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Register a new userCoherent one-way quantum conference key agreement based on twin field
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Quantum conference key agreement (CKA) enables key sharing among multiple trusted users with information-theoretic security. Currently, the key rates of most quantum CKA protocols suffer from the limit of the total efficiency among quantum channels. Inspired by the coherent one-way and twin-field quantum key distribution (QKD) protocols, we propose a quantum CKA protocol of three users. Exploiting coherent states with intensity 0 and $mu$ to encode logic bits, our protocol can break the limit. Additionally, the requirements of phase randomization and multiple intensity modulation are removed in our protocol, making its experimental demonstration simple.
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Quantum networks will provide multi-node entanglement over long distances to enable secure communication on a global scale. Traditional quantum communication protocols consume pair-wise entanglement, which is sub-optimal for distributed tasks involving more than two users. Here we demonstrate quantum conference key agreement, a quantum communication protocol that exploits multi-partite entanglement to efficiently create identical keys between N users with up to N-1 rate advantage in constrained networks. We distribute four-photon Greenberger-Horne-Zeilinger (GHZ) states generated by high-brightness, telecom photon-pair sources across up to 50 km of fibre, implementing multi-user error correction and privacy amplification on resulting raw keys. Under finite-key analysis, we establish $1.15times10^6$ bits of secure key, which are used to encrypt and securely share an image between the four users in a conference transmission. We have demonstrated a new protocol tailored for multi-node networks leveraging low-noise, long-distance transmission of GHZ states that will pave the way forward for future multiparty quantum information processing applications.
Conference key agreement (CKA), or multipartite key distribution, is a cryptographic task where more than two parties wish to establish a common secret key. A composition of bipartite quantum key distribution protocols can accomplish this task. However, the existence of multipartite quantum correlations allows for new and potentially more efficient protocols, to be applied in future quantum networks. Here, we review the existing quantum CKA protocols based on multipartite entanglement, both in the device-dependent and the device-independent scenario.
The intense research activity on Twin-Field (TF) quantum key distribution (QKD) is motivated by the fact that two users can establish a secret key by relying on single-photon interference in an untrusted node. Thanks to this feature, variants of the protocol have been proven to beat the point-to-point private capacity of a lossy quantum channel. Here we generalize the main idea of the TF-QKD protocol introduced by Curty et al. to the multipartite scenario, by devising a conference key agreement (CKA) where the users simultaneously distill a secret conference key through single-photon interference. The new CKA is better suited to high-loss scenarios than previous multipartite QKD schemes and it employs for the first time a W-class state as its entanglement resource. We prove the protocols security in the finite-key regime and under general attacks. We also compare its performance with the iterative use of bipartite QKD protocols and show that our truly multipartite scheme can be advantageous, depending on the loss and on the state preparation.
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.
Coherent-one-way quantum key distribution (COW-QKD), possessing the simple experimental setup and the ability against the photon-number-splitting attack, has been implemented in various experiments and commercial applications. However, recent works have proved that current COW-QKD with key rate scaling linearly with transmittance is totally insecure under the zero-error attack. This conclusion leads to a crucial consequence that all the current attempts for practicalization are in vain. To solve this pending issue, here we conduct a minor revision on original COW-QKD while maintaining the original experimental setup as well as the simplicity of implementation. By more precisely estimating the amount of leaked information, we provide an explicit unconditional secure key rate which scales with $0.7%$ of the bound that quadratically scales with transmittance. Our work provides a revised COW-QKD which guarantees the availability of the current implementations of COW-QKD within 100 km and establishes the theoretical foundations for further application.
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