Fast and high-fidelity dispersive readout of a spin qubit with squeezed microwave and resonator nonlinearity

Fast and high-fidelity qubit measurement is essential for quantum error correction in universal quantum computing. This study examines dispersive measurement of a spin in a semiconductor double quantum dot using a nonlinear microwave resonator. By employing displaced squeezed vacuum states, we achieve rapid, high-fidelity readout for silicon spin qubits. Our results show that modest squeezing and mild nonlinearity significantly enhance the signal-to-noise ratio (SNR) and the fidelity of qubit-state readout. By optimally adjusting the phases of squeezing and nonlinearity, we reduce readout time to sub-microsecond ranges. With current technology parameters (κ ≈ 2χ_s, χ_s/(2π) ≈ 0.15 MHz), utilizing a displaced squeezed vacuum state with 30 photons and a modest squeezing parameter r ≈ 0.6, along with a nonlinear microwave resonator charactered by a strength of λ ≈ − 1.2χ_s, a readout fidelity of 98% can be attained within a readout time of around 0.6 μs.