2,457 research outputs found
CV-QKD with Gaussian and non-Gaussian Entangled States over Satellite-based Channels
In this work we investigate the effectiveness of continuous-variable (CV)
entangled states, transferred through high-loss atmospheric channels, as a
means of viable quantum key distribution (QKD) between terrestrial stations and
low-Earth orbit (LEO) satellites. In particular, we investigate the role played
by the Gaussian CV states as compared to non-Gaussian states. We find that
beam-wandering induced atmospheric losses lead to QKD performance levels that
are in general quite different from those found in fixed-attenuation channels.
For example, circumstances can be found where no QKD is viable at some fixed
loss in fiber but is viable at the same mean loss in fading channels. We also
find that, in some circumstances, the QKD relative performance of Gaussian and
non-Gaussian states can in atmospheric channels be the reverse of that found in
fixed-attenuation channels. These findings show that the nature of the
atmospheric channel can have a large impact on the QKD performance. Our results
should prove useful for emerging global quantum communications that use LEO
satellites as communication relays.Comment: 7 pages, 5 figure
Gaussian Entanglement Distribution via Satellite
In this work we analyse three quantum communication schemes for the
generation of Gaussian entanglement between two ground stations. Communication
occurs via a satellite over two independent atmospheric fading channels
dominated by turbulence-induced beam wander. In our first scheme the
engineering complexity remains largely on the ground transceivers, with the
satellite acting simply as a reflector. Although the channel state information
of the two atmospheric channels remains unknown in this scheme, the Gaussian
entanglement generation between the ground stations can still be determined. On
the ground, distillation and Gaussification procedures can be applied, leading
to a refined Gaussian entanglement generation rate between the ground stations.
We compare the rates produced by this first scheme with two competing schemes
in which quantum complexity is added to the satellite, thereby illustrating the
trade-off between space-based engineering complexity and the rate of
ground-station entanglement generation.Comment: Closer to published version (to appear in Phys. Rev. A) 13 pages, 6
figure
Photonic Engineering for CV-QKD over Earth-Satellite Channels
Quantum Key Distribution (QKD) via satellite offers up the possibility of
unconditionally secure communications on a global scale. Increasing the secret
key rate in such systems, via photonic engineering at the source, is a topic of
much ongoing research. In this work we investigate the use of photon-added
states and photon-subtracted states, derived from two mode squeezed vacuum
states, as examples of such photonic engineering. Specifically, we determine
which engineered-photonic state provides for better QKD performance when
implemented over channels connecting terrestrial receivers with Low-Earth-Orbit
satellites. We quantify the impact the number of photons that are added or
subtracted has, and highlight the role played by the adopted model for
atmospheric turbulence and loss on the predicted key rates. Our results are
presented in terms of the complexity of deployment used, with the simplest
deployments ignoring any estimate of the channel, and the more sophisticated
deployments involving a feedback loop that is used to optimize the key rate for
each channel estimation. The optimal quantum state is identified for each
deployment scenario investigated.Comment: Updated reference lis
Atmospheric continuous-variable quantum communication
We present a quantum communication experiment conducted over a point-to-point
free-space link of 1.6 km in urban conditions. We study atmospheric influences
on the capability of the link to act as a continuous-variable (CV) quantum
channel. Continuous polarization states (that contain the signal encoding as
well as a local oscillator in the same spatial mode) are prepared and sent over
the link in a polarization multiplexed setting. Both signal and local
oscillator undergo the same atmospheric fluctuations. These are intrinsically
auto-compensated which removes detrimental influences on the interferometric
visibility. At the receiver, we measure the Q-function and interpret the data
using the framework of effective entanglement. We compare different state
amplitudes and alphabets (two-state and four-state) and determine their optimal
working points with respect to the distributed effective entanglement. Based on
the high entanglement transmission rates achieved, our system indicates the
high potential of atmospheric links in the field of CV QKD.Comment: 13 pages, 7 figure
Quantum Entanglement Distribution in Next-Generation Wireless Communication Systems
In this work we analyze the distribution of quantum entanglement over
communication channels in the millimeter-wave regime. The motivation for such a
study is the possibility for next-generation wireless networks (beyond 5G) to
accommodate such a distribution directly - without the need to integrate
additional optical communication hardware into the transceivers. Future
wireless communication systems are bound to require some level of quantum
communications capability. We find that direct quantum-entanglement
distribution in the millimeter-wave regime is indeed possible, but that its
implementation will be very demanding from both a system-design perspective and
a channel-requirement perspective.Comment: 6 pages, 4 figure
Atmospheric channel effects on terrestrial free space optical communication links
Abstract. This paper illustrates the challenges imposed by the atmospheric channel on the design of a terrestrial laser communication link. The power loss due to scattering effect is described using the Kim/Kruse scattering model while the effect and the penalty imposed by atmospheric turbulence is highlighted by considering the bit error rate (BER) of an On-Off Keying modulated link in an optical Poisson channel. The power loss due to thick fog can measure over 100 dB/km while snow and rain result in much lower attenuation. We show that non-uniformity in the atmospheric temperature also contributes to performance deterioration due to scintillation effect. At a BER of 10-4, for a channel with a turbulence strength of>0.1, the penalty imposed by turbulence induced fading is over 20 photoelectron counts in order to achieve the same level of performance as a channel with no fading. The work reported here is part of the EU COST actions and EU projects.
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