The escape physics of single shot measurement of flux qubit with dcSQUID

Abstract

In most experiments on flux qubits,the "measurement" is performed by coupling the system to a dc SQUID and recording the distribution of switching currents for the latter;this measurement protocol is very far from the classic von Neumann ("projective") scheme,in that very little information is obtained from a single run,rather one has to repeat the experiment tens of thosands of times to extract anything useful.Here, concentrating on the equlibrium behavior of the flux qubit,we carry out an analytic calculation of the dc-SQUID switching current distribution as a function of external bias flux on the qubit,and compare our predictions with the data from experiments conducted at Delft and NTT.