37 research outputs found
Experimental verification of multipartite entanglement in quantum networks
Multipartite entangled states are a fundamental resource for a wide range of
quantum information processing tasks. In particular, in quantum networks it is
essential for the parties involved to be able to verify if entanglement is
present before they carry out a given distributed task. Here we design and
experimentally demonstrate a protocol that allows any party in a network to
check if a source is distributing a genuinely multipartite entangled state,
even in the presence of untrusted parties. The protocol remains secure against
dishonest behaviour of the source and other parties, including the use of
system imperfections to their advantage. We demonstrate the verification
protocol in a three- and four-party setting using polarization-entangled
photons, highlighting its potential for realistic photonic quantum
communication and networking applications.Comment: 8 pages, 4 figure
BSP Functional Programming: Examples of a Cost Based Methodology
Abstract. Bulk-Synchronous Parallel ML (BSML) is a functional data-parallel language for the implementation of Bulk-Synchronous Parallel (BSP) algorithms. It makes an estimation of the execution time (cost) possible. This paper presents some general examples of BSML programs and a comparison of their predicted costs with the measured execution time on a parallel machine
Benchmarking implementations of functional languages with ‘Pseudoknot', a float-intensive benchmark
Over 25 implementations of different functional languages are benchmarked using the same program, a floating-point intensive application taken from molecular biology. The principal aspects studied are compile time and execution time for the various implementations that were benchmarked. An important consideration is how the program can be modified and tuned to obtain maximal performance on each language implementation. With few exceptions, the compilers take a significant amount of time to compile this program, though most compilers were faster than the then current GNU C compiler (GCC version 2.5.8). Compilers that generate C or Lisp are often slower than those that generate native code directly: the cost of compiling the intermediate form is normally a large fraction of the total compilation time. There is no clear distinction between the runtime performance of eager and lazy implementations when appropriate annotations are used: lazy implementations have clearly come of age when it comes to implementing largely strict applications, such as the Pseudoknot program. The speed of C can be approached by some implementations, but to achieve this performance, special measures such as strictness annotations are required by non-strict implementations. The benchmark results have to be interpreted with care. Firstly, a benchmark based on a single program cannot cover a wide spectrum of ‘typical' applications. Secondly, the compilers vary in the kind and level of optimisations offered, so the effort required to obtain an optimal version of the program is similarly varie
Quantum key distribution based on orthogonal states allows secure quantum bit commitment
For more than a decade, it was believed that unconditionally secure quantum
bit commitment (QBC) is impossible. But basing on a previously proposed quantum
key distribution scheme using orthogonal states, here we build a QBC protocol
in which the density matrices of the quantum states encoding the commitment do
not satisfy a crucial condition on which the no-go proofs of QBC are based.
Thus the no-go proofs could be evaded. Our protocol is fault-tolerant and very
feasible with currently available technology. It reopens the venue for other
"post-cold-war" multi-party cryptographic protocols, e.g., quantum bit string
commitment and quantum strong coin tossing with an arbitrarily small bias. This
result also has a strong influence on the Clifton-Bub-Halvorson theorem which
suggests that quantum theory could be characterized in terms of
information-theoretic constraints.Comment: Published version plus an appendix showing how to defeat the
counterfactual attack, more references [76,77,90,118-120] cited, and other
minor change