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  "slug": "differential-einthoven-inspired-readout-for-superconducting-qubit-measurement-th",
  "title": "Differential Einthoven‑Inspired Readout for Superconducting Qubit Measurement: Theory and Projected Fidelity Gains",
  "authors": [
    "Rowan Brad Quni-Gudzinas"
  ],
  "abstract": "Readout error dominates the overhead of quantum error correction in superconducting processors, limiting logical error rates and scaling prospects. Existing dispersive readout chains suffer from common‑mode disturbances such as amplifier drift, thermal fluctuations, and stray coupling, which add directly to the measured quadrature and reduce single‑shot fidelity. A gap remains in applying the well‑established differential amplification principle of electrocardiography to quantum measurement. We model a balanced, Einthoven‑style readout that measures a qubit simultaneously through two symmetric resonators (or feedlines) and processes the voltage difference. Starting from a linearized input‑output description, we derive closed‑form expressions for signal‑to‑noise ratio (SNR) and single‑shot fidelity for both single‑ended and differential configurations. Using representative noise parameters (common‑mode variance = 0.5 units², independent variance = 0.5 units²) the differential channel yields SNR = 1.0; in the limit of vanishing common‑mode noise (r→0) the analytic gain approaches √2≈1.414. Incorporating the two‑mode‑squeezing results of Ref. [...]",
  "abstract_markdown": "Readout error dominates the overhead of quantum error correction in superconducting processors, limiting logical error rates and scaling prospects. Existing dispersive readout chains suffer from common‑mode disturbances such as amplifier drift, thermal fluctuations, and stray coupling, which add directly to the measured quadrature and reduce single‑shot fidelity. A gap remains in applying the well‑established differential amplification principle of electrocardiography to quantum measurement. We model a balanced, Einthoven‑style readout that measures a qubit simultaneously through two symmetric resonators (or feedlines) and processes the voltage difference. Starting from a linearized input‑output description, we derive closed‑form expressions for signal‑to‑noise ratio (SNR) and single‑shot fidelity for both single‑ended and differential configurations. Using representative noise parameters (common‑mode variance = 0.5 units², independent variance = 0.5 units²) the differential channel yields SNR = 1.0; in the limit of vanishing common‑mode noise ($r\\to0$) the analytic gain approaches $\\sqrt{2}\\approx1.414$. Incorporating the two‑mode‑squeezing results of Ref. [...]",
  "date": "2026-10-18",
  "first_published": "2026-10-18",
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  "url": "https://papers.qnfo.org/papers/differential-einthoven-inspired-readout-for-superconducting-qubit-measurement-th",
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    "titles": [
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        "title": "Differential Einthoven‑Inspired Readout for Superconducting Qubit Measurement: Theory and Projected Fidelity Gains"
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        "description": "Readout error dominates the overhead of quantum error correction in superconducting processors, limiting logical error rates and scaling prospects. Existing dispersive readout chains suffer from common‑mode disturbances such as amplifier drift, thermal fluctuations, and stray coupling, which add directly to the measured quadrature and reduce single‑shot fidelity. A gap remains in applying the well‑established differential amplification principle of electrocardiography to quantum measurement. We model a balanced, Einthoven‑style readout that measures a qubit simultaneously through two symmetric resonators (or feedlines) and processes the voltage difference. Starting from a linearized input‑output description, we derive closed‑form expressions for signal‑to‑noise ratio (SNR) and single‑shot fidelity for both single‑ended and differential configurations. Using representative noise parameters (common‑mode variance = 0.5 units², independent variance = 0.5 units²) the differential channel yields SNR = 1.0; in the limit of vanishing common‑mode noise (r→0) the analytic gain approaches √2≈1.414. Incorporating the two‑mode‑squeezing results of Ref. [...]",
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