3,147 research outputs found
Quantum correlations from local amplitudes and the resolution of the Einstein-Podolsky-Rosen nonlocality puzzle
The Einstein-Podolsky-Rosen nonlocality puzzle has been recognized as one of
the most important unresolved issues in the foundational aspects of quantum
mechanics. We show that the problem is resolved if the quantum correlations are
calculated directly from local quantities which preserve the phase information
in the quantum system. We assume strict locality for the probability amplitudes
instead of local realism for the outcomes, and calculate an amplitude
correlation function.Then the experimentally observed correlation of outcomes
is calculated from the square of the amplitude correlation function. Locality
of amplitudes implies that the measurement on one particle does not collapse
the companion particle to a definite state. Apart from resolving the EPR
puzzle, this approach shows that the physical interpretation of apparently
`nonlocal' effects like quantum teleportation and entanglement swapping are
different from what is usually assumed. Bell type measurements do not change
distant states. Yet the correlations are correctly reproduced, when measured,
if complex probability amplitudes are treated as the basic local quantities. As
examples we discuss the quantum correlations of two-particle maximally
entangled states and the three-particle GHZ entangled state.Comment: Std. Latex, 11 pages, 1 table. Prepared for presentation at the
International Conference on Quantum Optics, ICQO'2000, Minsk, Belaru
Using of small-scale quantum computers in cryptography with many-qubit entangled states
We propose a new cryptographic protocol. It is suggested to encode
information in ordinary binary form into many-qubit entangled states with the
help of a quantum computer. A state of qubits (realized, e.g., with photons) is
transmitted through a quantum channel to the addressee, who applies a quantum
computer tuned to realize the inverse unitary transformation decoding of the
message. Different ways of eavesdropping are considered, and an estimate of the
time needed for determining the secret unitary transformation is given. It is
shown that using even small quantum computers can serve as a basis for very
efficient cryptographic protocols. For a suggested cryptographic protocol, the
time scale on which communication can be considered secure is exponential in
the number of qubits in the entangled states and in the number of gates used to
construct the quantum network
Graviton mass and total relative density of mass Omega_tot in Universe
It is noticed that the total relative density of mass in the Universe
Omega_tot should exceed 1, i.e. Omega_tot=1+f^2/6 according to the field
relativistic theory of gravity (RTG), which is free of the cosmological
singularity and which provides the Euclidean character for the 3-dimensional
space. Here f is the ratio of the graviton mass m_g to the contemporary value
of the ``Hubble mass'' m^0_H=\hbar H_0/c^2\simeq 3,8\cdot 10^{-66}h(g)
(h=0,71\pm0,07). Applying results of the experimental data processing presented
in [1] an upper limit for the graviton mass is established as m_g\leq 3,2\cdot
10^{-66}g at the 95% confidence level.Comment: 8 pages, latex fil
Current Models of Investor State Dispute Settlement Are Bad for Health: The European Union Could Offer an Alternative Comment on "The Trans-Pacific Partnership: Is It Everything We Feared for Health?"
In this commentary, we endorse concerns about the health impact of the trans-pacific partnership (TPP), paying particular attention to its mechanisms for investor state dispute settlement. We then describe the different, judge-led approach being advocated by the European Commission team negotiating the Trans-Atlantic Trade and Investment Partnership, arguing that, while not perfect, it offers significant advantages
Entangled photon pairs produced by a quantum dot strongly coupled to a microcavity
We show theoretically that entangled photon pairs can be produced on demand
through the biexciton decay of a quantum dot strongly coupled to the modes of a
photonic crystal. The strong coupling allows to tune the energy of the mixed
exciton-photon (polariton) eigenmodes, and to overcome the natural splitting
existing between the exciton states coupled with different linear polarizations
of light. Polariton states are moreover well protected against dephasing due to
their lifetime ten to hundred times shorter than that of a bare exciton. Our
analysis shows that the scheme proposed can be achievable with the present
technology
Evolution of a global string network in a matter dominated universe
We evolve the network of global strings in the matter-dominated universe by
means of numerical simulations. The existence of the scaling solution is
confirmed as in the radiation-dominated universe but the scaling parameter
takes a slightly smaller value, , which is
defined as with the energy density of
global strings and the string tension per unit length. The change of
from the radiation to the matter-dominated universe is consistent with
that obtained by Albrecht and Turok by use of the one-scale model. We also
study the loop distribution function and find that it can be well fitted with
that predicted by the one-scale model, where the number density of
the loop with the length is given by with and . Thus, the evolution of the
global string network in the matter-dominated universe can be well described by
the one-scale model as in the radiation-dominated universe.Comment: 10 pages, 5 figure
Scaling Property of the global string in the radiation dominated universe
We investigate the evolution of the global string network in the radiation
dominated universe by use of numerical simulations in 3+1 dimensions. We find
that the global string network settles down to the scaling regime where the
energy density of global strings, , is given by with the string tension per unit length and the scaling parameter,
, irrespective of the cosmic time. We also find that the
loop distribution function can be fitted with that predicted by the so-called
one scale model. Concretely, the number density, , of the loop with
the length, , is given by
where and is related with the Nambu-Goldstone(NG)
boson radiation power from global strings, , as with
. Therefore, the loop production function also scales and
the typical scale of produced loops is nearly the horizon distance. Thus, the
evolution of the global string network in the radiation dominated universe can
be well described by the one scale model in contrast with that of the local
string network.Comment: 18 pages, 9 figures, to appear in Phys. Rev.
Quantum complexities of ordered searching, sorting, and element distinctness
We consider the quantum complexities of the following three problems:
searching an ordered list, sorting an un-ordered list, and deciding whether the
numbers in a list are all distinct. Letting N be the number of elements in the
input list, we prove a lower bound of \frac{1}{\pi}(\ln(N)-1) accesses to the
list elements for ordered searching, a lower bound of \Omega(N\log{N}) binary
comparisons for sorting, and a lower bound of \Omega(\sqrt{N}\log{N}) binary
comparisons for element distinctness. The previously best known lower bounds
are {1/12}\log_2(N) - O(1) due to Ambainis, \Omega(N), and \Omega(\sqrt{N}),
respectively. Our proofs are based on a weighted all-pairs inner product
argument.
In addition to our lower bound results, we give a quantum algorithm for
ordered searching using roughly 0.631 \log_2(N) oracle accesses. Our algorithm
uses a quantum routine for traversing through a binary search tree faster than
classically, and it is of a nature very different from a faster algorithm due
to Farhi, Goldstone, Gutmann, and Sipser.Comment: This new version contains new results. To appear at ICALP '01. Some
of the results have previously been presented at QIP '01. This paper subsumes
the papers quant-ph/0009091 and quant-ph/000903
Third quantization of -type gravity
We examine the third quantization of -type gravity, based on its
effective Lagrangian in the case of a flat Friedmann-Lemaitre-Robertson-Walker
metric. Starting from the effective Lagrangian, we execute a suitable change of
variable and the second quantization, and we obtain the Wheeler-DeWitt
equation. The third quantization of this theory is considered. And the
uncertainty relation of the universe is investigated in the example of
-type gravity, where . It is shown, when the time is late
namely the scale factor of the universe is large, the spacetime does not
contradict to become classical, and, when the time is early namely the scale
factor of the universe is small, the quantum effects are dominating.Comment: 9 pages, Arbitrary constants in (4.19) are changed to arbitrary
functions of . Conclusions are not changed. References are added.
Typos are correcte
Geometry of the 3-Qubit State, Entanglement and Division Algebras
We present a generalization to 3-qubits of the standard Bloch sphere
representation for a single qubit and of the 7-dimensional sphere
representation for 2 qubits presented in Mosseri {\it et
al.}\cite{Mosseri2001}. The Hilbert space of the 3-qubit system is the
15-dimensional sphere , which allows for a natural (last) Hopf
fibration with as base and as fiber. A striking feature is, as in
the case of 1 and 2 qubits, that the map is entanglement sensitive, and the two
distinct ways of un-entangling 3 qubits are naturally related to the Hopf map.
We define a quantity that measures the degree of entanglement of the 3-qubit
state. Conjectures on the possibility to generalize the construction for higher
qubit states are also discussed.Comment: 12 pages, 2 figures, final versio
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