341 research outputs found
Electron Fabry-Perot interferometer with two entangled magnetic impurities
We consider a one-dimensional (1D) wire along which single conduction
electrons can propagate in the presence of two spin-1/2 magnetic impurities.
The electron may be scattered by each impurity via a contact-exchange
interaction and thus a spin-flip generally occurs at each scattering event.
Adopting a quantum waveguide theory approach, we derive the stationary states
of the system at all orders in the electron-impurity exchange coupling
constant. This allows us to investigate electron transmission for arbitrary
initial states of the two impurity spins. We show that for suitable electron
wave vectors, the triplet and singlet maximally entangled spin states of the
impurities can respectively largely inhibit the electron transport or make the
wire completely transparent for any electron spin state. In the latter case, a
resonance condition can always be found, representing an anomalous behaviour
compared to typical decoherence induced by magnetic impurities. We provide an
explanation for these phenomena in terms of the Hamiltonian symmetries.
Finally, a scheme to generate maximally entangled spin states of the two
impurities via electron scattering is proposed.Comment: 19 page
Entanglement-induced electron coherence in a mesoscopic ring with two magnetic impurities
We investigate the Aharonov-Bohm (AB) interference pattern in the electron
transmission through a mesoscopic ring in which two identical non-interacting
magnetic impurities are embedded. Adopting a quantum waveguide theory, we
derive the exact transmission probability amplitudes and study the influence of
maximally entangled states of the impurity spins on the electron transmittivity
interference pattern. For suitable electron wave vectors, we show that the
amplitude of AB oscillations in the absence of impurities is in fact not
reduced within a wide range of the electron-impurity coupling constant when the
maximally entangled singlet state is prepared. Such state is thus able to
inhibit the usual electron decoherence due to scattering by magnetic
impurities. We also show how this maximally entangled state of the impurity
spins can be generated via electron scattering.Comment: 8 page
Effect of Static Disorder in an Electron Fabry-Perot Interferometer with Two Quantum Scattering Centers
In a recent paper -- F. Ciccarello \emph{et al.}, New J. Phys. \textbf{8},
214 (2006) -- we have demonstrated that the electron transmission properties of
a one-dimensional (1D) wire with two identical embedded spin-1/2 impurities can
be significantly affected by entanglement between the spins of the scattering
centers. Such effect is of particular interest in the control of transmission
of quantum information in nanostructures and can be used as a detection scheme
of maximally entangled states of two localized spins. In this letter, we relax
the constraint that the two magnetic impurities are equal and investigate how
the main results presented in the above paper are affected by a static disorder
in the exchange coupling constants of the impurities. Good robustness against
deviation from impurity symmetry is found for both the entanglement dependent
transmission and the maximally entangled states generation scheme.Comment: 4 pages, 5 figure
Physical model for the generation of ideal resources in multipartite quantum networking
We propose a physical model for generating multipartite entangled states of
spin- particles that have important applications in distributed quantum
information processing. Our protocol is based on a process where mobile spins
induce the interaction among remote scattering centers. As such, a major
advantage lies on the management of stationary and well separated spins. Among
the generable states, there is a class of -qubit singlets allowing for
optimal quantum telecloning in a scalable and controllable way. We also show
how to prepare Aharonov, W and Greenberger-Horne-Zeilinger states.Comment: 5 pages, 2 figures. Format revise
Management of direct oral anticoagulants in patients with atrial fibrillation undergoing cardioversion
Atrial fibrillation the most common cardiac arrhythmia. Its incidence rises steadily with each decade, becoming a real "epidemic phenomenon". Cardioversion is defined as a rhythm control strategy which, if successful, restores normal sinus rhythm. This, whether obtained with synchronized shock or with drugs, involves a periprocedural risk of stroke and systemic embolism which is reduced by adequate anticoagulant therapy in the weeks before or by the exclusion of left atrial thrombi. Direct oral anticoagulants are safe, manageable, and provide rapid onset of oral anticoagulation; they are an important alternative to heparin/warfarin from all points of view, with a considerable reduction in bleedings and increase in the safety and quality of life of patients
Implementing quantum gates through scattering between a static and a flying qubit
We investigate whether a two-qubit quantum gate can be implemented in a
scattering process involving a flying and a static qubit. To this end, we focus
on a paradigmatic setup made out of a mobile particle and a quantum impurity,
whose respective spin degrees of freedom couple to each other during a
one-dimensional scattering process. Once a condition for the occurrence of
quantum gates is derived in terms of spin-dependent transmission coefficients,
we show that this can be actually fulfilled through the insertion of an
additional narrow potential barrier. An interesting observation is that under
resonance conditions the above enables a gate only for isotropic Heisenberg
(exchange) interactions and fails for an XY interaction. We show the existence
of parameter regimes for which gates able to establish a maximum amount of
entanglement can be implemented. The gates are found to be robust to variations
of the optimal parameters.Comment: 7 pages, 3 figure
LEO object’s light-curve acquisition system and their inversion for attitude reconstruction
In recent years, the increase in space activities has brought the space debris issue to the top of the list of all space agencies. The fact of there being uncontrolled objects is a problem both for the operational satellites in orbit (avoiding collisions) and for the safety of people on the ground (re-entry objects). Optical systems provide valuable assistance in identifying and monitoring such objects. The Sapienza Space System and Space Surveillance (S5Lab) has been working in this field for years, being able to take advantage of a network of telescopes spread over different continents. This article is focused on the re-entry phase of the object; indeed, the knowledge of the state of the object, in terms of position, velocity, and attitude during the descent, is crucial in order to predict as accurately as possible the impact point on the ground. A procedure to retrieve the light curves of orbiting objects by means of optical data will be shown and a method to obtain the attitude determination from their inversion based on a stochastic optimization (genetic algorithm) will be proposed
Entanglement Controlled Single-Electron Transmittivity
We consider a system consisting of single electrons moving along a 1D wire in
the presence of two magnetic impurities. Such system shows strong analogies
with a Fabry - Perot interferometer in which the impurities play the role of
two mirrors with a quantum degree of freedom: the spin. We have analysed the
electron transmittivity of the wire in the presence of entanglement between the
impurity spins. The main result of our analysis is that, for suitable values of
the electron momentum, there are two maximally entangled state of the impurity
spins the first of which makes the wire transparent whatever the electron spin
state while the other strongly inhibits the electron transmittivity. Such
predicted striking effect is experimentally observable with present day
technology.Comment: Published version (6 figures
Optical observations for energetic characterization of in-orbit explosion: the FREGAT-SB case
Over the past years, the constant increase of space debris and inactive satellites is the root cause of catastrophic events, such as collision between a debris and active satellites. One of the events that might generate a large number of debris is the in-orbit explosion. Within this complex framework, it is of paramount importance to use a monitoring and surveillance system in order to understand the number and the distribution of fragments, in an area around the Earth extremely populated by man-made object. This entails a growing international interest in Space Surveillance and Tracking (SST), where optical observation reaches an interesting method to obtain information of orbital objects. In this paper, the Sapienza Space Systems and Space Surveillance Laboratory (S5Lab) presents the results of an observative campaign focused on the energetical characterization of the explosion and the monitoring of the fragments, which have been generated by a low orbit explosion of the third Russian stage rocket FREGAT-SB (ID 37756). The event occurred on 08.05.2020 between 04:00 and 06:00 UTC time. Through the observatory system Sapienza Coupled University Debris Observatory (SCUDO) located in Collepardo (FR, Italy), a certain number of images have been collected. The observation strategy was focused on the orbital plane to try to estimate the number of these fragments and their distribution. Once the astrometry phase to retrieve the measures in terms of right ascension and declination was performed, a first analysis is carried on to understand whether or not the fragments are already present in the North American Aerospace Defense Command (NORAD) catalogue. The ones that are not catalogued could be FREGAT’s fragments. The next energetic characterization method is based on a tangential impulse assignment in agreement with isotropic explosion and the evolution of fragments’ cloud, where the important variations, to a first approximation, are on semiaxes and eccentricity. As a result of this procedure, an association between the impulse and the measure takes place. The analysis of the angular distance between original body and the fragments over the time is carried out, in order to validate this method. Moreover, a magnitude estimation procedure is shown. All these results are compared with those obtained with the NORAD assignment
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