42,550 research outputs found
Device-independent dimension test in a multiparty Bell experiment
A device-independent dimension test for a Bell experiment aims to estimate
the underlying Hilbert space dimension that is required to produce given
measurement statistical data without any other assumptions concerning the
quantum apparatus. Previous work mostly deals with the two-party version of
this problem. In this paper, we propose a very general and robust approach to
test the dimension of any subsystem in a multiparty Bell experiment. Our
dimension test stems from the study of a new multiparty scenario which we call
prepare-and-distribute. This is like the prepare-and-measure scenario, but the
quantum state is sent to multiple, non-communicating parties. Through specific
examples, we show that our test results can be tight. Furthermore, we compare
the performance of our test to results based on known bipartite tests, and
witness remarkable advantage, which indicates that our test is of a true
multiparty nature. We conclude by pointing out that with some partial
information about the quantum states involved in the experiment, it is possible
to learn other interesting properties beyond dimension.Comment: 10 pages, 2 figure
Device-Independent Tests of Entropy
We show that the entropy of a message can be tested in a device-independent
way. Specifically, we consider a prepare-and-measure scenario with classical or
quantum communication, and develop two different methods for placing lower
bounds on the communication entropy, given observable data. The first method is
based on the framework of causal inference networks. The second technique,
based on convex optimization, shows that quantum communication provides an
advantage over classical, in the sense of requiring a lower entropy to
reproduce given data. These ideas may serve as a basis for novel applications
in device-independent quantum information processing
Sequential random access codes and self-testing of quantum measurement instruments
Quantum Random Access Codes (QRACs) are key tools for a variety of protocols
in quantum information theory. These are commonly studied in
prepare-and-measure scenarios in which a sender prepares states and a receiver
measures them. Here, we consider a three-party prepare-transform-measure
scenario in which the simplest QRAC is implemented twice in sequence based on
the same physical system. We derive optimal trade-off relations between the two
QRACs. We apply our results to construct semi-device independent self-tests of
quantum instruments, i.e. measurement channels with both a classical and
quantum output. Finally, we show how sequential QRACs enable inference of upper
and lower bounds on the sharpness parameter of a quantum instrument
A resource theory of quantum memories and their faithful verification with minimal assumptions
We provide a complete set of game-theoretic conditions equivalent to the
existence of a transformation from one quantum channel into another one, by
means of classically correlated pre/post processing maps only. Such conditions
naturally induce tests to certify that a quantum memory is capable of storing
quantum information, as opposed to memories that can be simulated by
measurement and state preparation (corresponding to entanglement-breaking
channels). These results are formulated as a resource theory of genuine quantum
memories (correlated in time), mirroring the resource theory of entanglement in
quantum states (correlated spatially). As the set of conditions is complete,
the corresponding tests are faithful, in the sense that any non
entanglement-breaking channel can be certified. Moreover, they only require the
assumption of trusted inputs, known to be unavoidable for quantum channel
verification. As such, the tests we propose are intrinsically different from
the usual process tomography, for which the probes of both the input and the
output of the channel must be trusted. An explicit construction is provided and
shown to be experimentally realizable, even in the presence of arbitrarily
strong losses in the memory or detectors.Comment: Addition of a quantitative study of memories as resources, and
reformulated part of the results in that ligh
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