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New Journal of Physics

Entanglement transmission through dense scattering medium

Peng Huang, Guihua Zeng

Published Mar 24, 2020• 4 citations
Publisher

Abstract

Abstract Scattering effects are ubiquitous in practical wireless optical links. Here a transmission model with complete consideration of scattered light and beam wandering effects for underwater link is developed, with the aim to completely characterize the received quantum state of light through dense scattering medium. Based on this model, we show the influence of scattered photons on the improvement of the entanglement after transmission through turbid water may vary for different copropagation scenarios, i.e., the contribution of scattered light on entanglement transmission may be turned from positive to negative, with increase of the strength of underwater beam wandering. And the attenuation coefficient and aperture size are found to be the dominant factors affecting the entanglement through underwater link. While for the counterpropagation scenario, the scattered photons will severely deteriorate the entanglement transmission especially for the high-loss scattering links. These findings may shed light on quantum entanglement transmission and help to develop its applications through dense scattering medium.

DOI
10.1088/1367-2630/ab82bc

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Abstract Scattering effects are ubiquitous in practical wireless optical links. Here a transmission model with complete consideration of scattered light and beam wandering effects for underwater link is developed, with the aim to completely characterize the received quantum state of light through dense scattering medium. Based on this model, we show the influence of scattered photons on the improvement of the entanglement after transmission through turbid water may vary for different copropagation scenarios, i.e., the contribution of scattered light on entanglement transmission may be turned from positive to negative, with increase of the strength of underwater beam wandering. And the attenuation coefficient and aperture size are found to be the dominant factors affecting the entanglement through underwater link. While for the counterpropagation scenario, the scattered photons will severely deteriorate the entanglement transmission especially for the high-loss scattering links. These findings may shed light on quantum entanglement transmission and help to develop its applications through dense scattering medium.
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This paper investigates an underwater quantum imaging algorithm assisted by autonomous underwater vehicles based on entangled photon pairs. The optical properties of water are first analyzed, and based on this analysis, the theoretical model for the backward scattering of water is derived. This paper consider the effects of underwater scattering, absorption and refraction on the quantum propagation characteristics. Under impacts of the undetwater light transmission characteristics, a theoretical model for underwater entangled photon quantum imaging is developed and the imaging reconstruction algorithm is derived. Moreover, this paper develop and analyze the signalto-noise ratio and visibility algorithms of underwater quantum imaging. This paper also completes the construction of an experimental optical path and conducts extensive experimental verification.
Abstract This work investigates physical-layer security of underwater wireless optical communication systems under covert non-line-of-sight (NLOS) eavesdropping caused by scattered photons. A first-order single-scattering model is developed for the near-transmitter NLOS eavesdropping link by incorporating seawater absorption, scattering, beam divergence, receiver field of view, and Eve’s geometry. Turbulence-induced fading on the legitimate line-of-sight link is also considered. Based on photon-counting detection, secrecy capacity, interception probability, and secrecy outage probability are analyzed. Results show that stronger scattering enlarges the high-risk region of NLOS information leakage, while stronger Bob-link turbulence degrades the secrecy performance of the system. A comparison with multiple-scattering Monte Carlo photon tracing for Jerlov IB and Jerlov II waters shows close agreement in the dominant spatial photon-count distribution.
Considering quantum signal transmission in the underwater links with scattering, we investigate the quantum channel model, the related capacity and secrecy performance. Monte Carlo simulation results demonstrate that the polarization angle change within [−20, 20] degrees accounts for 98%. We propose a quantum channel model for underwater link with scattering and theoretically investigate the capacity, where a larger proportion of scattered photons and a larger variation range of the polarization angle leads to lower quantum classical capacity. We analyze the secret key rate of BB84 protocol under unauthorized receiver attack (URA). The results show the maximum secure transmission distance under the given parameters of seawater decreases from 113 m to 58 m as the probability that the eavesdropper receives scattered photons increases from 0.1 % to 10%.
High-capacity, long-distance underwater optical communication enables a global scale optical network covering orbit, land, and water. Underwater communication using photons as carriers has a high channel capacity; however, the light scattering and absorption of water lead to an inevitable huge channel loss, setting an insurmountable transmission distance for existing underwater optical communication technologies. Here, we experimentally demonstrate the photon-inter-correlation optical communication (PICOC) in air–water scenarios. We retrieve additional internal correlation resources from the sparse single-photon stream with high fidelity. We successfully realize the 105-m-long underwater optical communication against a total loss up to 120.1 dB using only a microwatt laser. The demonstrated underwater light attenuation is equivalent to the loss of 883-m-long Jerlov type I water, encouraging the practical air–water optical communication to connect deeper underwater worlds.
Underwater quantum communication plays a crucial role in ensuring secure data transmission and extensible quantum networks in underwater environments. However, the implementation of such applications encounters challenges due to the light attenuation caused by the complicated natural seawater. This paper focuses on employing a model based on seawater chlorophyll-a concentration to characterize the absorption and scattering of light through quantum channels. We propose a multi-scattering random channel model, which demonstrates characteristics of the excess noise in different propagation directions of communication links. Furthermore, we consider the fidelity of a continuous-variable quantum teleportation through seawater channel. To enhance transmission performance, non-Gaussian operations have been conducted. Numerical simulations show that incorporating non-Gaussian operations enables the protocol to achieve higher fidelity transmission or lower fidelity fading rates over longer transmission distances.