1,855,810 research outputs found
Symmetric minimal quantum tomography by successive measurements
We consider the implementation of a symmetric informationally complete
probability-operator measurement (SIC POM) in the Hilbert space of a d-level
system by a two-step measurement process: a diagonal-operator measurement with
high-rank outcomes, followed by a rank-1 measurement in a basis chosen in
accordance with the result of the first measurement. We find that any
Heisenberg-Weyl group-covariant SIC POM can be realized by such a sequence
where the second measurement is simply a measurement in the Fourier basis,
independent of the result of the first measurement. Furthermore, at least for
the particular cases studied, of dimension 2, 3, 4, and 8, this scheme reveals
an unexpected operational relation between mutually unbiased bases and SIC
POMs; the former are used to construct the latter. As a laboratory application
of the two-step measurement process, we propose feasible optical experiments
that would realize SIC POMs in various dimensions.Comment: 7 pages, 2 figure
The ultimate quantum limits on the accuracy of measurements
A quantum generalization of rate-distortion theory from standard communication and information theory is developed for application to determining the ultimate performance limit of measurement systems in physics. For the estimation of a real or a phase parameter, it is shown that the root-mean-square error obtained in a measurement with a single-mode photon level N cannot do better than approximately N exp -1, while approximately exp(-N) may be obtained for multi-mode fields with the same photon level N. Possible ways to achieve the remarkable exponential performance are indicated
Coherent population trapping in a dressed two-level atom via a bichromatic field
We show theoretically that by applying a bichromatic electromagnetic field,
the dressed states of a monochromatically driven two-level atom can be pumped
into a coherent superposition termed as dressed-state coherent population
trapping. Such effect can be viewed as a new doorknob to manipulate a two-level
system via its control over dressed-state populations. Application of this
effect in the precision measurement of Rabi frequency, the unexpected
population inversion and lasing without inversion are discussed to demonstrate
such controllability.Comment: 14 pages, 6 figure
Diffusion length measurements using the scanning electron microscope
A measurement technique employing the scanning electron microscope is described in which values of the true bulk diffusion length are obtained. It is shown that surface recombination effects can be eliminated through the application of highly doped surface field layers. The influence of high injection level effects and low-high junction current generation on the resulting measurement was investigated. Close agreement is found between the diffusion lengths measured by this method and those obtained using a penetrating radiation technique
Experimental realization of a measurement conditional unitary operation at single photon level and application to detector characterization
Our last experimental results on the realization of a measurement-conditional
unitary operation at single photon level are presented. This gate operates by
rotating by the polarization of a photon produced by means of Type-II
Parametric Down Conversion conditional to a polarization measurement on the
correlated photon. We then propose a new scheme for measuring the quantum
efficiency of a single photon detection apparatus by using this set-up. We
present experimental results obtained with this scheme compared with {\it
traditional} biphoton calibration. Our results show the interesting
potentiality of the suggested scheme.Comment: to appear in Proc. of SPIE meeting, Denver august 200
Quantum measurement of a mesoscopic spin ensemble
We describe a method for precise estimation of the polarization of a
mesoscopic spin ensemble by using its coupling to a single two-level system.
Our approach requires a minimal number of measurements on the two-level system
for a given measurement precision. We consider the application of this method
to the case of nuclear spin ensemble defined by a single electron-charged
quantum dot: we show that decreasing the electron spin dephasing due to nuclei
and increasing the fidelity of nuclear-spin-based quantum memory could be
within the reach of present day experiments.Comment: 8 pages, 2 figures; minor changes, published versio
An LLVM Instrumentation Plug-in for Score-P
Reducing application runtime, scaling parallel applications to higher numbers
of processes/threads, and porting applications to new hardware architectures
are tasks necessary in the software development process. Therefore, developers
have to investigate and understand application runtime behavior. Tools such as
monitoring infrastructures that capture performance relevant data during
application execution assist in this task. The measured data forms the basis
for identifying bottlenecks and optimizing the code. Monitoring infrastructures
need mechanisms to record application activities in order to conduct
measurements. Automatic instrumentation of the source code is the preferred
method in most application scenarios. We introduce a plug-in for the LLVM
infrastructure that enables automatic source code instrumentation at
compile-time. In contrast to available instrumentation mechanisms in
LLVM/Clang, our plug-in can selectively include/exclude individual application
functions. This enables developers to fine-tune the measurement to the required
level of detail while avoiding large runtime overheads due to excessive
instrumentation.Comment: 8 page
Temperature and heat flux measurements: Challenges for high temperature aerospace application
The measurement of high temperatures and the influence of heat transfer data is not strictly a problem of either the high temperatures involved or the level of the heating rates to be measured at those high temperatures. It is a problem of duration during which measurements are made and the nature of the materials in which the measurements are made. Thermal measurement techniques for each application must respect and work with the unique features of that application. Six challenges in the development of measurement technology are discussed: (1) to capture the character and localized peak values within highly nonuniform heating regions; (2) to manage large volumes of thermal instrumentation in order to efficiently derive critical information; (3) to accommodate thermal sensors into practical flight structures; (4) to broaden the capabilities of thermal survey techniques to replace discrete gages in flight and on the ground; (5) to provide supporting instrumentation conduits which connect the measurement points to the thermally controlled data acquisition system; and (6) to develop a class of 'vehicle tending' thermal sensors to assure the integrity of flight vehicles in an efficient manner
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