390 research outputs found
Multiparticle Bell's inequalities involving many measurement settings
We present a prescription for obtaining Bell's inequalities for N>2 observers
involving more than two alternative measurement settings. We give examples of
some families of such inequalities. The inequalities are violated by certain
classes of states for which all standard Bell's inequalities with two
measurement settings per observer are satisfied.Comment: 4 pages, RevTeX
From Cooperative Scans to Predictive Buffer Management
In analytical applications, database systems often need to sustain workloads
with multiple concurrent scans hitting the same table. The Cooperative Scans
(CScans) framework, which introduces an Active Buffer Manager (ABM) component
into the database architecture, has been the most effective and elaborate
response to this problem, and was initially developed in the X100 research
prototype. We now report on the the experiences of integrating Cooperative
Scans into its industrial-strength successor, the Vectorwise database product.
During this implementation we invented a simpler optimization of concurrent
scan buffer management, called Predictive Buffer Management (PBM). PBM is based
on the observation that in a workload with long-running scans, the buffer
manager has quite a bit of information on the workload in the immediate future,
such that an approximation of the ideal OPT algorithm becomes feasible. In the
evaluation on both synthetic benchmarks as well as a TPC-H throughput run we
compare the benefits of naive buffer management (LRU) versus CScans, PBM and
OPT; showing that PBM achieves benefits close to Cooperative Scans, while
incurring much lower architectural impact.Comment: VLDB201
Quantum Cryptography using larger alphabets
Like all of quantum information theory, quantum cryptography is traditionally
based on two level quantum systems. In this letter, a new protocol for quantum
key distribution based on higher dimensional systems is presented. An
experimental realization using an interferometric setup is also proposed.
Analyzing this protocol from the practical side, one finds an increased key
creation rate while keeping the initial laser pulse rate constant. Analyzing it
for the case of intercept/resend eavesdropping strategy, an increased error
rate is found compared to two dimensional systems, hence an advantage for the
legitimate users to detect an eavesdropper.Comment: 12 pages, 2 (eps) figure
Full separability criterion for tripartite quantum systems
In this paper, an intuitive approach is employed to generalize the full
separability criterion of tripartite quantum states of qubits to the
higher-dimensional systems (Phys. Rev. A \textbf{72}, 022333 (2005)). A
distinct characteristic of the present generalization is that less restrictive
conditions are needed to characterize the properties of full separability.
Furthermore, the formulation for pure states can be conveniently extended to
the case of mixed states by utilizing the kronecker product approximate
technique. As applications, we give the analytic approximation of the criterion
for weakly mixed tripartite quantum states and investigate the full
separability of some weakly mixed states.Comment: 5 pages. To be published in Europ. J.
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