12 research outputs found
Robustness of Device Independent Dimension Witnesses
Device independent dimension witnesses provide a lower bound on the
dimensionality of classical and quantum systems in a "black box" scenario where
only correlations between preparations, measurements and outcomes are
considered. We address the problem of the robustness of dimension witnesses,
namely that to witness the dimension of a system or to discriminate between its
quantum or classical nature, even in the presence of loss. We consider the case
when shared randomness is allowed between preparations and measurements and we
provide a threshold in the detection efficiency such that dimension witnessing
can still be performed.Comment: 8 pages, 5 figures, published versio
Quantum error correction with degenerate codes for correlated noise
We introduce a quantum packing bound on the minimal resources required by
nondegenerate error correction codes for any kind of noise. We prove that
degenerate codes can outperform nondegenerate ones in the presence of
correlated noise, by exhibiting examples where the quantum packing bound is
violated.Comment: 5 pages, published versio
Experimental implementation of unambiguous quantum reading
We provide the optimal strategy for unambiguous quantum reading of optical
memories, namely when perfect retrieving of information is achieved
probabilistically, for the case where noise and loss are negligible. We
describe the experimental quantum optical implementations, and provide
experimental results for the single photon case.Comment: 8 pages, 3 figures, 2 tables, added references, published versio
Communication capacity of mixed quantum t-designs
We operationally introduce mixed quantum t-designs as the most general
arbitrary-rank extension of projective quantum t-designs which preserves
indistinguishability from the uniform distribution for t copies. First, we
derive upper bounds on the classical communication capacity of any mixed
t-design measurement for t in [1,5]. Second, we explicitly compute the
classical communication capacity of several mixed t-design measurements,
including the depolarized version of any qubit and qutrit symmetric,
informationally complete (SIC) measurement and complete mutually unbiased
bases, the qubit icosahedral measurement, the Hoggar SIC measurement, any
anti-SIC (where each element is proportional to the projector on the subspace
orthogonal to one of the elements of the original SIC), and the uniform
distribution over pure effects.Comment: 9 pages, 3 figures, improved presentation, published versio
Detection loophole attacks on semi-device-independent quantum and classical protocols
Semi-device-independent quantum protocols realize information tasks – e.g. secure key
distribution, random access coding, and randomness generation – in a scenario where no
assumption on the internal working of the devices used in the protocol is made, except
their dimension. These protocols offer two main advantages: first, their implementation
is often less demanding than fully-device-independent protocols. Second, they are more
secure than their device-dependent counterparts. Their classical analogous is represented
by random access codes, which provide a general framework for describing one-sided classical
communication tasks. We discuss conditions under which detection inefficiencies can
be exploited by a malicious provider to fake the performance of semi-device-independent
quantum and classical protocols – and how to prevent it