979 research outputs found
Coexistence of continuous variable QKD with intense DWDM classical channels
We demonstrate experimentally the feasibility of continuous variable quantum
key distribution (CV-QKD) in dense-wavelength-division multiplexing networks
(DWDM), where QKD will typically have to coexist with several co- propagating
(forward or backward) C-band classical channels whose launch power is around
0dBm. We have conducted experimental tests of the coexistence of CV-QKD
multiplexed with an intense classical channel, for different input powers and
different DWDM wavelengths. Over a 25km fiber, a CV-QKD operated over the
1530.12nm channel can tolerate the noise arising from up to 11.5dBm classical
channel at 1550.12nm in forward direction (9.7dBm in backward). A positive key
rate (0.49kb/s) can be obtained at 75km with classical channel power of
respectively -3dBm and -9dBm in forward and backward. Based on these
measurements, we have also simulated the excess noise and optimized channel
allocation for the integration of CV-QKD in some access networks. We have, for
example, shown that CV-QKD could coexist with 5 pairs of channels (with nominal
input powers: 2dBm forward and 1dBm backward) over a 25km WDM-PON network. The
obtained results demonstrate the outstanding capacity of CV-QKD to coexist with
classical signals of realistic intensity in optical networks.Comment: 19 pages, 9 figures. Revised version, to appear in New Journal of
Physic
Experimental demonstration of Gaussian protocols for one-sided device-independent quantum key distribution
Nonlocal correlations, a longstanding foundational topic in quantum
information, have recently found application as a resource for cryptographic
tasks where not all devices are trusted, for example in settings with a highly
secure central hub, such as a bank or government department, and less secure
satellite stations which are inherently more vulnerable to hardware "hacking"
attacks. The asymmetric phenomena of Einstein-Podolsky-Rosen steering plays a
key role in one-sided device-independent quantum key distribution (1sDI-QKD)
protocols. In the context of continuous-variable (CV) QKD schemes utilizing
Gaussian states and measurements, we identify all protocols that can be 1sDI
and their maximum loss tolerance. Surprisingly, this includes a protocol that
uses only coherent states. We also establish a direct link between the relevant
EPR steering inequality and the secret key rate, further strengthening the
relationship between these asymmetric notions of nonlocality and device
independence. We experimentally implement both entanglement-based and
coherent-state protocols, and measure the correlations necessary for 1sDI key
distribution up to an applied loss equivalent to 7.5 km and 3.5 km of optical
fiber transmission respectively. We also engage in detailed modelling to
understand the limits of our current experiment and the potential for further
improvements. The new protocols we uncover apply the cheap and efficient
hardware of CVQKD systems in a significantly more secure setting.Comment: Addition of experimental results and (several) new author
Phase-noise limitations in continuous-variable quantum key distribution with homodyne detection
In continuous-variables quantum key distribution with coherent states, the advantage of performing the detection by using standard telecoms components is counterbalanced by the lack of a stable phase reference in homodyne detection due to the complexity of optical phase-locking circuits and to the unavoidable phase noise of lasers, which introduces a degradation on the achievable secure key rate. Pilot-assisted phase-noise estimation and postdetection compensation techniques are used to implement a protocol with coherent states where a local laser is employed and it is not locked to the received signal, but a postdetection phase correction is applied. Here the reduction of the secure key rate determined by the laser phase noise, for both individual and collective attacks, is analytically evaluated and a scheme of pilot-assisted phase estimation proposed, outlining the tradeoff in the system design between phase noise and spectral efficiency. The optimal modulation variance as a function of the phase-noise amount is derived
Experimental demonstration of long-distance continuous-variable quantum key distribution
Distributing secret keys with information-theoretic security is arguably one
of the most important achievements of the field of quantum information
processing and communications. The rapid progress in this field has enabled
quantum key distribution (QKD) in real-world conditions and commercial devices
are now readily available. QKD systems based on continuous variables present
the major advantage that they only require standard telecommunication
technology, and in particular, that they do not use photon counters. However,
these systems were considered up till now unsuitable for long-distance
communication. Here, we overcome all previous limitations and demonstrate for
the first time continuous-variable quantum key distribution over 80 km of
optical fibre. The demonstration includes all aspects of a practical scenario,
with real-time generation of secret keys, stable operation in a regular
environment, and use of finite-size data blocks for secret information
computation and key distillation. Our results correspond to an implementation
guaranteeing the strongest level of security for QKD reported to date for such
long distances and pave the way to practical applications of secure quantum
communications
Distributing Secret Keys with Quantum Continuous Variables: Principle, Security and Implementations
The ability to distribute secret keys between two parties with
information-theoretic security, that is, regardless of the capacities of a
malevolent eavesdropper, is one of the most celebrated results in the field of
quantum information processing and communication. Indeed, quantum key
distribution illustrates the power of encoding information on the quantum
properties of light and has far reaching implications in high-security
applications. Today, quantum key distribution systems operate in real-world
conditions and are commercially available. As with most quantum information
protocols, quantum key distribution was first designed for qubits, the
individual quanta of information. However, the use of quantum continuous
variables for this task presents important advantages with respect to qubit
based protocols, in particular from a practical point of view, since it allows
for simple implementations that require only standard telecommunication
technology. In this review article, we describe the principle of
continuous-variable quantum key distribution, focusing in particular on
protocols based on coherent states. We discuss the security of these protocols
and report on the state-of-the-art in experimental implementations, including
the issue of side-channel attacks. We conclude with promising perspectives in
this research field.Comment: 21 pages, 2 figures, 1 tabl
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