Microwave fidelity studies by varying antenna coupling.

Area of Science:

• Quantum chaos and quantum information science.
• Experimental condensed matter physics.

Background:

• Fidelity decay quantifies the loss of quantum information in a system.
• Microwave billiards serve as a controllable experimental platform for studying quantum chaotic phenomena.

Purpose of the Study:

• To experimentally investigate the decay of fidelity in a microwave billiard.
• To analyze the effect of varying antenna coupling on fidelity decay.
• To compare experimental results with theoretical predictions from a modified Van Vleck-Wigner-Ziman (VWZ) approach.

Main Methods:

• Experimental setup involving a microwave billiard with a variable coupling antenna.
• Three distinct antenna terminators were used: hard-wall reflection, open-wall reflection, and a 50 Ω load (representing a fully open channel).
• Measurement of coupling fidelity as a function of antenna coupling strength.

Main Results:

• The coupling fidelity was experimentally measured for the three different antenna termination conditions.
• A model describing fidelity decay using an effective Hamiltonian with a complex coupling constant was developed.
• Quantitative agreement was achieved between the experimental data and the theoretical predictions from the modified VWZ approach.

Conclusions:

• The study successfully characterized fidelity decay in a microwave billiard system.
• The experimental findings support the validity of the theoretical model incorporating a complex coupling constant.
• This work provides a quantitative link between experimental measurements and theoretical frameworks in quantum chaos.