Quantum Turbulence: Achievements and Challenges

Ivan B. Djordjević

In our recent paper, we proposed using the atmospheric turbulent channel as a source of randomness to simultaneously address various challenges in physical-layer security (PLS), quantum key distribution (QKD), and post-quantum cryptography (PQC). However, the long coherence time of atmospheric turbulence channels limits the achievable secret-key rates (SKRs). To address this issue, we initially leveraged the turbulence effects only during the system’s initialization phase. In this paper, we present a source-based secret key generation scheme that overcomes the limitations imposed by the long coherence time of the turbulent channel, without requiring initialization. The scheme utilizes both atmospheric turbulence and background radiation as sources of randomness. It offers security superior to PQC and is comparable to QKD, while enabling significantly higher SKRs, making it fully compatible with state-of-the-art optical communications.

Kyle Thompson

Carlo F. Barenghi, Ladislav Skrbek, Katepalli R. Sreenivasan

Langer, Stefan, Stefan Görtz

Accurately simulating turbulent, compressible fluids remains a major computational challenge for the aviation industry and a key to achieving future climate goals. Despite advances in computational fluid dynamics (CFD), limitations in turbulence models and the immense cost of high-fidelity simulations make scale-resolving full-aircraft simulations unrealistic. Quantum computing could overcome these barriers, as even few qubits can represent vast degrees of freedom. However, due to numerous obstacles such as the restriction to unitary operators, the read-out problem, and the limited availability of actual quantum hardware, the development of efficient algorithms for solving fluid mechanics equations is a real scientific challenge. This presentation highlights current efforts within the DLR QCI project ToQuaFlics to explore the potential of quantum computing for aerodynamic simulations.

Masoud Ghalaii, Stefano Pirandola

Abstract Since the invention of the laser in the 60s, one of the most fundamental communication channels has been the free-space optical channel. For this type of channel, a number of effects generally need to be considered, including diffraction, refraction, atmospheric extinction, pointing errors and, most importantly, turbulence. Because of all these adverse features, the free-space channel is more difficult to study than a stable fiber-based link. For the same reasons, only recently it has been possible to establish the ultimate performances achievable in quantum communications via free-space channels. Differently from previous literature, mainly focused on the regime of weak turbulence, this work considers the free-space optical channel in the more challenging regime of moderate-to-strong turbulence. This regime may occur in long-distance free-space links on the ground, in uplink to high-altitude platform systems (HAPS) and, more interestingly, in downlink from near-horizon satellites. In such a regime we rigorously investigate ultimate limits for quantum communications and show that composable keys can be extracted using continuous variable quantum key distribution. In particular, we apply our results to downlink from satellites at large zenith angles, for which not only turbulence is strong but also refraction causes non-trivial effects in terms of trajectory elongation.

William Frank Vinen