Abstract
Quantum networks are the ultimate target in quantum communication, where many connected users can share information carried by quantum systems. The keystones of such structures are the reliable generation, transmission and manipulation of quantum states. Two-dimensional quantum states, qubits, are steadily adopted as information units. However, high-dimensional quantum states, qudits, constitute a richer resource for future quantum networks, exceeding the limitations imposed by the ubiquitous qubits. The generation and manipulation of such $D$-level systems have been improved over the last ten years, but their reliable transmission between remote locations remains the main challenge. Here, we show how a recent air-core fiber supporting orbital angular momentum (OAM) modes can be exploited to faithfully transmit $D$-dimensional states. Four OAM quantum states and their superpositions are created, propagated in a 1.2 km long fiber and detected with high fidelities. In addition, three quantum key distribution (QKD) protocols are implemented as concrete applications to assert the practicality of our results. This experiment enhances the distribution of high-dimensional quantum states, attesting the orbital angular momentum as vessel for the future quantum network.
Highlights
Quantum communication, i.e., the faithful transmission of quantum states between separated users, has established itself in the last decade due to its inherently and fascinating connection to quantum nonlocality and ultimate communication security [1]
We prove the first transmission of highdimensional quantum states, encoded using their orbital angular momentum, by exploiting a recently developed air-core fiber [44], which transcend the constraints of previous approaches
Photons carrying orbital angular momentum are characterized by a helical phase factor ei θ, where θ is the azimuthal coordinate and is an unbounded integer value representing the quanta of OAM that each photon possesses [45]
Summary
I.e., the faithful transmission of quantum states between separated users, has established itself in the last decade due to its inherently and fascinating connection to quantum nonlocality and ultimate communication security [1]. High-dimensional quantum states have been implemented by exploiting position-momentum [25,26,27] and orbital-angular-momentum (OAM) [28,29,30] degrees of freedom, spatial modes in multicore fibres [31,32,33], and time-energy and time-bin encoding [34,35,36]. We prove the first transmission of highdimensional quantum states, encoded using their orbital angular momentum, by exploiting a recently developed air-core fiber [44], which transcend the constraints of previous approaches. It presents an enhanced preservation of mode orthogonality, which results in a negligible mode mixing between the OAM modes simultaneously propagated. Our results settle the orbital angular momentum as one of the most promising degrees of freedom to distribute high-dimensional quantum states in a future quantum network
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