18 research outputs found
TESTING THE QUANTUM-CLASSICAL BOUNDARY AND DIMENSIONALITY OF QUANTUM SYSTEMS
Ph.DDOCTOR OF PHILOSOPH
Approaching Tsirelson's bound in a photon pair experiment
Quantum theory introduces a cut between the observer and the observed system,
but does not provide a definition of what is an observer. Based on an
informational definition of observer, Grinbaum has recently predicted an upper
bound on bipartite correlations in the Clauser-Horne-Shimony-Holt (CHSH) Bell
scenario equal to 2.82537, which is slightly smaller than the Tsirelson bound
of standard quantum theory, but is consistent with all the available
experimental results. Not being able to exceed Grinbaum's limit would support
that quantum theory is only an effective description of a more fundamental
theory and would have a deep impact in physics and quantum information
processing. Here we present a test of the CHSH Bell inequality on photon pairs
in maximally entangled states of polarization in which a value 2.82759+-0.00051
is observed, violating Grinbaum's bound by 4.3 standard deviations and
providing the smallest distance with respect to Tsirelson's bound ever
reported, namely, 0.00084+-0.00051. This sets a new lower experimental bound
for Tsirelson's bound, strengthening the value of principles that predict
Tsirelson's bound as possible explanations of all natural limits of
correlations, and has important consequences for cryptographic security,
randomness certification, characterization of physical properties in
device-independent scenarios, and certification of quantum computation.Comment: 4 pages, 2 figures, 1 number - updated error bars, references, and
error discussio
Probing quantum-classical boundary with compression software
We experimentally demonstrate that it is impossible to simulate quantum
bipartite correlations with a deterministic universal Turing machine. Our
approach is based on the Normalized Information Distance (NID) that allows the
comparison of two pieces of data without detailed knowledge about their origin.
Using NID, we derive an inequality for output of two local deterministic
universal Turing machines with correlated inputs. This inequality is violated
by correlations generated by a maximally entangled polarization state of two
photons. The violation is shown using a freely available lossless compression
program. The presented technique may allow to complement the common statistical
interpretation of quantum physics by an algorithmic one.Comment: 7 pages, 6 figure
Eliminating Spectral Distinguishability in Ultrafast Spontaneous Parametric Down-conversion
Generation of polarization-entangled photon pairs with a precise timing
through down-conversion of femtosecond pulses is often faced with a degraded
polarization entanglement quality. In a previous experiment we have shown that
this degradation is induced by spectral distinguishability between the two
decay paths, in accordance with theoretical predictions. Here, we present an
experimental study of the spectral compensation scheme proposed and first
implemented by Kim et al. in 2002. By measuring the joint spectral properties
of the polarization correlations of the photon pairs, we show that the spectral
distinguishability between the down-converted components is eliminated. This
scheme results in a visibility of 97.9+/-0.5% in the polarization basis without
any spectral filtering.Comment: 6 pages, 7 figure
Experimental many-pairs nonlocality
Collective measurements on large quantum systems together with a majority voting strategy can lead to a violation of the Clauser-Horne-Shimony-Holt Bell inequality. In the presence of many entangled pairs, this violation decreases quickly with the number of pairs and vanishes for some critical pair number that is a function of the noise present in the system. Here we show that a different binning strategy can lead to a more substantial Bell violation when the noise is sufficiently small. Given the relation between the critical pair number and the source noise, we then present an experiment where the critical pair number is used to quantify the quality of a high visibility photon pair source. Our results demonstrate nonlocal correlations using collective measurements operating on clusters of more than 40 photon pairs