57,740 research outputs found
High-dimensional Bell test for a continuous variable state in phase space and its robustness to detection inefficiency
We propose a scheme for testing high-dimensional Bell inequalities in phase
space. High-dimensional Bell inequalities can be recast into the forms of a
phase-space version using quasiprobability functions with the complex-valued
order parameter. We investigate their violations for two-mode squeezed states
while increasing the dimension of measurement outcomes, and finally show the
robustness of high-dimensional tests to detection inefficiency.Comment: 8 pages, 2 figures; title and abstract changed, published versio
On Bell inequality violations with high-dimensional systems
Quantum correlations resulting in violations of Bell inequalities have
generated a lot of interest in quantum information science and fundamental
physics. In this paper, we address some questions that become relevant in
Bell-type tests involving systems with local dimension greater than 2. For
CHSH-Bell tests within 2-dimensional subspaces of such high-dimensional
systems, it has been suggested that experimental violation of Tsirelson's bound
indicates that more than 2-dimensional entanglement was present. We explain
that the overstepping of Tsirelson's bound is due to violation of fair
sampling, and can in general be reproduced by a separable state, if fair
sampling is violated. For a class of Bell-type inequalities generalized to
d-dimensional systems, we then consider what level of violation is required to
guarantee d-dimensional entanglement of the tested state, when fair sampling is
satisfied. We find that this can be used as an experimentally feasible test of
d-dimensional entanglement for up to quite high values of d
Experimental test of high-dimensional quantum contextuality based on contextuality concentration
Contextuality is a distinctive feature of quantum theory and a fundamental
resource for quantum computation. However, existing examples of contextuality
in high-dimensional systems lack the necessary robustness required in
experiments. Here we address this problem by identifying a family of
noncontextuality inequalities whose maximum quantum violation grows with the
dimension of the system. At first glance, this contextuality is the
single-system version of an extreme form of multipartite Bell nonlocality. What
is interesting is that the single-system version achieves the same degree of
contextuality but using a Hilbert space of {\em lower} dimension. That is,
contextualize "concentrates" as the degree of contextuality per dimension
increases. We demonstrate the usefulness of this result by showing the
experimental observation of contextuality in a single system of dimension
seven. By simulating sequences of quantum ideal measurements in an all-optical
setup using projective measurements on structured light, we report a violation
of 68.7 standard deviations of the simplest of the noncontextuality
inequalities identified. Our results advance the investigation of
high-dimensional contextuality, its connection to the Clifford algebra, and its
role in quantum computation.Comment: 7+5 pages, 4+2 figures. Comments are welcom
Demonstrating multilevel entanglement and optimal quantum measurements
Optimal generalised quantum measurements are important for quantum information applications
in both photonic and solid state systems. However, until now, the implementations
of such measurements have been optical. Entanglement is also a very important
resource in quantum communication and information processing. However, highdimensional
entangled states and corresponding Bell-inequality violations are challenging
to detect and demonstrate experimentally. This thesis focuses on these two aspects of
signal detection.
A cavity quantum electrodynamics (QED) scheme to realise an optimised quantum
measurement demonstrating the superadditivity of quantum channel capacity is proposed
and analysed. The measurement is shown to be feasible using atoms in a cavity QED setup
even in the presence of rather high levels of experimental errors. This is interesting because
cavity QED realisations could potentially be more easily scaled to increase quantum
coding gain. Experimental unambiguous discrimination between non-orthogonal states is
also carried out for the first time in the solid state using the nuclear spin of a nitrogen
atom associated with a defect in bulk diamond—an important step for implementations
of solid-state quantum computing.
This thesis presents a method for verifying entanglement dimension using only Bell
inequality test measurements. It also shows experimental results demonstrating genuine
eleven-dimensional two-photon orbital angular momentum (OAM) entanglement and violations
of generalised Bell inequalities up to dimension twelve. The demonstrated highdimensional
entanglement is potentially useful for closing the detection loophole in Belltest
experiments and for real-world large-alphabet quantum-cryptography applications
Multidimensional quantum entanglement with large-scale integrated optics
The ability to control multidimensional quantum systems is key for the
investigation of fundamental science and for the development of advanced
quantum technologies. Here we demonstrate a multidimensional integrated quantum
photonic platform able to robustly generate, control and analyze
high-dimensional entanglement. We realize a programmable bipartite entangled
system with dimension up to on a large-scale silicon-photonics
quantum circuit. The device integrates more than 550 photonic components on a
single chip, including 16 identical photon-pair sources. We verify the high
precision, generality and controllability of our multidimensional technology,
and further exploit these abilities to demonstrate key quantum applications
experimentally unexplored before, such as quantum randomness expansion and
self-testing on multidimensional states. Our work provides a prominent
experimental platform for the development of multidimensional quantum
technologies.Comment: Science, (2018
Bell inequalities for three systems and arbitrarily many measurement outcomes
We present a family of Bell inequalities for three parties and arbitrarily
many outcomes, which can be seen as a natural generalization of the Mermin Bell
inequality. For a small number of outcomes, we verify that our inequalities
define facets of the polytope of local correlations. We investigate the quantum
violations of these inequalities, in particular with respect to the Hilbert
space dimension. We provide strong evidence that the maximal quantum violation
can only be reached using systems with local Hilbert space dimension exceeding
the number of measurement outcomes. This suggests that our inequalities can be
used as multipartite dimension witnesses.Comment: v1 6 pages, 4 tables; v2 Published version with minor typos correcte
A Zoology of Bell inequalities resistant to detector inefficiency
We derive both numerically and analytically Bell inequalities and quantum
measurements that present enhanced resistance to detector inefficiency. In
particular we describe several Bell inequalities which appear to be optimal
with respect to inefficient detectors for small dimensionality d=2,3,4 and 2 or
more measurement settings at each side. We also generalize the family of Bell
inequalities described in Collins et all (Phys. Rev. Lett. 88, 040404) to take
into account the inefficiency of detectors. In addition we consider the
possibility for pairs of entangled particles to be produced with probability
less than one. We show that when the pair production probability is small, one
must in general use different Bell inequalities than when the pair production
probability is high.Comment: 12 pages, revtex. Appendix completed, minor revision
- …