23 research outputs found
Layered Quantum Key Distribution
We introduce a family of QKD protocols for distributing shared random keys
within a network of users. The advantage of these protocols is that any
possible key structure needed within the network, including broadcast keys
shared among subsets of users, can be implemented by using a particular
multi-partite high-dimensional quantum state. This approach is more efficient
in the number of quantum channel uses than conventional quantum key
distribution using bipartite links. Additionally, multi-partite
high-dimensional quantum states are becoming readily available in quantum
photonic labs, making the proposed protocols implementable using current
technology.Comment: 11 pages, 5 figures. In version 2 we extended section 4 about the
dimension-rate trade-off and corrected minor error
Device-independent randomness extraction for arbitrarily weak min-entropy source
Expansion and amplification of weak randomness plays a crucial role in many
security protocols. Using quantum devices, such procedure is possible even
without trusting the devices used, by utilizing correlations between outcomes
of parts of the devices. We show here how to extract random bits with an
arbitrarily low bias from a single arbitrarily weak min-entropy source in a
device independent setting. To do this we use Mermin devices that exhibit
super-classical correlations. Number of devices used scales polynomially in the
length of the random sequence . Our protocol is robust, it can tolerate
devices that malfunction with a probability dropping polynomially in at the
cost of a minor increase of the number of devices used.Comment: 5 pages + 3 pages supplementary materia
Weak randomness completely trounces the security of QKD
In usual security proofs of quantum protocols the adversary (Eve) is expected
to have full control over any quantum communication between any communicating
parties (Alice and Bob). Eve is also expected to have full access to an
authenticated classical channel between Alice and Bob. Unconditional security
against any attack by Eve can be proved even in the realistic setting of device
and channel imperfection. In this Letter we show that the security of QKD
protocols is ruined if one allows Eve to possess a very limited access to the
random sources used by Alice. Such knowledge should always be expected in
realistic experimental conditions via different side channels
High-Dimensional Pixel Entanglement: Efficient Generation and Certification
Photons offer the potential to carry large amounts of information in their
spectral, spatial, and polarisation degrees of freedom. While state-of-the-art
classical communication systems routinely aim to maximize this
information-carrying capacity via wavelength and spatial-mode division
multiplexing, quantum systems based on multi-mode entanglement usually suffer
from low state quality, long measurement times, and limited encoding capacity.
At the same time, entanglement certification methods often rely on assumptions
that compromise security. Here we show the certification of photonic
high-dimensional entanglement in the transverse position-momentum
degree-of-freedom with a record quality, measurement speed, and entanglement
dimensionality, without making any assumptions about the state or channels.
Using a tailored macro-pixel basis, precise spatial-mode measurements, and a
modified entanglement witness, we demonstrate state fidelities of up to 94.4%
in a 19-dimensional state-space, entanglement in up to 55 local dimensions, and
an entanglement-of-formation of up to 4 ebits. Furthermore, our measurement
times show an improvement of more than two orders of magnitude over previous
state-of-the-art demonstrations. Our results pave the way for noise-robust
quantum networks that saturate the information-carrying capacity of single
photons