Concept 20 of 42 · Circuit QED and Decoherence

Circuit quantum electrodynamics

Artificial atoms interact with quantized microwave cavity fields.

01 / Mathematical framework

$$H/\hbar=\omega_ra^\dagger a+\frac{\omega_q}{2}\sigma_z+g(a^\dagger\sigma_-+a\sigma_+)$$

Physical intuition

Artificial atoms interact with quantized microwave cavity fields. This is the starting point for understanding how superconducting circuit parameters determine quantum energy levels and dynamics.

Deep dive: how the mechanism works

Capacitive or inductive coupling exchanges excitations between a resonator and a superconducting qubit.

How the quantum phenomenon appears

Vacuum Rabi splitting probes coherent coupling. 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

The Jaynes-Cummings approximation neglects higher qubit levels and counter-rotating terms.

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

Microwave resonators Dispersive regime

See the chapter guide and further reading.

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ΦCircuit quantum electrodynamics