Quantum State Transfer and Network Engineering

Man‐Hong Yung

Quantum state transfer is an important task in quantum information processing. It is known that one can engineer the couplings of a one-dimensional spin chain to achieve the goal of perfect state transfer. To leverage the value of these spin chains, a spin star is potentially useful for connecting different parts of a quantum network. In this work, we extend the spin-chain engineering problem to the problems with a topology of a star network. We show that a permanently coupled spin star can function as a network switch for transferring quantum states selectively from one node to another by varying the local potentials only. Together with one-dimensional chains, this result allows applications of quantum state transfer to be applied to more general quantum networks.

Andrea Conti, Andrea Giani, Moe Z. Win

M. Bertolotti, Fabio Antonio Bovino, Concita Sibilia

Markku Hahto, Jyrki Piilo, Johannes Nokkala

Abstract Quantum state transfer is the act of transferring quantum information from one system in a quantum network to another without physically transporting carriers of quantum information, but instead engineering a Hamiltonian such that the state of the sender is transferred to the receiver through the dynamics of the whole network. A generalization of quantum state transfer called quantum routing concerns simultaneous transfers between multiple pairs in a quantum network, imposing limitations on its structure. This study considers transfer of Gaussian states over noisy quantum networks with modular structure, which have been identified as a suitable platform for quantum routing. Two noise models are compared, affecting either the network topology or the network constituents, studying their effects on both the transfer fidelities and the network properties. The two models are found to affect different features of the network allowing for the identification and quantification of the noise. These features are then used as a guide toward different strategies for the compensation of the noise, and to examine how the compensation strategies perform. The results show that in general, modular networks are more robust to noise than monolithic ones.

Günter Mahler A, Volker A. Weberruß

Man‐Hong Yung, Sougato Bose

We show how to achieve perfect quantum state transfer and construct effective two-qubit gates between distant sites in engineered bosonic and fermionic networks. The Hamiltonian for the system can be determined by choosing an eigenvalue spectrum satisfying a certain condition, which is shown to be both sufficient and necessary in mirror-symmetrical networks. The natures of the effective two-qubit gates depend on the exchange symmetry for fermions and bosons. For fermionic networks, the gates are entangling (and thus universal for quantum computation). For bosonic networks, though the gates are not entangling, they allow two-way simultaneous communications. Protocols of entanglement generation in both bosonic and fermionic engineered networks are discussed.