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Optical and Quantum Sensing and Precision Metrology II

Transmission of hidden images within noise

Steven D. Johnson, Alex R. McMillan, Stefan Frick, John Rarity, Miles J. Padgett

Published Mar 13, 2024• 0 citations
Publisher

Abstract

The secure transmission of an image can be accomplished by encoding the image information, securely communicating this information, and subsequently reconstructing the image. As an alternative, here we show how the image itself can be directly transmitted while ensuring that the presence of any eavesdropper is revealed in a way akin to quantum key distribution. We achieve this transmission using a photon-pair source with the deliberate addition of a thermal light source as background noise. One photon of the pair illuminates the object, which is masked from an eavesdropper by adding indistinguishable thermal photons, the other photon of the pair acts as a time reference from which the intended recipient can preferentially detect the image carrying photons. These reference photons are themselves made sensitive to the presence of an eavesdropper by traditional polarization-based QKD encoding. Interestingly, the security encoding is performed in the two-dimensional polarization-basis, but the image information is encoded in a much higher-dimensional, hence information-rich, pixel basis. In our example implementation, our images have more than 100 independent pixels. Beyond the secure transmission of images, our approach to the distribution of secure high-dimensional information may create new high-bandwidth approaches to traditional QKD.

DOI
10.1117/12.3000546

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The secure transmission of an image can be accomplished by encoding the image information, securely communicating this information, and subsequently reconstructing the image. As an alternative, here we show how the image itself can be directly transmitted while ensuring that the presence of any eavesdropper is revealed in a way akin to quantum key distribution. We achieve this transmission using a photon-pair source with the deliberate addition of a thermal light source as background noise. One photon of the pair illuminates the object, which is masked from an eavesdropper by adding indistinguishable thermal photons, the other photon of the pair acts as a time reference from which the intended recipient can preferentially detect the image carrying photons. These reference photons are themselves made sensitive to the presence of an eavesdropper by traditional polarization-based QKD encoding. Interestingly, the security encoding is performed in the two-dimensional polarization-basis, but the image information is encoded in a much higher-dimensional, hence information-rich, pixel basis. In our example implementation, our images have more than 100 independent pixels. Beyond the secure transmission of images, our approach to the distribution of secure high-dimensional information may create new high-bandwidth approaches to traditional QKD.
The secure transmission of an image can be accomplished by encoding the image information, securely communicating this information, and subsequently reconstructing the image. Alternatively, here we show how the image itself can be directly transmitted while ensuring that the presence of any eavesdropper is revealed in a way akin to quantum key distribution (QKD). We achieve this transmission using a photon-pair source with the deliberate addition of a thermal light source as background noise. One photon of the pair illuminates the object, which is masked from an eavesdropper by adding indistinguishable thermal photons, the other photon of the pair acts as a time reference with which the intended recipient can preferentially filter the image carrying photons from the background. These reference photons are themselves made sensitive to the presence of an eavesdropper by traditional polarisation-based QKD encoding. Interestingly the security verification is performed in the two-dimensional polarisation-basis, but the image information is encoded in a much higher-dimensional, hence information-rich, pixel basis. In our example implementation, our image comprises of 152 independent pixels. Beyond the secure transmission of images, our approach to the distribution of secure high-dimensional information may offer new high-bandwidth approaches to QKD.
Abstract The secure transmission of an image can be accomplished by encoding the image information, securely communicating this information, and subsequently reconstructing the image. Alternatively, here we show how the image itself can be directly transmitted while ensuring that the presence of any eavesdropper is revealed in a way akin to quantum key distribution (QKD). We achieve this transmission using a photon-pair source with the deliberate addition of a thermal light source as background noise. One photon of the pair illuminates the object, which is masked from an eavesdropper by adding indistinguishable thermal photons, the other photon of the pair acts as a time reference with which the intended recipient can preferentially filter the image carrying photons from the background. These reference photons are themselves made sensitive to the presence of an eavesdropper by traditional polarisation-based QKD encoding. Interestingly the security verification is performed in the two-dimensional polarisation-basis, but the image information is encoded in a much higher-dimensional, hence information-rich, pixel basis. In our example implementation, our image comprises of 152 independent pixels. Beyond the secure transmission of images, our approach to the distribution of secure high-dimensional information may offer new high-bandwidth approaches to QKD.
A limitation of free-space optical communications is the ease with which the information can be intercepted. This limitation can be overcome by hiding the information within background optical noise. We demonstrate the transfer of images over free-space using a photon-pair source emitting two correlated beams. One of these beams contains image information, to which noise is added, and the other correlated beam is used as a heralding trigger so that the intended recipient can differentiate this image signal from the background noise. The system uses spontaneous parametric down-conversion to create photon-pairs with a wide spectral bandwidth and a gated intensified camera to extract the image from the background noise. The high-dimensionality of the image space means that the information content can be many bits per detected photon, whereas the heralding photon can be restricted to a single spatial-mode within a secure fiber which itself could be protected against interception by traditional low-dimensionality quantum key protocols.
Quantum key distribution (QKD) exploits the quantum nature of light to share provably secure keys, allowing secure communication in the presence of an eavesdropper. The first QKD schemes used photons encoded in two states, such as polarization. Recently, much effort has turned to large-alphabet QKD schemes, which encode photons in high-dimensional basis states. Compared to binary-encoded QKD, large-alphabet schemes can encode more secure information per detected photon, boosting secure communication rates, and also provide increased resilience to noise and loss. High-dimensional encoding may also improve the efficiency of other quantum information processing tasks, such as performing Bell tests and implementing quantum gates. Here, we demonstrate a large-alphabet QKD protocol based on high-dimensional temporal encoding. We achieve record secret-key rates and perform the first field demonstration of large-alphabet QKD. This demonstrates a new, practical way to optimize secret-key rates and marks an important step towards transmission of high-dimensional quantum states in deployed networks.
This paper presents a secure image transmission framework for superposition-based quantum communication systems that integrates quantum key distribution (QKD) with one-time-pad encryption. Existing superposition-based image transmission systems achieve reliable image reconstruction over noisy channels but do not provide confidentiality: an eavesdropper intercepting the transmission can recover the image. To address this limitation, we introduce a key-based security layer and analyse its interaction with the quantum modulation and channel coding components. In the proposed approach, a secret key is generated using the BB84 quantum key distribution protocol and then used to encrypt the image data before Hadamard modulation. The system is evaluated both with and without polar channel coding. Simulation results show that encryption does not degrade image quality at the legitimate receiver: its reconstruction performance is indistinguishable from that of the corresponding unsecured baseline under the evaluated conditions. In contrast, the eavesdropper obtains only noise-like plaintext reconstructions, with an empirical PSNR floor of approximately 8.1 dB, even under more favourable channel conditions. Attempts to intercept the BB84 key-generation process remain detectable through the quantum bit error rate. Polar coding provides approximately 8 dB of performance gain for the legitimate receiver; although it can improve ciphertext recovery, it does not improve the eavesdropper’s plaintext reconstruction under the evaluated conditions. These results demonstrate confidentiality without an additional reconstruction-fidelity penalty, while leaving key-rate and protocol costs as separate practical considerations.
Secure communication that allows only the sender and intended recipient of a message to view its content has a long history. Quantum objects, such as single photons are ideal carriers for secure information transmission because, according to the no-cloning theorem [1], it is impossible to create an identical and independent copy of an arbitrary quantum state while its detection leads to the information distortion. BB84 [2,3] is the first quantum cryptography protocol for a quantum key generation and distribution, based on single photon sources. This quantum key is used for coding and decoding of classical information. We propose completely different protocol based on a stochastic decay of an ensemble of radioactive nuclei randomly emitting a stream of gamma-photons. We experimentally demonstrate a method how to transmit classical information containing binary bits (0 or 1) with the help of this stream. Transmission is organized such that eavesdropping is impossible since the presence of information in the stream of randomly emitted gamma-photons can be hidden. Reading of this information needs precise knowledge of the repetition rate of its sending in advance. It is unrealistic for the eavesdropper to disclose this rate, and without knowledge of this parameter it is impossible to make the transmitted information visible.