Near-ultrastrong nonlinear light-matter coupling in superconducting circuits.
basic_science · Level V
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- Record sourced from PubMed, PMID 40307215.
- Also identified by DOI 10.1038/s41467-025-59152-z and PMC identifier 12043914.
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Abstract
Light-matter interaction between an atom and an electromagnetic resonator is ubiquitous in quantum technologies. Although linear light-matter coupling <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>g</mi> <msub> <mrow> <mover><mrow><mi>σ</mi></mrow> <mrow><mo>̂</mo></mrow> </mover> </mrow> <mrow><mi>x</mi></mrow> </msub> <mrow><mo>(</mo> <mrow> <mover><mrow><mi>a</mi></mrow> <mrow><mo>̂</mo></mrow> </mover> <mo>+</mo> <msup> <mrow> <mover><mrow><mi>a</mi></mrow> <mrow><mo>̂</mo></mrow> </mover> </mrow> <mrow><mo>†</mo></mrow> </msup> </mrow> <mo>)</mo></mrow> </math> can reach the ultrastrong regime g/ω > 10<sup>-1</sup>, nonlinear light-matter coupling <math xmlns="http://www.w3.org/1998/Math/MathML"> <mfrac><mrow><mi>χ</mi></mrow> <mrow><mn>2</mn></mrow> </mfrac> <msub> <mrow> <mover><mrow><mi>σ</mi></mrow> <mrow><mo>̂</mo></mrow> </mover> </mrow> <mrow><mi>z</mi></mrow> </msub> <msup> <mrow> <mover><mrow><mi>a</mi></mrow> <mrow><mo>̂</mo></mrow> </mover> </mrow> <mrow><mo>†</mo></mrow> </msup> <mover><mrow><mi>a</mi></mrow> <mrow><mo>̂</mo></mrow> </mover> </math> is typically perturbative and limited to χ/ω < 10<sup>-2</sup>. Nonlinear coupling has the advantage of commuting with the atomic <math xmlns="http://www.w3.org/1998/Math/MathML"> <msub> <mrow> <mover><mrow><mi>σ</mi></mrow> <mrow><mo>̂</mo></mrow> </mover> </mrow> <mrow><mi>z</mi></mrow> </msub> </math> and photonic <math xmlns="http://www.w3.org/1998/Math/MathML"> <msup> <mrow> <mover><mrow><mi>a</mi></mrow> <mrow><mo>̂</mo></mrow> </mover> </mrow> <mrow><mo>†</mo></mrow> </msup> <mover><mrow><mi>a</mi></mrow> <mrow><mo>̂</mo></mrow> </mover> </math> Hamiltonian, allowing for fundamental operations such as quantum-non-demolition measurement. Here, we use a superconducting circuit to demonstrate the experimental realization of near-ultrastrong χ/ω = (4.852 ± 0.006) × 10<sup>-2</sup>. We also show signatures of light-light nonlinear coupling ( <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>χ</mi> <msup> <mrow> <mover><mrow><mi>a</mi></mrow> <mrow><mo>̂</mo></mrow> </mover> </mrow> <mrow><mo>†</mo></mrow> </msup> <mover><mrow><mi>a</mi></mrow> <mrow><mo>̂</mo></mrow> </mover> <msup> <mrow> <mover><mrow><mi>b</mi></mrow> <mrow><mo>̂</mo></mrow> </mover> </mrow> <mrow><mo>†</mo></mrow> </msup> <mover><mrow><mi>b</mi></mrow> <mrow><mo>̂</mo></mrow> </mover> </math> ) and χ/2π = 580.3 ± 0.4 MHz matter-matter nonlinear coupling ( <math xmlns="http://www.w3.org/1998/Math/MathML"> <mfrac><mrow><mi>χ</mi></mrow> <mrow><mn>4</mn></mrow> </mfrac> <msub> <mrow> <mover><mrow><mi>σ</mi></mrow> <mrow><mo>̂</mo></mrow> </mover> </mrow> <mrow><mi>z</mi> <mo>,</mo> <mi>a</mi></mrow> </msub> <msub> <mrow> <mover><mrow><mi>σ</mi></mrow> <mrow><mo>̂</mo></mrow> </mover> </mrow> <mrow><mi>z</mi> <mo>,</mo> <mi>b</mi></mrow> </msub> </math> ), representing the largest reported ZZ interaction between two coherent qubits. Such advances in the nonlinear coupling strength of light, matter modes enable new physical regimes and could lead to orders of magnitude faster qubit readout and gates.