Superconducting circuits

Thanks. *BIG* chuckle if a lawyer sez "IANAL"...

In sci.electronics.design Guy Macon wrote: : going around each loop is independent in the upper circuit. : Why would an electron coming out of L1 prefer the path through : the zero ohm center leg rather than the zero ohm L2 leg?

If you can tolerate cheating that the current is granular (in reality it is smooth): when the electron tries to choose the L2 leg, it constitutes a pulse whose duration-times-amperage product equals the electron charge. Such a pulse generates an opposing voltage L2*dI/dt, which makes the electron to choose the easier zero-inductance path through the center leg.

You can probably extend the argument into the smooth-current case by taking the relevant limits appropriately.

Regards, Mikko

In sci.electronics.design John Larkin wrote: : The middle leg could certainly be constructed so that there is zero : (or even negative, if that turns you on) mutual inductance between the : two loops.

True, and I can't constrain myself from suggesting an easy-to visualize zero-mutual case:

Shrink the middle leg into a point, and rotate the L1 loop 90 degrees so that the loop will come out of the paper (computer screen) plane. Then the L1 creates B_y field and the L2 creates B_z field which won't couple to each other. Here x-axis is assumed to extend towards the right side of the paper, y-axis toward the top side, and z-axis comes out of the sheet.

If one wants a planar circuit, the L1 can be made a gradiometric loop pair generating dB_z/dx and L2 made an orthogonal loop pair generating dB_z/dy.

Regards, Mikko