Korsbakken et al.
[1] J.Korsbakken,F.K.Wilhelm"]and K.B.Whaley,Physics Scripta T137,014022 (2009)
A strict experimental test of macroscopic realism in a superconducting flux qubit
Macroscopic realism is the name for a class of modifications to quantum theory that allow macroscopic objects to be described in a measurement-independent fashion, while largely preserving
a fully quantum mechanical description of the microscopic world. Objective collapse theories are examples which attempt to provide a physical mechanism for wavefunction collapse, and thereby aim to solve the quantum measurement problem. Here we describe and implement an experimental protocol capable of constraining theories of this class, and show how it is related to the original Leggett-Garg test, yet more noise tolerant and conceptually transparent. By conducting a set of simple ‚prepare, shuffle, measure‘ tests in a superconducting flux qubit, we rule out (by over 77 standard deviations) those theories which would deny coherent superpositions of 170 nA currents over a 9 ns timescale. Further, we address the ‚clumsiness loophole‘ by determining classical disturbance in a set of control experiments.
The escape physics of single shot measurement of flux qubit with dcSQUID
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.