13 research outputs found
A Novel Bulk-Optics Scheme for Quantum Walk with High Phase Stability
A novel bulk optics scheme for quantum walks is presented. It consists of a
one-dimensional lattice built on two concatenated displaced Sagnac
interferometers that make it possible to reproduce all the possible
trajectories of an optical quantum walk. Because of the closed loop
configuration, the interferometric structure is intrinsically stable in phase.
Moreover, the lattice structure is highly configurable, as any phase component
perceived by the walker is accessible, and finally, all output modes can be
measured at any step of the quantum walk evolution. We report here on the
experimental implementation of ordered and disordered quantum walks.Comment: This manuscript is organized in 5 sections, containing 8 pages and 7
figure
Phase Noise in Real-World Twin-Field Quantum Key Distribution
We investigate the impact of noise sources in real-world implementations of
Twin-Field Quantum Key Distribution (TF-QKD) protocols, focusing on phase noise
from photon sources and connecting fibers. Our work emphasizes the role of
laser quality, network topology, fiber length, arm balance, and detector
performance in determining key rates. Remarkably, it reveals that the leading
TF-QKD protocols are similarly affected by phase noise despite different
mechanisms. Our study demonstrates duty cycle improvements of over 2x through
narrow-linewidth lasers and phase-control techniques, highlighting the
potential synergy with high-precision time/frequency distribution services.
Ultrastable lasers, evolving toward integration and miniaturization, offer
promise for agile TF-QKD implementations on existing networks. Properly
addressing phase noise and practical constraints allows for consistent key rate
predictions, protocol selection, and layout design, crucial for establishing
secure long-haul links for the Quantum Communication Infrastructures under
development in several countries.Comment: 18 pages, 8 figures, 2 table
Realistic Threat Models for Satellite-Based Quantum Key Distribution
The security of prepare-and-measure satellite-based quantum key distribution
(QKD), under restricted eavesdropping scenarios, is addressed. We particularly
consider cases where the eavesdropper, Eve, has limited access to the
transmitted signal by Alice, and/or Bob's receiver station. This restriction is
modeled by lossy channels between Alice/Bob and Eve, where the transmissivity
of such channels can, in principle, be bounded by monitoring techniques. An
artefact of such lossy channels is the possibility of having bypass channels,
those which are not accessible to Eve, but may not necessarily be characterized
by the users either. This creates interesting, {\it unexplored}, scenarios for
analyzing QKD security. In this paper, we obtain generic bounds on the key rate
in the presence of bypass channels and apply them to continuous-variable QKD
protocols with Gaussian encoding with direct and reverse reconciliation. We
find regimes of operation in which the above restrictions on Eve can
considerably improve system performance. We also develop customised bounds for
several protocols in the BB84 family and show that, in certain regimes, even
the simple protocol of BB84 with weak coherent pulses is able to offer positive
key rates at high channel losses, which would otherwise be impossible under an
unrestricted Eve. In this case the limitation on Eve would allow Alice to send
signals with larger intensities than the optimal value under an ideal Eve,
which effectively reduces the effective channel loss. In all these cases, the
part of the transmitted signal that does not reach Eve can play a non-trivial
role in specifying the achievable key rate. Our work opens up new security
frameworks for spaceborne quantum communications systems.Comment: 39 pages, 17 figure
Stroboscopie evolutions of quantum states and quantum walks in a double-Sagnac interferometric configuration
The study of the evolution of quantum states performed with photonic techniques, commonly requires the use of complex interferometric schemes. Here we present a novel setup based on multipass bulk interference that allows to recreate and measure different kinds of quantum state evolutions, passing from sequential maps to quantum walks
A Novel Bulk-Optics Scheme for Quantum Walk with High Phase Stability
A novel bulk optics scheme for quantum walks is presented. It consists of a one-dimensional lattice built on two concatenated displaced Sagnac interferometers that make it possible to reproduce all the possible trajectories of an optical quantum walk. Because of the closed loop configuration, the interferometric structure is intrinsically stable in phase. Moreover, the lattice structure is highly configurable, as any phase component perceived by the walker is accessible, and finally, all output modes can be measured at any step of the quantum walk evolution. We report here on the experimental implementation of ordered and disordered quantum walks