Adithi Ajith | Searcharxiv

arXiv2023

Quantum walk-based protocol for secure communication between any two directly connected nodes on a network

The utilization of quantum entanglement as a cryptographic resource has superseded conventional approaches to secure communication. Security and fidelity of intranetwork communication between quantum devices is the backbone of a quantum network. This work presents an algorithm that generates entanglement between any two directly connected nodes of a quantum network to be used as a resource to enable quantum communication across that pair in the network. The algorithm is based on a directed discrete-time quantum walk and paves the way for private inter-node quantum communication channels in the network. We also present the simulation results of this algorithm on random networks generated from various models. We show that after implementation, the probability of the walker being at all nodes other than the source and target is negligible, and this holds independent of the random graph generation model. This constitutes a viable method for the practical realisation of secure communication over any random network topology.

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arXiv2022

To share and not share a singlet: control qubit and nonclassicality in teleportation

The superposition principle provides us the opportunity to unfold many surprising facts. One such fact leads to the generation of entanglement which may allow one to teleport an unknown quantum state from one location to another. We try to understand the role of superposition in the process of quantum teleportation. We consider, within the scenario of quantum teleportation, a set-up where the sender and the receiver are in a superposed situation of using a maximally entangled state and not using any entangled state in the teleportation protocol, controlled by a qubit. We address two distinct protocols: in the first case, the sender and the receiver do nothing when they do not have the authority to use entanglement, while in the second case, they still use classical communication even if they do not use entanglement. After accomplishing the protocols, we operate a Hadamard gate on the control qubit, measure the control qubit's state, and consider the outcome corresponding to a particular state of the control. We compare the protocol's fidelity with the maximum fidelity achievable through classical resources only. In particular, we provide conditions to achieve nonclassical fidelity in teleportation, in the presence of the control qubit. To explore if there is any quantum advantage (advantage of superposition present in the control qubit), we compare the fidelities of the control qubit-based protocols with the fidelity achieved in a situation where the two parties are in a classical mixture of using and not using the maximally entangled state. We observe that there exists a wide range of parameters defining the initial state of the control qubit for which our protocols provide quantum advantage. To analyse the role of superposition quantitatively, we discuss whether the amount of quantum advantage can be expressed in terms of quantum coherence present in the state of the control qubit.

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