610 research outputs found
New Protocols and Lower Bound for Quantum Secret Sharing with Graph States
We introduce a new family of quantum secret sharing protocols with limited
quantum resources which extends the protocols proposed by Markham and Sanders
and by Broadbent, Chouha, and Tapp. Parametrized by a graph G and a subset of
its vertices A, the protocol consists in: (i) encoding the quantum secret into
the corresponding graph state by acting on the qubits in A; (ii) use a
classical encoding to ensure the existence of a threshold. These new protocols
realize ((k,n)) quantum secret sharing i.e., any set of at least k players
among n can reconstruct the quantum secret, whereas any set of less than k
players has no information about the secret. In the particular case where the
secret is encoded on all the qubits, we explore the values of k for which there
exists a graph such that the corresponding protocol realizes a ((k,n)) secret
sharing. We show that for any threshold k> n-n^{0.68} there exists a graph
allowing a ((k,n)) protocol. On the other hand, we prove that for any k<
79n/156 there is no graph G allowing a ((k,n)) protocol. As a consequence there
exists n_0 such that the protocols introduced by Markham and Sanders admit no
threshold k when the secret is encoded on all the qubits and n>n_0
Quantum Speedup by Quantum Annealing
We study the glued-trees problem of Childs et. al. in the adiabatic model of
quantum computing and provide an annealing schedule to solve an oracular
problem exponentially faster than classically possible. The Hamiltonians
involved in the quantum annealing do not suffer from the so-called sign
problem. Unlike the typical scenario, our schedule is efficient even though the
minimum energy gap of the Hamiltonians is exponentially small in the problem
size. We discuss generalizations based on initial-state randomization to avoid
some slowdowns in adiabatic quantum computing due to small gaps.Comment: 7 page
The Real Combination Problem : Panpsychism, Micro-Subjects, and Emergence
Panpsychism harbors an unresolved tension, the seriousness of which has yet to be fully appreciated. I capture this tension as a dilemma, and offer panpsychists advice on how to resolve it. The dilemma, briefly, is as follows. Panpsychists are committed to the perspicuous explanation of macro-mentality in terms of micro-mentality. But panpsychists take the micro-material realm to feature not just mental properties, but also micro-subjects to whom these properties belong. Yet it is impossible to explain the constitution of a macro-subject (like one of us) in terms of the assembly of micro-subjects, for, I show, subjects cannot combine. Therefore the panpsychist explanatory project is derailed by the insistence that the worldâs ultimate material constituents (ultimates) are subjects of experience. The panpsychist faces a choice of abandoning her explanatory project, or recanting the claim that the ultimates are subjects. This is the dilemma. I argue that the latter option is to be preferred. This neednât constitute a wholesale abandonment of panpsychism, however, since panpsychists can maintain that the ultimates possess phenomenal qualities, despite not being subjects of those qualities. This proposal requires us to make sense of phenomenal qualities existing independently of experiencing subjects, a challenge I tackle in the penultimate section. The position eventually reached is a form of neutral monism, so another way to express the overall argument is to say that, keeping true to their philosophical motivations, panpsychists should really be neutral monists.Peer reviewedFinal Accepted Versio
Extending scientific computing system with structural quantum programming capabilities
We present a basic high-level structures used for developing quantum
programming languages. The presented structures are commonly used in many
existing quantum programming languages and we use quantum pseudo-code based on
QCL quantum programming language to describe them. We also present the
implementation of introduced structures in GNU Octave language for scientific
computing. Procedures used in the implementation are available as a package
quantum-octave, providing a library of functions, which facilitates the
simulation of quantum computing. This package allows also to incorporate
high-level programming concepts into the simulation in GNU Octave and Matlab.
As such it connects features unique for high-level quantum programming
languages, with the full palette of efficient computational routines commonly
available in modern scientific computing systems. To present the major features
of the described package we provide the implementation of selected quantum
algorithms. We also show how quantum errors can be taken into account during
the simulation of quantum algorithms using quantum-octave package. This is
possible thanks to the ability to operate on density matrices
Four Photon Entanglement from Down Conversion
Double-pair emission from type-II parametric down conversion results in a
highly entangled 4-photon state. Due to interference, which is similar to
bunching from thermal emission, this state is not simply a product of two
pairs. The observation of this state can be achieved by splitting the two
emission modes at beam splitters and subsequent detection of a photon in each
output. Here we describe the features of this state and give a Bell theorem for
a 4-photon test of local realistic hidden variable theories.Comment: 5 pages, 1 figure, submitted to PR
Hiding bits in Bell states
We present a scheme for hiding bits in Bell states that is secure even when
the sharers Alice and Bob are allowed to carry out local quantum operations and
classical communication. We prove that the information that Alice and Bob can
gain about a hidden bit is exponentially small in , the number of qubits in
each share, and can be made arbitrarily small for hiding multiple bits. We
indicate an alternative efficient low-entanglement method for preparing the
shared quantum states. We discuss how our scheme can be implemented using
present-day quantum optics.Comment: 4 pages RevTex, 1 figure, various small changes and additional
paragraph on optics implementatio
The Spitzer Space Telescope Mission
The Spitzer Space Telescope, NASA's Great Observatory for infrared astronomy,
was launched 2003 August 25 and is returning excellent scientific data from its
Earth-trailing solar orbit. Spitzer combines the intrinsic sensitivity
achievable with a cryogenic telescope in space with the great imaging and
spectroscopic power of modern detector arrays to provide the user community
with huge gains in capability for exploration of the cosmos in the infrared.
The observatory systems are largely performing as expected and the projected
cryogenic lifetime is in excess of 5 years. This paper summarizes the on-orbit
scientific, technical and operational performance of Spitzer. Subsequent papers
in this special issue describe the Spitzer instruments in detail and highlight
many of the exciting scientific results obtained during the first six months of
the Spitzer mission.Comment: Accepted for publication in the Astrophyscial Journal Supplement
Spitzer Special Issue, 22 pages, 3 figures. Higher resolution versions of the
figures are available at http://ssc.spitzer.caltech.edu/pubs/journal2004.htm
Characterizing two solar-type Kepler subgiants with asteroseismology: KIC10920273 and KIC11395018
Determining fundamental properties of stars through stellar modeling has
improved substantially due to recent advances in asteroseismology. Thanks to
the unprecedented data quality obtained by space missions, particularly CoRoT
and Kepler, invaluable information is extracted from the high-precision stellar
oscillation frequencies, which provide very strong constraints on possible
stellar models for a given set of classical observations. In this work, we have
characterized two relatively faint stars, KIC10920273 and KIC11395018, using
oscillation data from Kepler photometry and atmospheric constraints from
ground-based spectroscopy. Both stars have very similar atmospheric properties;
however, using the individual frequencies extracted from the Kepler data, we
have determined quite distinct global properties, with increased precision
compared to that of earlier results. We found that both stars have left the
main sequence and characterized them as follows: KIC10920273 is a
one-solar-mass star (M=1.00 +/- 0.04 M_sun), but much older than our Sun
(t=7.12 +/- 0.47 Gyr), while KIC11395018 is significantly more massive than the
Sun (M=1.27 +/- 0.04 M_sun) with an age close to that of the Sun (t=4.57 +/-
0.23 Gyr). We confirm that the high lithium abundance reported for these stars
should not be considered to represent young ages, as we precisely determined
them to be evolved subgiants. We discuss the use of surface lithium abundance,
rotation and activity relations as potential age diagnostics.Comment: 12 pages, 3 figures, 5 tables. Accepted by Ap
Toward scalable quantum computation with cavity QED systems
We propose a scheme for quantum computing using high-Q cavities in which the
qubits are represented by single cavity modes restricted in the space spanned
by the two lowest Fock states. We show that single qubit operations and
universal multiple qubit gates can be implemented using atoms sequentially
crossing the cavities.Comment: 14 pages, 8 figure
Quantum key distribution via quantum encryption
A quantum key distribution protocol based on quantum encryption is presented
in this Brief Report. In this protocol, the previously shared
Einstein-Podolsky-Rosen pairs act as the quantum key to encode and decode the
classical cryptography key. The quantum key is reusable and the eavesdropper
cannot elicit any information from the particle Alice sends to Bob. The concept
of quantum encryption is also discussed.Comment: 4 Pages, No Figure. Final version to appear in PR
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