Parallel multi-two-qubit SWAP gate via quantum nondemolition interaction of orbital-angular-momentum light and an atomic ensemble

Nowadays, the quantum SWAP gate has become an integral part of quantum computing, so the investigation of methods for its realization seems to be an important practical problem for various quantum-optical and information applications. In the present paper, we propose a scheme for performing a SWAP logic operation in discrete variables in the framework of quantum nondemolition interaction between an atomic ensemble and a multimode light with orbital angular momentum. We discuss in detail the procedure for revealing two-qubit closed subsystems on a set of atomic and field states for different values of the driving field orbital momentum. We also demonstrate the possibility of implementing a parallel multi-two-qubit quantum SWAP gate.