70 research outputs found
Comment on "Quantum dense key distribution"
In this Comment we question the security of recently proposed by Degiovanni
et al. [Phys. Rev. A 69 (2004) 032310] scheme of quantum dense key
distribution
Eavesdropping on the "ping-pong" quantum communication protocol
The proposed eavesdropping scheme reveals that the quantum communication
protocol recently presented by Bostrom and Felbinger [Phys. Rev. Lett. 89,
187902 (2002)] is not secure as far as quantum channel losses are taken into
account
Discrete Time Quantum Walk Approach to State Transfer
We show that a quantum state transfer, previously studied as a continuous
time process in networks of interacting spins, can be achieved within the model
of discrete time quantum walks with position dependent coin. We argue that due
to additional degrees of freedom, discrete time quantum walks allow to observe
effects which cannot be observed in the corresponding continuous time case.
First, we study a discrete time version of the engineered coupling protocol due
to Christandl et. al. [Phys. Rev. Lett. 92, 187902 (2004)] and then discuss the
general idea of conversion between continuous time quantum walks and discrete
time quantum walks.Comment: 9 pages, 6 figures, comments welcom
How to encode the states of two non-entangled qubits in one qutrit?
A new scheme of quantum coding is presented. The scheme concerns the quantum
states to which Schumacher's compression does not apply. It is shown that two
qubits can be encoded in a single qutrit in such a way that one can faithfully
reconstruct the state of one qubit. Decision on which of these two qubits is to
be reconstructed can be made long after the encoding took place. The scheme
succeeds with the average probability of 2/3.Comment: 7 page
Superluminal observers do not explain quantum superpositions
The quantum description of reality is quite different from the classical one.
Understanding this difference at a fundamental level is still an interesting
topic. Recently, Dragan and Ekert [New J. Phys. 22 (2020) 033038] postulated
that considering so-called superluminal observers can be useful in this
context. In particular, they claim that the full mathematical structure of the
generalized Lorentz transformation may imply the emergence of multiple quantum
mechanical trajectories. On the contrary, here we show that the generalized
Lorentz transformation, when used in a consistent way, does not provide any
correspondence between the classical concept of a definite path and the
multiple paths of quantum mechanics.Comment: 4 pages, new section adde
Quantum walk as a generalized measuring device
We show that a one-dimensional discrete time quantum walk can be used to
implement a generalized measurement in terms of positive operator value measure
(POVM) on a single qubit. More precisely, we show that for a single qubit any
set of rank 1 and rank 2 POVM elements can be generated by a properly
engineered quantum walk. In such a scenario the measurement of particle at
position x=i corresponds to a measurement of a POVM element E_i on a qubit. We
explicitly construct quantum walks implementing unambiguous state
discrimination and SIC-POVM.Comment: 6 pages, 1 figur
Probabilistic coding of quantum states
We discuss properties of probabilistic coding of two qubits to one qutrit and
generalize the scheme to higher dimensions. We show that the protocol
preservers entanglement between qubits to be encoded and environment and can be
also applied to mixed states. We present the protocol which enables encoding of
n qudits to one qudit of dimension smaller than the Hilbert space of the
original system and then probabilistically but error-free decode any subset of
k qudits. We give a formula for the probability of successful decoding
New data on the late Badenian-Sarmatian depositsof the Nowy Sącz Basin (Magura Nappe, Polish Outer Carpathians) and their palaeogeographical implications
In the Nowy Sącz Basin, newly exposed Middle Miocene deposits have been studied and sam pled in the Kamienica Nawojowska, Poprad
and Dunajec rivers. The calcareous nannoplankton of the fresh water to marine deposits was examined. Pale grey and brown clayey shales
with plant remains and thin seams of lignite represent the freshwater deposits of the Biegonice Formation. These deposits pass upwards
into ca. 50 m thick packet of brackish and marine deposits, represented mainly by dark marly shales with bivalves and gastropods of the
Iwkowa and Niskowa formations. These deposits contain relatively rich late Badenian to Sarmatian calcareous nannoplakton (NN6/7Zone)
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