  Entanglement sources that produce many entangled states act as a main
component in applications exploiting quantum physics such as quantum
communication and cryptography. Realistic sources are inherently noisy, cannot
run for an infinitely long time, and do not necessarily behave in an
independent and identically distributed manner. An important question then
arises -- how can one test, or certify, that a realistic source produces high
amounts of entanglement? Crucially, a meaningful and operational solution
should allow us to certify the entanglement which is available for further
applications after performing the test itself (in contrast to assuming the
availability of an additional source which can produce more entangled states,
identical to those which were tested). To answer the above question and lower
bound the amount of entanglement produced by an uncharacterised source, we
present a protocol that can be run by interacting classically with
uncharacterised (but not entangled to one another) measurement devices used to
measure the states produced by the source. A successful run of the protocol
implies that the remaining quantum state has high amounts of one-shot
distillable entanglement. That is, one can distill many maximally entangled
states out of the single remaining state. Importantly, our protocol can
tolerate noise and, thus, certify entanglement produced by realistic sources.
With the above properties, the protocol acts as the first "operational
device-independent entanglement certification protocol" and allows one to test
and benchmark uncharacterised entanglement sources which may be otherwise
incomparable.
