Tunneling out of metastable vacuum in a system consisting of two   capacitively coupled phase qubits
  Using a powerful combination of Coleman's instanton technique and the method of Banks and Bender, the exponential factor for the zero temperature rate of tunneling out of metastable vacuum in a system of two identical capacitively coupled phase qubits is calculated in closed form to second order in asymmetry parameter for a special case of intermediate coupling C=C_J/2. 
Andrei Galiautdinov