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Register a new userSelf-healing high-dimensional quantum key distribution using hybrid spin-orbit Bessel states
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Using spatial modes for quantum key distribution (QKD) has become highly topical due to their infinite dimensionality, promising high information capacity per photon. However, spatial distortions reduce the feasible secret key rates and compromise the security of a quantum channel. In an extreme form such a distortion might be a physical obstacle, impeding line-of-sight for free-space channels. Here, by controlling the radial degree of freedom of a photons spatial mode, we are able to demonstrate hybrid high-dimensional QKD through obstacles with self-reconstructing single photons. We construct high-dimensional mutually unbiased bases using spin-orbit hybrid states that are radially modulated with a non-diffracting Bessel-Gaussian (BG) profile, and show secure transmission through partially obstructed quantum links. Using a prepare-measure protocol we report higher quantum state self-reconstruction and information retention for the non-diffracting BG modes as compared to Laguerre-Gaussian modes, obtaining a quantum bit error rate (QBER) that is up to 3 times lower. This work highlights the importance of controlling the radial mode of single photons in quantum information processing and communication as well as the advantages of QKD with hybrid states.
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We propose a schematic setup of quantum key distribution (QKD) with an improved secret key rate based on high-dimensional quantum states. Two degrees-of-freedom of a single photon, orbital angular momentum modes, and multi-path modes, are used to encode secret key information. Its practical implementation consists of optical elements that are within the reach of current technologies such as a multiport interferometer. We show that the proposed feasible protocol has improved the secret key rate with much sophistication compared to the previous 2-dimensional protocol known as the detector-device-independent QKD.
It is known that measurement-device-independent quantum key distribution (MDI-QKD) provides ultimate security from all types of side-channel attack against detectors at the expense of low key generation rate. Here, we propose MDI-QKD using 3-dimensional quantum states and show that the protocol improves the secret key rate under the analysis of mismatched-basis statistics. Specifically, we analyze security of the 3d-MDI-QKD protocol with uncharacterized sources, meaning that the original sources contain unwanted states instead of expected one. We simulate secret key rate of the protocol and identify the regime where the key rate is higher than the protocol with the qubit MDI-QKD.
Reference-frame-independent quantum key distribution (RFI QKD) protocol can reduce the requirement on the alignment of reference frames in practical systems. However, comparing with the Bennett-Brassard (BB84) QKD protocol, the main drawback of RFI QKD is that Alice needs to prepare six encoding states in the three mutually unbiased bases (X, Y, and Z), and Bob also needs to measures the quantum state with such three bases. Here, we show that the RFI QKD protocol can be secured in the case where Alice sends fewer states. In particular, we find that transmitting three states (two eigenstates of the Z basis and one of the eigenstates in the X basis) is sufficient to obtain the comparable secret key rates and the covered distances, even when the security against coherent attacks with statistical fluctuations of finite-key size is considered. Finally, a proof-of-principle experiment based on time-bin encoding is demonstrated to show the feasibility of our scheme, and its merit to simplify the experimental setup.
Quantum Key Distribution (QKD) provides an efficient means to exchange information in an unconditionally secure way. Historically, QKD protocols have been based on binary signal formats, such as two polarisation states, and the transmitted information efficiency of the quantum key is intrinsically limited to 1 bit/photon. Here we propose and experimentally demonstrate, for the first time, a high-dimensional QKD protocol based on space division multiplexing in multicore fiber using silicon photonic integrated lightwave circuits. We successfully realized three mutually unbiased bases in a four-dimensional Hilbert space, and achieved low and stable quantum bit error rate well below both coherent attack and individual attack limits. Compared to previous demonstrations, the use of a multicore fiber in our protocol provides a much more efficient way to create high-dimensional quantum states, and enables breaking the information efficiency limit of traditional QKD protocols. In addition, the silicon photonic circuits used in our work integrate variable optical attenuators, highly efficient multicore fiber couplers, and Mach-Zehnder interferometers, enabling manipulating high-dimensional quantum states in a compact and stable means. Our demonstration pave the way to utilize state-of-the-art multicore fibers for long distance high-dimensional QKD, and boost silicon photonics for high information efficiency quantum communications.
High-dimensional quantum key distribution (QKD) provides ultimate secure communication with secure key rates that cannot be obtained by QKD protocols with binary encoding. However, so far the proposed protocols required additional experimental resources, thus raising the cost of practical high-dimensional systems and limiting their use. Here, we analyze and demonstrate a novel scheme for fiber-based arbitrary-dimensional QKD, based on the most popular commercial hardware for binary time bins encoding. Quantum state transmission is tested over 40 km channel length of standard single-mode fiber, exhibiting a two-fold enhancement of the secret key rate in comparison to the binary Coherent One Way (COW) protocol, without introducing any hardware modifications. This work holds a great potential to enhance the performance of already installed QKD systems by software update alone.
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