Observing interferences between past and future quantum states in resonance fluorescence

Area of Science:

• Quantum Computing
• Quantum Information Science
• Solid-State Physics

Background:

• Superconducting qubits are fundamental building blocks for quantum computers.
• Understanding qubit dynamics, especially relaxation, is crucial for quantum computation.
• Weak measurement offers a non-demolition probe of quantum systems.

Purpose of the Study:

• To measure the fluorescence of a resonantly driven superconducting qubit in the time domain.
• To use prior preparation and single-shot measurements for conditional averaging of fluorescence records.
• To reveal quantum features and probe relaxation dynamics using weak values.

Main Methods:

• Time-domain fluorescence measurements of a superconducting qubit.
• Conditional averaging of measurement results based on past and future qubit states.
• Application of weak measurement principles to probe quantum dynamics.

Main Results:

• Observed interference patterns characteristic of quantum weak values.
• Demonstrated conditional averages exceeding classical bounds.
• Direct probing of the jump operator associated with qubit relaxation.

Conclusions:

• The experimental results validate a generalized quantum mechanics theory for open systems with known past and future.
• Conditional averaging of weak measurements provides a powerful tool for studying quantum dynamics.
• This work offers new insights into the fundamental behavior of superconducting qubits.