Fast rf-Reflectometry Readout of a Semiconductor Quantum Dot with Enhanced Gate Lever Arm

We characterize an in-situ superconducting quarter-wavelength coplanar stripline (CPS) microwave resonator directly coupled to a double quantum dot (DQD) in a Si/SiGe heterostructure [1]. This hybrid architecture enables high-bandwidth dispersive readout suitable for real-time feedback and future error correction protocols, advancing the scalability of Si/SiGe quantum dot qubits for quantum information processing [2.3]. We facilitate a strong dispersive signal by optimizing the DQD device's lever arm by design, through electrostatic simulations of the coupled Schrödinger-Poisson equations, using MaSQE [4], to extract an estimated lever arm to optimize. We demonstrate a signal-to-noise ratio (SNR) of unity with a 34.54 ns integration time, corresponding to a system bandwidth of 29 MHz and a charge sensitivity of of 0.000186 e per square root hertz. By analyzing the voltage power spectral density of the baseband in-phase (I) and quadrature (Q) signals, we estimate the effective charge noise in the system. We observe a 1/f noise spectrum up to approximately 10 kHz, likely due to charge fluctuation dynamics within the DQD.

[1] Tim J. Wilson et al. 2025, Fast and Sensitive Readout of a Semiconductor Quantum Dot Using an In-Situ Microwave Resonator with Enhanced Gate Lever Arm. arXiv.2510.00765

[2] Burkard et al. 2023, Semiconductor Spin Qubits. Rev. Mod. Phys. 95, 025003

[3] Vigneau et al. 2023, Probing quantum devices with radio-frequency reflectometry. Appl. Phys. Rev. 10, 021305

[4] Anderson et al. 2022, High-precision real-space simulation of electrostatically confined few-electron states. AIP Advances 12, 065123