Controllable microwave three-wave mixing via a single three-level superconducting quantum circuit.

Area of Science:

• Quantum Optics
• Superconducting Circuits
• Nonlinear Optics

Background:

• Second-order nonlinear optical processes are forbidden in atomic systems by electric-dipole selection rules.
• Superconducting quantum circuits offer a novel platform for exploring quantum phenomena.
• Breaking inversion symmetry is key to enabling these nonlinear processes.

Purpose of the Study:

• To demonstrate second-order nonlinear processes in a superconducting quantum circuit.
• To show controllable frequency generation in the microwave regime.
• To utilize a single three-level superconducting flux quantum circuit (SFQC).

Main Methods:

• Breaking the inversion symmetry of the potential energy in an SFQC by adjusting applied magnetic flux.
• Utilizing a three-level SFQC to facilitate nonlinear processes.
• Operating in the microwave regime for frequency generation.

Main Results:

• Successfully demonstrated second-order nonlinear processes, including sum-frequency and difference-frequency generation, in an SFQC.
• Achieved controllable frequency tunability: ~17 GHz for sum-frequency and ~42 GHz or ~26 GHz for difference-frequency generation.
• Showcased the generation of second harmonics.

Conclusions:

• Second-order nonlinear processes can be achieved in superconducting artificial atoms by breaking inversion symmetry.
• SFQCs provide a tunable and controllable platform for microwave frequency generation.
• The proposed method offers a simple approach compatible with current experimental capabilities in SFQCs.