Entanglement and Bell States in Superconducting Flux Qubits

TL;DR

This paper explores how superconducting flux qubits can be entangled into Bell states through strong Josephson junction coupling, highlighting the conditions for maximal entanglement in such macroscopic quantum systems.

Contribution

It demonstrates the possibility of achieving Bell states in coupled flux qubits by tuning Josephson coupling and magnetic flux, emphasizing the role of two-qubit tunneling processes.

Findings

Strong Josephson coupling enables Bell states in flux qubits.

Two-qubit tunneling dominates over single-qubit tunneling in certain regimes.

Bell states are achievable with specific magnetic flux and Josephson energies.

Abstract

We theoretically study macroscopic quantum entanglement in two superconducting flux qubits. To manipulate the state of two flux qubits, a Josephson junction is introduced in the connecting loop coupling the qubits. Increasing the coupling energy of the Josephson junction makes it possible to achieve relatively strong coupling between the qubits, causing two-qubit tunneling processes even dominant over the single-qubit tunneling process in the states of two qubits. It is shown that due to the two-qubit tunneling processes both the ground state and excited state of the coupled flux qubits can be a Bell type state, maximally entangled. The parameter regimes for the Bell states are discussed in terms of magnetic flux and Josephson coupling energies.