Abstract
High-dimensional quantum key distribution (QKD) allows achievement of information-theoretic secure communications, providing high key-generation rates, which cannot, in principle, be obtained by QKD protocols with binary encoding. Nonetheless, the amount of experimental resources needed increases as the quantum states to be detected belong to a larger Hilbert space, thus raising the costs of practical high-dimensional systems. Here, we present an alternative scheme for fiber-based four-dimensional QKD, with time and phase encoding and one-decoy state technique. Quantum state transmission is tested over different channel lengths up to 145 km of standard single-mode fiber, evaluating the enhancement of the secret key rate in comparison to the three-state two-dimensional BB84 protocol, which is tested with the same experimental setup. Our scheme allows measurement of the four-dimensional states with a simplified and compact receiver, where only two single-photon detectors are necessary, thus making it a cost-effective solution for practical and fiber-based QKD.
Highlights
As the constant advancement in quantum computing is threatening the security of current cryptographic systems, our society needs an alternative technology to safely transmit sensitive data and confidential information [1]
In well-established quantum key distribution (QKD) protocols such as the BB84 [2], each bit of the key is carried by a single photon, which is prepared in order to span a set of different quantum states belonging to a two-dimensional Hilbert space, i.e., qubits
The result is an increase in the secret key rate achievable by high-dimensional QKD, as compared with standard QKD protocols with binary encoding (d = 2), at least until the overall losses are low enough to keep negligible the random dark counts at the receiver [8,9,10]
Summary
As the constant advancement in quantum computing is threatening the security of current cryptographic systems, our society needs an alternative technology to safely transmit sensitive data and confidential information [1]. In well-established QKD protocols such as the BB84 [2], each bit of the key is carried by a single photon, which is prepared in order to span a set of different quantum states belonging to a two-dimensional Hilbert space, i.e., qubits. Using high-dimensional states improves the robustness to the noise affecting the communication, allowing for a higher threshold value of the quantum bit error rate (QBER).
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