26,496 research outputs found
Detection-Loophole-Free Test of Quantum Nonlocality, and Applications
We present a source of entangled photons that violates a Bell inequality free
of the "fair-sampling" assumption, by over 7 standard deviations. This
violation is the first experiment with photons to close the detection loophole,
and we demonstrate enough "efficiency" overhead to eventually perform a fully
loophole-free test of local realism. The entanglement quality is verified by
maximally violating additional Bell tests, testing the upper limit of quantum
correlations. Finally, we use the source to generate secure private quantum
random numbers at rates over 4 orders of magnitude beyond previous experiments.Comment: Main text: 5 pages, 2 figures, 1 table. Supplementary Information: 7
pages, 2 figure
Andreev Bound States in the Kondo Quantum Dots Coupled to Superconducting Leads
We have studied the Kondo quantum dot coupled to two superconducting leads
and investigated the subgap Andreev states using the NRG method. Contrary to
the recent NCA results [Clerk and Ambegaokar, Phys. Rev. B 61, 9109 (2000);
Sellier et al., Phys. Rev. B 72, 174502 (2005)], we observe Andreev states both
below and above the Fermi level.Comment: 5 pages, 5 figure
Generalised Hong-Ou-Mandel Experiments with Bosons and Fermions
The Hong-Ou-Mandel (HOM) dip plays an important role in recent linear optics
experiments. It is crucial for quantum computing with photons and can be used
to characterise the quality of single photon sources and linear optics setups.
In this paper, we consider generalised HOM experiments with bosons or
fermions passing simultaneously through a symmetric Bell multiport beam
splitter. It is shown that for even numbers of bosons, the HOM dip occurs
naturally in the coincidence detection in the output ports. In contrast,
fermions always leave the setup separately exhibiting perfect coincidence
detection. Our results can be used to verify or employ the quantum statistics
of particles experimentally.Comment: 11 pages, 2 figures, more references adde
Isotropic singularity in inhomogeneous brane cosmological models
We discuss the asymptotic dynamical evolution of spatially inhomogeneous
brane-world cosmological models close to the initial singularity. By
introducing suitable scale-invariant dependent variables and a suitable gauge,
we write the evolution equations of the spatially inhomogeneous brane
cosmological models with one spatial degree of freedom as a system of
autonomous first-order partial differential equations. We study the system
numerically, and we find that there always exists an initial singularity, which
is characterized by the fact that spatial derivatives are dynamically
negligible. More importantly, from the numerical analysis we conclude that
there is an initial isotropic singularity in all of these spatially
inhomogeneous brane cosmologies for a range of parameter values which include
the physically important cases of radiation and a scalar field source. The
numerical results are supported by a qualitative dynamical analysis and a
calculation of the past asymptotic decay rates. Although the analysis is local
in nature, the numerics indicates that the singularity is isotropic for all
relevant initial conditions. Therefore this analysis, and a preliminary
investigation of general inhomogeneous () models, indicates that it is
plausible that the initial singularity is isotropic in spatially inhomogeneous
brane-world cosmological models and consequently that brane cosmology naturally
gives rise to a set of initial data that provide the conditions for inflation
to subsequently take place.Comment: 32 pages with 8 pictures. submitted to Class. Quant. Gra
Comparing different approaches for generating random numbers device-independently using a photon pair source
What is the most efficient way to generate random numbers
device-independently using a photon pair source based on spontaneous parametric
down conversion (SPDC)? We consider this question by comparing two
implementations of a detection-loophole-free Bell test. In particular, we study
in detail a scenario where a heralded single photon source (HSPS) is used to
herald path-entangled states, i.e. entanglement between two spatial modes
sharing a single photon and where non-locality is revealed using photon
counting preceded by small displacement operations. We start by giving a
theoretical description of such a measurement. We then show how to optimize the
Bell-CHSH violation through a non-perturbative calculation, taking the main
experimental imperfections into account. We finally bound the amount of
randomness that can be extracted and compare it to the one obtained with the
conventional scenario using photon pairs entangled e.g. in polarization and
analyzed through photon counting. While the former requires higher overall
detection efficiencies, it is far more efficient in terms of both the entropy
per experimental run and the rate of random bit generation.Comment: 12 pages, 5 figure
Experimental realization of strange nonchaotic attractors in a quasiperiodically forced electronic circuit
We have identified the three prominent routes, namely Heagy-Hammel,
fractalization and intermittency routes, and their mechanisms for the birth of
strange nonchaotic attractors (SNAs) in a quasiperiodically forced electronic
system constructed using a negative conductance series LCR circuit with a diode
both numerically and experimentally. The birth of SNAs by these three routes is
verified from both experimental and their corresponding numerical data by
maximal Lyapunov exponents, and their variance, Poincar\'e maps, Fourier
amplitude spectrum, spectral distribution function and finite-time Lyapunov
exponents. Although these three routes have been identified numerically in
different dynamical systems, the experimental observation of all these
mechanisms is reported for the first time to our knowledge and that too in a
single second order electronic circuit.Comment: 21 figure
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