Generation and Control of Greenberger-Horne-Zeilinger Entanglement in Superconducting Circuits

Going beyond the entanglement of microscopic objects (such as photons, spins, and ions), here we propose an efficient approach to produce and control the quantum entanglement of three macroscopic coupled superconducting qubits. By conditionally rotating, one by one, selected Josephson-charge qubits, we show that their Greenberger-Horne-Zeilinger (GHZ) entangled states can be deterministically generated. The existence of GHZ correlations between these qubits could be experimentally demonstrated by effective single-qubit operations followed by high-fidelity single-shot readouts. The possibility of using the prepared GHZ correlations to test the macroscopic conflict between the noncommutativity of quantum mechanics and the commutativity of classical physics is also discussed.

Figure 1

Three capacitively coupled SQUID-based charge qubits. The quantum states of three Cooper-pair boxes (i.e., qubits) are manipulated by controlling the applied gate voltages $V_j(j=1,2,3)$, and external magnetic fluxes ${\Phi }_j$ (penetrating the SQUID loops). The circuit can be generalized to include more qubits.