768 research outputs found
Demonstration of Einstein-Podolsky-Rosen Steering with Enhanced Subchannel Discrimination
Einstein-Podolsky-Rosen (EPR) steering describes a quantum nonlocal
phenomenon in which one party can nonlocally affect the other's state through
local measurements. It reveals an additional concept of quantum nonlocality,
which stands between quantum entanglement and Bell nonlocality. Recently, a
quantum information task named as subchannel discrimination (SD) provides a
necessary and sufficient characterization of EPR steering. The success
probability of SD using steerable states is higher than using any unsteerable
states, even when they are entangled. However, the detailed construction of
such subchannels and the experimental realization of the corresponding task are
still technologically challenging. In this work, we designed a feasible
collection of subchannels for a quantum channel and experimentally demonstrated
the corresponding SD task where the probabilities of correct discrimination are
clearly enhanced by exploiting steerable states. Our results provide a concrete
example to operationally demonstrate EPR steering and shine a new light on the
potential application of EPR steering.Comment: 16 pages, 8 figures, appendix include
Beyond Gisin's Theorem and its Applications: Violation of Local Realism by Two-Party Einstein-Podolsky-Rosen Steering
We demonstrate here that for a given mixed multi-qubit state if there are at
least two observers for whom mutual Einstein-Podolsky-Rosen steering is
possible, i.e. each observer is able to steer the other qubits into two
different pure states by spontaneous collapses due to von Neumann type
measurements on his/her qubit, then nonexistence of local realistic models is
fully equivalent to quantum entanglement (this is not so without this
condition). This result leads to an enhanced version of Gisin's theorem
(originally: all pure entangled states violate local realism). Local realism is
violated by all mixed states with the above steering property. The new class of
states allows one e.g. to perform three party secret sharing with just pairs of
entangled qubits, instead of three qubit entanglements (which are currently
available with low fidelity). This significantly increases the feasibility of
having high performance versions of such protocols. Finally, we discuss some
possible applications.Comment: 9 pages, 1 figur
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