Superconducting qubits are artificial atoms made from electrical circuits cooled to millikelvin temperatures. Their quantum states come from collective circuit modes rather than individual microscopic particles.
The central trick is to combine superconductors with a nonlinear element, usually a Josephson junction, so the circuit has discrete energy levels that can act as a qubit.
Why They Are Useful
- They are fabricated with lithographic techniques related to conventional microelectronics.
- They can be controlled quickly with microwave pulses.
- They couple naturally to resonators, which enables circuit QED readout.
- Their parameters can be engineered by changing circuit geometry, capacitance, inductance, and junction energy.
Main Challenge
The same electromagnetic coupling that makes these qubits controllable also makes them sensitive to noise. Useful devices require careful design around coherence, filtering, shielding, materials, and calibration.
Common Families
- Transmon qubits
- Flux qubits
- Fluxonium qubits
- Tunable coupler circuits