Josephson junctions · Circuit QED · Quantum processors
Quantum circuits.
Engineered atoms.
How do superconducting condensates, Josephson junctions and microwave circuits become coherent qubits, entangling gates and quantum processors?
$$H/\hbar=\omega_c a^\dagger a+\frac{\omega_e}{2}\sigma_z+g(a^\dagger\sigma_-+a\sigma_+)$$
Superconductivity alone does not make a useful qubit.
Superconducting quantum circuits combine macroscopic phase coherence, Josephson tunneling and microwave electromagnetic modes to create controllable quantum degrees of freedom. Circuit quantization, anharmonicity, measurement and decoherence determine what is observable and useful.
Ordinary superconducting wiring and resonators can behave approximately classically. A usable qubit requires quantized energy levels, sufficient anharmonicity, coherent control and high-fidelity measurement. This library distinguishes physical mechanisms from engineering assumptions.
Enter the subject.
Chapter 01 · 8 conceptsSuperconductivity and Josephson PhysicsBCS pairing, flux quantization and Josephson nonlinearities.Chapter 02 · 10 conceptsCircuit Quantization and Qubit ModalitiesHamiltonians, zero-point fluctuations, transmon, flux qubit and fluxonium.Chapter 03 · 8 conceptsCircuit QED and DecoherenceMicrowave cavities, dispersive coupling, noise and coherence.Chapter 04 · 5 conceptsControl and Entangling GatesPulse design, CZ, cross resonance and parametric interactions.Chapter 05 · 6 conceptsQuantum Measurement and Parametric DevicesReadout, Josephson amplification, squeezing and open-system dynamics.Chapter 06 · 5 conceptsError Correction and EngineeringStabilizers, simulation, noise spectroscopy and scaling.
Follow the physical chain.
01 / ElectromagnetismDesign the circuitCapacitance, inductance, junctions and microwave modes.
02 / Quantum opticsControl and entangleQubit Hamiltonians, pulses, couplers and decoherence.
03 / ExperimentMeasure and correctDispersive readout, noise, stabilizers and benchmarks.