Junction readout without flux loops or parasitic modes

Dispersive readout—the standard technique for measuring superconducting qubits—has been shown to suffer from limitations due to multiphoton qubit–resonator processes that emerge even at moderate drive powers. Recently, an alternative approach known as junction readout has demonstrated that these multiphoton processes can be suppressed by introducing a nonlinear coupling between the qubit and resonator via a Josephson junction [1,2].

However, existing junction readout implementations often result in either a large flux loop or introduce unwanted low-frequency modes stemming from the nonlinear coupling. In this talk, we present a novel junction readout architecture that overcomes both of these challenges while maintaining performance comparable to the original design. Furthermore, we show that junction readout achieves exceptional performance in the large-detuning regime, free from the limitations that affect high-detuning dispersive readout [3].

[1] A. A. Chapple, O. Benhayoune-Khadraoui et al., arXiv:2501.09010

[2] C. Wang, F. Liu et al., Phys. Rev. Lett. 135, 060803

[3] P. Kurilovich, T. Connolly et al., arXiv:2501.09161