Quantum oscillations in two coupled charge qubits
  Despite an apparent progress in implementing individual solid-state qubits, there have been no experimental reports so far on multi-bit gates required for building a real quantum computer. Here we report a new circuit comprising two coupled charge qubits. Using a pulse technique, we coherently mix quantum states and observe quantum oscillations whose spectrum reflects interaction between the qubits. Our results demonstrate the feasibility of coupling of multiple solid-state qubits and indicate the existence of entangled two-qubit states. 
Yu. A. Pashkin, T. Yamamoto, O. Astafiev, Y. Nakamura, D. V. Averin,   J. S. Tsai