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Martin Plávala
Universität Siegen, Germany, martin.plavala@uni-siegen.de
Contextuality as a precondition for entanglement
(joint work with Otfried Gühne)
contextuality vs causality
Quantum theory features several phenomena which can be considered as resources for information
processing tasks. Some of these effects, such as entanglement, arise in a non-local scenario, where
a quantum state is distributed between different parties. Other phenomena, such as contextuality,
can be observed if quantum states are prepared and then subsequently measured. There is a clear
distinction between non-local and sequential scenarios: Contextuality experiments have an explicit
causal structure since preparations precede measurements, while in the case of entanglement the
measurement events can be spacelike separated.
Here we provide an intimate connection between different resources by proving that
entanglement in a non-local scenario can only arise if there is preparation & measurement contextuality in
a sequential scenario derived from the non-local one by remote state preparation. Moreover, the
robust absence of entanglement implies the absence of contextuality. As a direct consequence, our
result allows to translate any inequality for testing preparation & measurement contextuality into
an entanglement test. In addition, entanglement witnesses can be used to obtain novel
noncontextuality inequalities which can be violated in the corresponding non-local experiment without any
causal structure.
