{
  "id": "2401.03617",
  "version": "v1",
  "published": "2024-01-08T01:11:17.000Z",
  "updated": "2024-01-08T01:11:17.000Z",
  "title": "Fast and high-fidelity dispersive readout of a spin qubit via squeezing and resonator nonlinearity",
  "authors": [
    "Chon-Fai Kam",
    "Xuedong Hu"
  ],
  "comment": "14 pages, 4 figures, 1 table",
  "categories": [
    "cond-mat.mes-hall",
    "quant-ph"
  ],
  "abstract": "Fast and high-fidelity qubit measurement is crucial for achieving quantum error correction, a fundamental element in the development of universal quantum computing. For electron spin qubits, fast readout stands out as a major obstacle in the pursuit of error correction. In this work, we explore the dispersive measurement of an individual spin in a semiconductor double quantum dot coupled to a nonlinear microwave resonator. By utilizing displaced squeezed vacuum states, we achieve rapid and high-fidelity readout for semiconductor spin qubits. Our findings reveal that introducing modest squeezing and mild nonlinearity can significantly improve both the signal-to-noise ratio (SNR) and the fidelity of qubit-state readout. By properly marching the phases of squeezing, the nonlinear strength, and the local oscillator, the optimal readout time can be reduced to the sub-microsecond range. With current technology parameters ($\\kappa\\approx 2\\chi_s$, $\\chi_s\\approx 2\\pi\\times 0.15 \\:\\mbox{MHz}$), utilizing a displaced squeezed vacuum state with $30$ photons and a modest squeezing parameter $r\\approx 0.6$, along with a nonlinear microwave resonator charactered by a strength of $\\lambda\\approx -1.2 \\chi_s$, a readout fidelity of $98\\%$ can be attained within a readout time of around $0.6\\:\\mu\\mbox{s}$. Intriguing, by using a positive nonlinear strength of $\\lambda\\approx 1.2\\chi_s$, it is possible to achieve an SNR of approximately $6$ and a readout fidelity of $99.99\\%$ at a slightly later time, around $0.9\\:\\mu\\mbox{s}$, while maintaining all other parameters at the same settings.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2024-01-08T01:11:17.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "spin qubit",
      "high-fidelity dispersive readout",
      "displaced squeezed vacuum state",
      "resonator nonlinearity",
      "nonlinear microwave resonator"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 14,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}