Near-ultrastrong nonlinear light-matter coupling in superconducting circuits.

Area of Science:

• Quantum optics
• Superconducting circuits
• Quantum information science

Background:

• Light-matter interaction is fundamental to quantum technologies.
• Linear coupling can reach ultrastrong regimes, but nonlinear coupling is typically weak.
• Nonlinear coupling offers advantages like quantum non-demolition measurements.

Purpose of the Study:

• To experimentally realize near-ultrastrong nonlinear light-matter coupling.
• To explore signatures of light-light and matter-matter nonlinear coupling.
• To advance quantum technologies through enhanced nonlinear coupling.

Main Methods:

• Utilized a superconducting circuit to engineer light-matter interaction.
• Achieved a nonlinear coupling strength of χ/ω = (4.852 ± 0.006) × 10⁻².
• Demonstrated significant ZZ interaction between two coherent qubits.

Main Results:

• Experimental realization of near-ultrastrong nonlinear light-matter coupling.
• Observed signatures of light-light nonlinear coupling.
• Achieved the largest reported ZZ interaction (580.3 ± 0.4 MHz) between two coherent qubits.

Conclusions:

• Advances in nonlinear coupling strength open new physical regimes for quantum technologies.
• Enhanced nonlinear coupling could lead to significantly faster qubit readout and gates.
• This work paves the way for novel quantum computing and sensing applications.