Figure 1. Two arrays of superconducting qubits.

(a) Charge-qubit array: Nearest-neighbor charge qubits Q_n and Q_n+1 are coupled by a large Josephson junction with coupling energy E_Jc (shown as a crossed rectangle). (b) Flux-qubit array: Nearest-neighbor flux qubits are coupled by a coupler consisting of a flux-biased loop that is interrupted by two large Josephson junctions (each with coupling energy E_Jc) and a small Josephson junction with coupling energy βE_Jc, where . In (a) and (b), Φ_q is the flux applied to each qubit loop. (c) Main components of a charge qubit, where a superconducting island (denoted as a solid circle) is connected to two Josephson junctions (each with coupling energy and capacitance C_J) and biased by a voltage V_g through a gate capacitance . (d) Main components of a flux qubit, where two Josephson junctions, each with coupling energy , connects a symmetric dc SQUID biased by a flux Φ_s.