous
measurement will not completely destroy the collapse and revival dynamics while
still providing enough signal-to-noise resolution to identify the signatures of
the process in the measurement record. This type of measurement would in
principle allow the verification of the occurrence of the collapse and revival
of a spin Schr\"{o}dinger cat state.Comment: 5 pages, 2 figure
Nonlinear backreaction in a quantum mechanical SQUID
In this paper we discuss the coupling between a quantum mechanical
superconducting quantum interference device (SQUID) and an applied static
magnetic field. We demonstrate that the backreaction of a SQUID on the applied
field can interfere with the ability to bias the SQUID at values of the static
(DC) magnetic flux at, or near to, transitions in the quantum mechanical SQUID.Comment: 9 pages, to be published in Phys. Rev.
Leaf reflectance-nitrogen-chlorophyll relations among three south Texas woody rangeland plant species
Annual variations in the nitrogen-chlorophyll leaf reflectance of hackberry, honey mesquite and live oak in south Texas, were compared. In spring, leaf reflectance at the 0.55 m wavelength and nitrogen (N) concentration was high but leaf chlorophyll (chl) concentrations were low. In summer, leaf reflectance and N-concentration were low but lead chl concentrations were high. Linear correlations for both spring and summer of leaf reflectance with N and chl concentration or deviations from linear regression were not statistically significant
Comparison of LANDSAT-2 and field spectrometer reflectance signatures of south Texas rangeland plant communities
The accuracy was assessed for an atmospheric correction method that depends on clear water bodies to infer solar and atmospheric parameters for radiative transfer equations by measuring the reflectance signature of four prominent south Texas rangeland plants with the LANDSAT satellite multispectral scanner (MSS) and a ground based spectroradiometer. The rangeland plant reflectances produced by the two sensors were correlated with no significant deviation of the slope from unity or of the intercept from zero. These results indicated that the atmospheric correction produced LANDSAT MSS estimates of rangeland plant reflectances that are as accurate as the ground based spectroradiometer
Cool for Cats
The iconic Schr\"odinger's cat state describes a system that may be in a
superposition of two macroscopically distinct states, for example two clearly
separated oscillator coherent states. Quite apart from their role in
understanding the quantum classical boundary, such states have been suggested
as offering a quantum advantage for quantum metrology, quantum communication
and quantum computation. As is well known these applications have to face the
difficulty that the irreversible interaction with an environment causes the
superposition to rapidly evolve to a mixture of the component states in the
case that the environment is not monitored. Here we show that by engineering
the interaction with the environment there exists a large class of systems that
can evolve irreversibly to a cat state. To be precise we show that it is
possible to engineer an irreversible process so that the steady state is close
to a pure Schr\"odinger's cat state by using double well systems and an
environment comprising two-photon (or phonon) absorbers. We also show that it
should be possible to prolong the lifetime of a Schr\"odinger's cat state
exposed to the destructive effects of a conventional single-photon decohering
environment. Our protocol should make it easier to prepare and maintain
Schr\"odinger cat states which would be useful in applications of quantum
metrology and information processing as well as being of interest to those
probing the quantum to classical transition.Comment: 10 pages, 7 figures. Significantly updated version with supplementary
informatio
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