SQUIDs and flux tunability
Two junctions in a loop create a flux-dependent effective Josephson energy.
Physical intuition
Two junctions in a loop create a flux-dependent effective Josephson energy. This is the starting point for understanding how superconducting circuit parameters determine quantum energy levels and dynamics.
Deep dive: how the mechanism works
Interference between the junction tunneling amplitudes makes the effective nonlinearity sensitive to applied flux.
How the quantum phenomenon appears
Flux-tunable transmons use a SQUID in place of one junction. To establish the predicted quantum behavior, connect the circuit Hamiltonian to a measured transition, coherence experiment, gate benchmark or calibrated readout signal.
Assumptions and limitations
Research and simulation exercise
Identify the tunable parameters, predict the observable from the stated model, and sweep one parameter while holding the others fixed. Compare against a simpler reference model, quantify loss and uncertainty, and state which observations would falsify the hypothesis.
Connect the ideas
See the chapter guide and further reading.