1,680 research outputs found
Bell Inequality Tests with Macroscopic Entangled States of Light
Quantum correlations may violate the Bell inequalities. Most of the
experimental schemes confirming this prediction have been realized in
all-optical Bell tests suffering from the detection loophole. Experiment which
closes this loophole and the locality loophole simultaneously is highly
desirable and remains challenging. A novel approach to a loophole-free Bell
tests is based on amplification of the entangled photons, i.e.\@ on macroscopic
entanglement, which optical signal should be easy to detect. However, the
macroscopic states are partially indistinguishable by the classical detectors.
An interesting idea to overcome these limitations is to replace the
postselection by an appropriate preselection immediately after the
amplification. This is in the spirit of state preprocessing revealing hidden
nonlocality. Here, we examine one of possible preselections, but the presented
tools can be used for analysis of other schemes. Filtering methods making the
macroscopic entanglement useful for Bell test and quantum protocols are the
subject of an intensive study in the field nowadays.Comment: 4 page
Using macroscopic entanglement to close the detection loophole in Bell inequality
We consider a Bell-like inequality performed using various instances of
multi-photon entangled states to demonstrate that losses occurring after the
unitary transformations used in the nonlocality test can be counteracted by
enhancing the "size" of such entangled states. In turn, this feature can be
used to overcome detection inefficiencies affecting the test itself: a slight
increase in the size of such states, pushing them towards a more "macroscopic"
form of entanglement, significantly improves the state robustness against
detection inefficiency, thus easing the closing of the detection loophole.
Differently, losses before the unitary transformations cause decoherence
effects that cannot be compensated using macroscroscopic entanglement.Comment: 5 pages, 5 figures, to be published in Phys. Rev.
Loss-tolerant hybrid measurement test of CHSH inequality with weakly amplified N00N states
Although our understanding of Bell's theorem and experimental techniques to
test it have improved over the last 40 years, thus far all Bell tests have
suffered at least from the detection or the locality loophole. Most photonic
Bell tests rely on inefficient discrete-outcome measurements, often provided by
photon counting detection. One possible way to close the detection loophole in
photonic Bell tests is to involve efficient continuous-variable measurements
instead, such as homodyne detection. Here, we propose a test of the
Clauser-Horne-Shimony-Holt (CHSH) inequality that applies photon counting and
homodyne detection on weakly amplified two-photon N00N states. The scheme
suggested is remarkably robust against experimental imperfections and suits the
limits of current technology. As amplified quantum states are considered, our
work also contributes to the exploration of entangled macroscopic quantum
systems. Further, it may constitute an alternative platform for a loophole-free
Bell test, which is also important for quantum-technological applications.Comment: 9 pages, 3 figure
Shifting the Quantum-Classical Boundary: Theory and Experiment for Statistically Classical Optical Fields
The growing recognition that entanglement is not exclusively a quantum
property, and does not even originate with Schr\"odinger's famous remark about
it [Proc. Camb. Phil. Soc. 31, 555 (1935)], prompts examination of its role in
marking the quantum-classical boundary. We have done this by subjecting
correlations of classical optical fields to new Bell-analysis experiments, and
report here values of the Bell parameter greater than . This
is many standard deviations outside the limit established by the
Clauser-Horne-Shimony-Holt (CHSH) Bell inequality [Phys. Rev. Lett. 23, 880
(1969)], in agreement with our theoretical classical prediction, and not far
from the Tsirelson limit . These results cast a new light
on the standard quantum-classical boundary description, and suggest a
reinterpretation of it.Comment: Comments and Remarks are warmly welcome! arXiv admin note: text
overlap with arXiv:1406.333
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