Light-matter decoupling and $A^2$ term detection in superconducting   circuits
  We study the spontaneous emission of a qubit interacting with a one-dimensional waveguide through a realistic minimal-coupling interaction. We show that the diamagnetic term $A^2$ leads to an effective decoupling of a single qubit from the electromagnetic field. This effects is observable at any range of qubit-photon couplings. For this we study a setup consisting of a transmon that is suspended over a transmission line. We prove that the relative strength of the $A^2$ term is controlled with the qubit-line separation and show that, as a consequence, the spontaneous emission rate of the suspended transmon onto the line can increase with such separation, instead of decreasing. 
Juan Jos\'e Garc\'ia-Ripoll, Borja Peropadre, Simone De Liberato
quant-ph cond-mat.mes-hall cond-mat.supr-con