Longitudinal and Nonlinear Coupling for High-Fidelity Readout of a Superconducting Qubit

Area of Science:

• Quantum Computing
• Superconducting Circuits
• Quantum Measurement

Background:

• Quantum state measurement in superconducting quantum computation is slower and less accurate than gate operations.
• Current measurement techniques risk qubit state transitions due to strong coupling and readout signals.

Purpose of the Study:

• To design a novel architecture for improved superconducting qubit measurement.
• To implement a longitudinal interaction scheme with enhanced qubit-resonator coupling.
• To minimize errors during quantum state readout.

Main Methods:

• Developed a novel architecture enabling genuine longitudinal qubit-resonator interaction.
• Eliminated residual transversal couplings in the qubit-resonator system.
• Introduced resonator nonlinearity to reduce decay and measurement-induced errors.
• Employed a multilevel readout protocol for enhanced measurement fidelity.

Main Results:

• Achieved a high quantum state measurement fidelity of 99.8%.
• Reached this fidelity within a rapid 202 nanosecond timeframe.
• Demonstrated successful measurement without the need for first-stage amplification.

Conclusions:

• The novel architecture offers a significant advancement in superconducting qubit measurement speed and fidelity.
• This approach effectively mitigates common error sources in quantum state readout.
• The architecture shows great promise for future superconducting quantum processors.