7,436 research outputs found
Large bipartite Bell violations with dichotomic measurements
In this paper we introduce a simple and natural bipartite Bell scenario, by
considering the correlations between two parties defined by general
measurements in one party and dichotomic ones in the other. We show that
unbounded Bell violations can be obtained in this context. Since such
violations cannot occur when both parties use dichotomic measurements, our
setting can be considered as the simplest one where this phenomenon can be
observed. Our example is essentially optimal in terms of the outputs and the
Hilbert space dimension
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
Classical and quantum partition bound and detector inefficiency
We study randomized and quantum efficiency lower bounds in communication
complexity. These arise from the study of zero-communication protocols in which
players are allowed to abort. Our scenario is inspired by the physics setup of
Bell experiments, where two players share a predefined entangled state but are
not allowed to communicate. Each is given a measurement as input, which they
perform on their share of the system. The outcomes of the measurements should
follow a distribution predicted by quantum mechanics; however, in practice, the
detectors may fail to produce an output in some of the runs. The efficiency of
the experiment is the probability that the experiment succeeds (neither of the
detectors fails).
When the players share a quantum state, this gives rise to a new bound on
quantum communication complexity (eff*) that subsumes the factorization norm.
When players share randomness instead of a quantum state, the efficiency bound
(eff), coincides with the partition bound of Jain and Klauck. This is one of
the strongest lower bounds known for randomized communication complexity, which
subsumes all the known combinatorial and algebraic methods including the
rectangle (corruption) bound, the factorization norm, and discrepancy.
The lower bound is formulated as a convex optimization problem. In practice,
the dual form is more feasible to use, and we show that it amounts to
constructing an explicit Bell inequality (for eff) or Tsirelson inequality (for
eff*). We give an example of a quantum distribution where the violation can be
exponentially bigger than the previously studied class of normalized Bell
inequalities.
For one-way communication, we show that the quantum one-way partition bound
is tight for classical communication with shared entanglement up to arbitrarily
small error.Comment: 21 pages, extended versio
Bell Violations through Independent Bases Games
In a recent paper, Junge and Palazuelos presented two two-player games
exhibiting interesting properties. In their first game, entangled players can
perform notably better than classical players. The quantitative gap between the
two cases is remarkably large, especially as a function of the number of inputs
to the players. In their second game, entangled players can perform notably
better than players that are restricted to using a maximally entangled state
(of arbitrary dimension). This was the first game exhibiting such a behavior.
The analysis of both games is heavily based on non-trivial results from Banach
space theory and operator space theory. Here we present two games exhibiting a
similar behavior, but with proofs that are arguably simpler, using elementary
probabilistic techniques and standard quantum information arguments. Our games
also give better quantitative bounds.Comment: Minor update
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