355 research outputs found
Optimal discrimination of quantum states with a fixed rate of inconclusive outcomes
In this paper we present the solution to the problem of optimally
discriminating among quantum states, i.e., identifying the states with maximum
probability of success when a certain fixed rate of inconclusive answers is
allowed. By varying the inconclusive rate, the scheme optimally interpolates
between Unambiguous and Minimum Error discrimination, the two standard
approaches to quantum state discrimination. We introduce a very general method
that enables us to obtain the solution in a wide range of cases and give a
complete characterization of the minimum discrimination error as a function of
the rate of inconclusive answers. A critical value of this rate is identified
that coincides with the minimum failure probability in the cases where
unambiguous discrimination is possible and provides a natural generalization of
it when states cannot be unambiguously discriminated. The method is illustrated
on two explicit examples: discrimination of two pure states with arbitrary
prior probabilities and discrimination of trine states
Ab initio LSDA and LSDA+U study of pure and Cd-doped cubic lanthanide sesquioxides
The electronic, structural, and hyperfine properties of pure and Cd-doped lanthanide (Ln) sesquioxides with the cubic bixbyite structure (Ln2O3, Ln ranging from La to Lu) have been studied using the full-potential augmented plane wave plus local orbital (APW + lo) method within the local spin density approximation (LSDA) and the Coulomb-corrected LSDA + U. In the case of the pure systems, our calculations show that LSDA + U gives a better representation of the band structure compared to LSDA. The predicted equilibrium structures and the electric field gradient (EFG) tensor at Ln sites were calculated and compared with those obtained by means of hyperfine techniques and with theoretical results obtained in In2O3, Sc2O3, and Lu2O3 reported in the literature. The origin of the EFG at Ln sites and the role played by the 4f electrons on this quantity are discussed. In the case of the Cd-doped systems, the APW + lo method (also within LSDA and LSDA + U) was applied to treat the electronic structure of the doped system. The role of the Ln 4f electrons on the EFG at Cd impurity sites, and other variables like structural distortions induced by the Cd impurity, were investigated in detail and are discussed and compared with available experimental results. An excellent agreement between the experimental and calculated EFGs was found for all Cd-doped systems.Fil: Richard, Diego. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de FĂsica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de FĂsica La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de FĂsica; ArgentinaFil: Muñoz, Emiliano Luis. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de FĂsica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de FĂsica La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de FĂsica; ArgentinaFil: RenterĂa, Mario. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de FĂsica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de FĂsica La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de FĂsica; ArgentinaFil: Errico, Leonardo Antonio. Universidad Nacional del Noroeste de la Provincia de Buenos Aires; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de FĂsica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de FĂsica La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de FĂsica; ArgentinaFil: Svane, A.. University Aarhus. Institut for Fysik Og Astronomi; DinamarcaFil: Christensen, N. E.. University Aarhus. Institut for Fysik Og Astronomi; Dinamarc
PVpanel Sim 2.0 – PV Module Simulation with Improved Device Physics
Efficiency is a crucial parameter to consider when fabricating thin film (TF) photovoltaic panels because there is a significant efficiency drop between lab scale cells and large modules. PVpanel Sim is a circuit simulation using SPICE tool which combines the effects of the major reasons of efficiency reduction, like shunt leakages and sheet resistance, with external factors like irradiance and the effects of shadowing in order to provide the user with a better understanding of how a solar panel would behave. For the current version of the tool a basic equivalent model for individual cells is used with ideal components, this model is perfect for crystalline silicon (c-Si) solar cells but in order to efficiently simulate TF cells like amorphous silicon (a-Si) a different circuit model has to be incorporated. The model that is going to be used for a-Si cells includes two nonlinear voltage dependent current sources, representing photocurrent and recombination current; a diode, representing the dark current; for the shunt resistance a non-linear current source, depending on its own voltage and a conductance value, is used; and sheet resistance is included. The tool outputs include I-V and P-V plots as well as having the capability of giving 2D node voltage drop, 2D power generation, and shunt resistances plots that show how this values would change if shadowing is present or if photocurrent or shunt conductance differ. A more complete and realistic version of the tool is to be published taking into account the effects of the added changes
Decoherence assisting a measurement-driven quantum evolution process
We study the problem of driving an unknown initial mixed quantum state onto a
known pure state without using unitary transformations. This can be achieved,
in an efficient manner, with the help of sequential measurements on at least
two unbiased bases. However here we found that, when the system is affected by
a decoherence mechanism, only one observable is required in order to achieve
the same goal. In this way the decoherence can assist the process. We show
that, depending on the sort of decoherence, the process can converge faster or
slower than the method implemented by means of two complementary observables.Comment: Four pages, three figures included ([email protected]
Entanglement of distant atoms by projective measurement: The role of detection efficiency
We assess proposals for entangling two distant atoms by measurement of
emitted photons, analyzing how their performance depends on the photon
detection efficiency. We consider schemes based on measurement of one or two
photons and compare them in terms of the probability to obtain the detection
event and of the conditional fidelity with which the desired entangled state is
created. Based on an unravelling of the master equation, we quantify the
parameter regimes in which one or the other scheme is more efficient, including
the possible combination of the one-photon scheme with state purification. In
general, protocols based on one-photon detection are more efficient in set-ups
characterized by low photon detection efficiency, while at larger values
two-photon protocols are preferable. We give numerical examples based on
current experiments.Comment: 12 pages, 6 figure
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