Cross-resonance gates
Driving one coupled qubit near another qubit frequency produces an effective conditional rotation.
Physical intuition
Driving one coupled qubit near another qubit frequency produces an effective conditional rotation. This is the starting point for understanding how superconducting circuit parameters determine quantum energy levels and dynamics.
Deep dive: how the mechanism works
Microwave driving combined with fixed coupling generates a ZX interaction that can be echoed and calibrated.
How the quantum phenomenon appears
Fixed-frequency transmon architectures implement entangling gates with cross resonance. 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.