Macroscopic Einstein-Podolsky-Rosen pairs in superconducting circuits

We propose an efficient approach to prepare Einstein-Podolsky-Rosen (EPR) pairs in currently existing Josephson nanocircuits with capacitive couplings. In these fixed coupling circuits, two-qubit logic gates could be easily implemented while, strictly speaking, single-qubit gates cannot be easily realized. For a known two-qubit state, conditional single-qubit operation could still be designed to evolve only the selected qubit and keep the other qubit unchanged; the rotation of the selected qubit depends on the state of the other one. These conditional single-qubit operations allow us to deterministically generate the well-known Einstein-Podolsky-Rosen pairs, represented by EPR-Bell (or Bell) states. Quantum-state tomography is further proposed to experimentally confirm the generation of these states. The decays of the prepared EPR pairs are analyzed using numerical simulations. Possible application of the generated EPR pairs to test Bell's Inequality is also discussed.