42 research outputs found
Realistic noise-tolerant randomness amplification using finite number of devices
Randomness is a fundamental concept, with implications from security of modern data systems, to fundamental laws of nature and even the philosophy of science. Randomness is called certified if it describes events that cannot be pre-determined by an external adversary. It is known that weak certified randomness can be amplified to nearly ideal randomness using quantum-mechanical systems. However, so far, it was unclear whether randomness amplification is a realistic task, as the existing proposals either do not tolerate noise or require an unbounded number of different devices. Here we provide an error-tolerant protocol using a finite number of devices for amplifying arbitrary weak randomness into nearly perfect random bits, which are secure against a no-signalling adversary. The correctness of the protocol is assessed by violating a Bell inequality, with the degree of violation determining the noise tolerance threshold. An experimental realization of the protocol is within reach of current technology
Source-independent quantum random number generation
Quantum random number generators can provide genuine randomness by appealing
to the fundamental principles of quantum mechanics. In general, a physical
generator contains two parts---a randomness source and its readout. The source
is essential to the quality of the resulting random numbers; hence, it needs to
be carefully calibrated and modeled to achieve information-theoretical provable
randomness. However, in practice, the source is a complicated physical system,
such as a light source or an atomic ensemble, and any deviations in the
real-life implementation from the theoretical model may affect the randomness
of the output. To close this gap, we propose a source-independent scheme for
quantum random number generation in which output randomness can be certified,
even when the source is uncharacterized and untrusted. In our randomness
analysis, we make no assumptions about the dimension of the source. For
instance, multiphoton emissions are allowed in optical implementations. Our
analysis takes into account the finite-key effect with the composable security
definition. In the limit of large data size, the length of the input random
seed is exponentially small compared to that of the output random bit. In
addition, by modifying a quantum key distribution system, we experimentally
demonstrate our scheme and achieve a randomness generation rate of over
bit/s.Comment: 11 pages, 7 figure
All Pure Bipartite Entangled States can be Self-Tested
Device-independent self-testing allows to uniquely characterize the quantum
state shared by untrusted parties (up to local isometries) by simply inspecting
their correlations, and requiring only minimal assumptions, namely a
no-signaling constraint on the untrusted parties and the validity of quantum
mechanics. The device-independent approach exploits the fact that certain
non-local correlations can be uniquely achieved by measurements on a particular
quantum state. We can think of these correlations as a "classical fingerprint"
of the self-tested quantum state. In this work, we answer affirmatively the
outstanding open question of whether all pure bipartite entangled states can be
self-tested, by providing explicit self-testing correlations for each.Comment: 16 pages. Added self-testing of measurements, corrected typos, and
improved expositio
Quantum violations in the Instrumental scenario and their relations to the Bell scenario
The causal structure of any experiment implies restrictions on the observable
correlations between measurement outcomes, which are different for experiments
exploiting classical, quantum, or post-quantum resources. In the study of Bell
nonlocality, these differences have been explored in great detail for more and
more involved causal structures. Here, we go in the opposite direction and
identify the simplest causal structure which exhibits a separation between
classical, quantum, and post-quantum correlations. It arises in the so-called
Instrumental scenario, known from classical causal models. We derive
inequalities for this scenario and show that they are closely related to
well-known Bell inequalities, such as the Clauser-Horne-Shimony-Holt
inequality, which enables us to easily identify their classical, quantum, and
post-quantum bounds as well as strategies violating the first two. The
relations that we uncover imply that the quantum or post-quantum advantages
witnessed by the violation of our Instrumental inequalities are not
fundamentally different from those witnessed by the violations of standard
inequalities in the usual Bell scenario. However, non-classical tests in the
Instrumental scenario require fewer input choices than their Bell scenario
counterpart, which may have potential implications for device-independent
protocols.Comment: 12 pages, 3 figures. Comments welcome! v4: published version in
Quantum journa