4,450 research outputs found
Feynman graphs and the large dimensional limit of multipartite entanglement
We are interested in the properties of multipartite entanglement of a system
composed by -level parties (qudits).
Focussing our attention on pure states we want to tackle the problem of the
maximization of the entanglement for such systems. In particular we effort the
problem trying to minimize the purity of the system. It has been shown that not
for all systems this function can reach its lower bound, however it can be
proved that for all values of a can always be found such that the lower
bound can be reached.
In this paper we examine the high-temperature expansion of the distribution
function of the bipartite purity over all balanced bipartition considering its
optimization problem as a problem of statistical mechanics. In particular we
prove that the series characterizing the expansion converges and we analyze the
behavior of each term of the series as .Comment: 29 pages, 11 figure
Experimental Test of Two-way Quantum Key Distribution in Presence of Controlled Noise
We describe the experimental test of a quantum key distribution performed
with a two-way protocol without using entanglement. An individual incoherent
eavesdropping is simulated and induces a variable amount of noise on the
communication channel. This allows a direct verification of the agreement
between theory and practice.Comment: 4 pages, 3 figure
Lanifici e strumenti della produzione nell'Italia centro-meridionale
Plinio (Plin. nat. 35, 138) describes the lanificium as a place in quo properant omnium mulierum pensa. The ancient lanificia are difficult to recognize both on an architectural and functional point of view. Literary and epigraphical sources provide much information, but very few we know about their dislocation and the type of textile activities that were carried out inside them. Through an amount of samples in central-southern Italy of Republican and Imperial periods, this paper focuses on the archaeological evidences which could suggest the presence of such a building (in particular lanariae and textrina), on their architectures, or not architectures, and on the labour forces concentrated in lanificia
Assessment of a quantum phase gate operation based on nonlinear optics
We analyze in detail the proposal for a two-qubit gate for travelling
single-photon qubits recently presented by C. Ottaviani \emph{et al}. [Phys.
Rev. A \textbf{73}, 010301(R) (2006)]. The scheme is based on an ensemble of
five-level atoms coupled to two quantum and two classical light fields. The two
quantum fields undergo cross-phase modulation induced by electromagnetically
induced transparency. The performance of this two-qubit quantum phase gate for
travelling single-photon qubits is thoroughly examined in the steady-state and
transient regimes, by means of a full quantum treatment of the system dynamics.
In the steady-state regime, we find a general trade-off between the size of the
conditional phase shift and the fidelity of the gate operation. However, this
trade-off can be bypassed in the transient regime, where a satisfactory gate
operation is found to be possible, significantly reducing the gate operation
time.Comment: 12 pages, 15 figure
Single-photon three-qubit quantum logic using spatial light modulators
The information-carrying capacity of a single photon can be vastly expanded by exploiting its multiple degrees of freedom: spatial, temporal, and polarization. Although multiple qubits can be encoded per photon, to date only two-qubit single-photon quantum operations have been realized. Here, we report an experimental demonstration of three-qubit single-photon, linear, deterministic quantum gates that exploit photon polarization and the two-dimensional spatial-parity-symmetry of the transverse single-photon field. These gates are implemented using a polarization-sensitive spatial light modulator that provides a robust, non-interferometric, versatile platform for implementing controlled unitary gates. Polarization here represents the control qubit for either separable or entangling unitary operations on the two spatial-parity target qubits. Such gates help generate maximally entangled three-qubit Greenberger–Horne–Zeilinger and W states, which is confirmed by tomographical reconstruction of single-photon density matrices. This strategy provides access to a wide range of three-qubit states and operations for use in few-qubit quantum information processing protocols
Optomechanical sideband cooling of a thin membrane within a cavity
We present an experimental study of dynamical back-action cooling of the
fundamental vibrational mode of a thin semitransparent membrane placed within a
high-finesse optical cavity. We study how the radiation pressure interaction
modifies the mechanical response of the vibrational mode, and the experimental
results are in agreement with a Langevin equation description of the coupled
dynamics. The experiments are carried out in the resolved sideband regime, and
we have observed cooling by a factor 350 We have also observed the mechanical
frequency shift associated with the quadratic term in the expansion of the
cavity mode frequency versus the effective membrane position, which is
typically negligible in other cavity optomechanical devices.Comment: 15 pages, 7 figure
Systems engineering approach for pre-conceptual design of DEMO divertor cassette
Abstract This paper presents the pre-conceptual design activities conducted for the European DEMO divertor, focusing on cassette design and Plasma Facing Components (PFC) integration. Following the systems engineering principles, a systematic design method, the Iterative and Participative Axiomatic Design Process (IPADeP), has been adopted. Basing on Axiomatic Design, IPADeP supports the early conceptual design of complex systems. The work moved from the geometrical and interface constraints imposed by the 2015 DEMO configuration model. Then, since different materials will be used for cassette and PFCs, the divertor geometry has been developed taking into account the cooling parameters of the cassette Eurofer steel and the integration of PFCs cooling system. Accordingly, the design process led to a double wall cassette structure with internal reinforcing ribs to withstand cassette coolant pressure and three different kinds of piping schemes for PFCs with dual circuits. These three solutions differs in the feeding pipes layouts and target manifold protection and they have been proposed and evaluated considering heat flux issues, shielding problems, interface requirements with blanket and vacuum vessel and remote maintenance needs. A cassette parametric shell model has been used to perform first structural analyses of the cassette body against coolant pressure. Taking advantages of the parametric surface modelling and its linkage with Finite Element (FE) code, the cassette ribs layout and thickness has been evaluated and optimized, considering at the same time the structural strength needed to withstand the coolant parameters and the maximum stiffness required for cassette preloading and locking needs
Device-independent entanglement-based Bennett 1992 protocol
In this paper we set forth a novel connection between the Bennett 1992
protocol and a Bell inequality. This allows us to extend the usual
prepare-and-measure protocol to its entanglement-based formulation. We exploit
a recent result in the frame of device-independent quantum key distribution to
provide a simple, model-independent, security proof for the new protocol. The
minimum efficiency required for a practical implementation of the scheme is the
lowest reported to date.Comment: 7 pages, 3 figures. 3nd version: published versio
Observation of correlated-photon statistics using a single detector
We report experimental observations of correlated-photon statistics in the
single-photon detection rate. The usual quantum interference in a two-photon
polarization interferometer always accompanies a dip in the single detector
counting rate, regardless of whether a dip or peak is seen in the coincidence
rate. This effect is explained by taking into account all possible photon
number states that reach the detector, rather than considering just the state
post-selected by the coincidence measurement. We also report an
interferometeric scheme in which the interference peak or dip in coincidence
corresponds directly to a peak or dip in the single-photon detection rate.Comment: 4 pages, two-column (minor errors corrected.
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