1,460 research outputs found
Realigned Hardy's Paradox
Hardy's paradox provides an all-versus-nothing fashion to directly certify
that quantum mechanics cannot be completely described by local realistic
theory. However, when considering potential imperfections in experiments, like
imperfect entanglement source and low detection efficiency, the original
Hardy's paradox may induce a rather small Hardy violation and only be realized
by expensive quantum systems. To overcome this problem, we propose a realigned
Hardy's paradox. Compared with the original version of Hardy's paradox, the
realigned Hardy's paradox can dramatically improve the Hardy violation. Then,
we generalize the realigned Hardy's paradox to arbitrary even dichotomic
measurements. For and cases, the realigned Hardy's paradox can
achieve Hardy values approximate and
respectively compared with of the original Hardy's paradox. Meanwhile,
the structure of the realigned Hardy's paradox is simpler and more robust in
the sense that there is only one Hardy condition rather than three conditions.
One can anticipate that the realigned Hardy's paradox can tolerate more
experimental imperfections and stimulate more fascinating quantum information
applications.Comment: 7 pages, 1 figur
Field demonstration of distributed quantum sensing without post-selection
Distributed quantum sensing can provide quantum-enhanced sensitivity beyond
the shot-noise limit (SNL) for sensing spatially distributed parameters. To
date, distributed quantum sensing experiments have been mostly accomplished in
laboratory environments without a real space separation for the sensors. In
addition, the post-selection is normally assumed to demonstrate the sensitivity
advantage over the SNL. Here, we demonstrate distributed quantum sensing in
field and show the unconditional violation (without post-selection) of SNL up
to 0.916 dB for the field distance of 240 m. The achievement is based on a
loophole free Bell test setup with entangled photon pairs at the averaged
heralding efficiency of 73.88%. Moreover, to test quantum sensing in real life,
we demonstrate the experiment for long distances (with 10-km fiber) together
with the sensing of a completely random and unknown parameter. The results
represent an important step towards a practical quantum sensing network for
widespread applications.Comment: 8 pages, 5 figure
Device-independent randomness expansion against quantum side information
The ability to produce random numbers that are unknown to any outside party
is crucial for many applications. Device-independent randomness generation does
not require trusted devices and therefore provides strong guarantees of the
security of the output, but it comes at the price of requiring the violation of
a Bell inequality for implementation. A further challenge is to make the bounds
in the security proofs tight enough to allow randomness expansion with
contemporary technology. Although randomness has been generated in recent
experiments, the amount of randomness consumed in doing so has been too high to
certify expansion based on existing theory. Here we present an experiment that
demonstrates device-independent randomness expansion. By developing a Bell test
setup with a single-photon detection efficiency of around and by using a
spot-checking protocol, we achieve a net gain of certified
bits with a soundness error . The experiment ran for
h, which corresponds to an average rate of randomness generation of
bits per second. By developing the entropy accumulation theorem, we establish
security against quantum adversaries. We anticipate that this work will lead to
further improvements that push device-independence towards commercial
viability.Comment: v2: Update to match published version. Small error in the
term in Theorem 3 in the published supplementary information corrected her
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