Abstract
In quantum communication networks, wires represent well-defined trajectories along which quantum systems are transmitted. In spite of this, trajectories can be used as a quantum control to govern the order of different noisy communication channels, and such a control has been shown to enable the transmission of information even when quantum communication protocols through well-defined trajectories fail. This result has motivated further investigations on the role of the superposition of trajectories in enhancing communication, which revealed that the use of quantum control of parallel communication channels, or of channels in series with quantum-controlled operations, can also lead to communication advantages. Building upon these findings, here we experimentally and numerically compare different ways in which two trajectories through a pair of noisy channels can be superposed. We observe that, within the framework of quantum interferometry, the use of channels in series with quantum-controlled operations generally yields the largest advantages. Our results contribute to clarify the nature of these advantages in experimental quantum-optical scenarios, and showcase the benefit of an extension of the quantum communication paradigm in which both the information exchanged and the trajectory of the information carriers are quantum.
Highlights
The ability to establish secure communication linkages is of paramount importance in any information technology
We focus on the following four points: (i) we illustrate that all three schemes use the same resource when considering experimental quantum interferometry; (ii) we show that this resource is the coupling of the degree of freedom carrying the information to the trajectory degree of freedom; (iii) we experimentally prove that, for the set of tested noisy channels, the superposition of channels in series with quantum-controlled operations features the highest performance; and (iv) we numerically show that, in the vast majority of cases, this holds for generic randomly generated channels
We present our results for the three combinations of the noisy channels described in Eqs. (8)–(10)
Summary
The ability to establish secure communication linkages is of paramount importance in any information technology. Quantum cryptography protocols [1,2] achieve this in a stunning way, enabling a sender and receiver to communicate securely even in the presence of an eavesdropper with unlimited computational power. The crucial ingredient for this feat is the availability of reliable transmission lines for quantum. In this framework, any noisy process affecting the transmission is attributed to the presence of an eavesdropper, and when the noise exceeds a given threshold, the security of the communication is considered compromised. Any noisy process affecting the transmission is attributed to the presence of an eavesdropper, and when the noise exceeds a given threshold, the security of the communication is considered compromised For this reason, the mitigation of any noise arising from faulty transmission lines is an integral part of the efforts to enable secure communication
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