Quantum walk inspired algorithm for directly measuring two-qubit entanglement

Abstract Direct measurement of entanglement is an efficient method for obtaining the degree of entanglement without full reconstruction of the quantum state. But most of the current entanglement direct measurement schemes are designed for the states in specific physical systems, and are not universal for different physical systems. So, in this paper, we want to design a universal direct measurement algorithm for the entanglement of two-qubit states, where universal means that the algorithm does not depend on specific physical systems. Although the conventional quantum walk (QW) model does not have this universal property, we find that by introducing auxiliary qubits and CNOT gates in quantum circuits, a generalized QW model can be realized in any qubit system, i.e. it is universal for different physical systems. Inspired by the universal property of this generalized QW model, a universal quantum algorithm is designed for directly measuring the entanglement degree of two-qubit states, which we call the QW inspired algorithm. To demonstrate the feasibility of the algorithm, analytical calculations and numerical simulations for three representative quantum states are studied. The results show that the algorithm can be used to directly measure two-qubit entanglement, and the universality of the algorithm guarantees that it works not only in optical systems but also in any other physical system. Furthermore, this algorithm may find more applications in other quantum information tasks necessitating qubit–qubit coupling.