AIDT 온디바이스 STEM 방사광 X선 극저온 플럭소늄(Fluxonium) 초전도 큐비트 반양자자속(0.5 Phi_0) 바이어스 고속 서보 제어기

using System;
using System.Runtime.CompilerServices;

namespace ZeliDesk.Stem.FluxoniumQubit
{
    /// <summary>
    /// 플럭소늄 분산 판독 텔레메트리 상태
    /// </summary>
    public readonly ref struct FluxoniumTelemetryState
    {
        public readonly double ReadoutResonatorShiftKhz; // 판독 공진기 주파수 천이 [kHz]
        public readonly double InjectedFluxPhi0;         // 현재 추정 인가 자속 [Phi_0]
        public readonly double CryoStageTempMilliKelvin; // 냉각단 온도 [mK]
        public readonly double ReadoutSnrDb;             // 판독 신호 대 잡음비 [dB]

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public FluxoniumTelemetryState(double shift, double flux, double temp, double snr)
        {
            ReadoutResonatorShiftKhz = shift;
            InjectedFluxPhi0 = flux;
            CryoStageTempMilliKelvin = temp;
            ReadoutSnrDb = snr;
        }
    }

    /// <summary>
    /// 플럭소늄 자속 바이어스 서보 명령
    /// </summary>
    public readonly ref struct FluxoniumServoCommand
    {
        public readonly double BiasCurrentMicroAmps;     // 초전도 코일 전류 지령 [uA]
        public readonly double FluxDriftMicroPhi0;       // 잔여 자속 표류 [u-Phi_0]
        public readonly double EstimatedQubitCoherenceUs;// 추정 T2 결맞음 시간 [us]
        public readonly bool AtSweetSpot;                // 0.5 Phi_0 스위트스팟 잠금 여부

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public FluxoniumServoCommand(double current, double drift, double t2, bool sweet)
        {
            BiasCurrentMicroAmps = current;
            FluxDriftMicroPhi0 = drift;
            EstimatedQubitCoherenceUs = t2;
            AtSweetSpot = sweet;
        }
    }

    /// <summary>
    /// 10,000Hz 주기 플럭소늄 반양자자속 바이어스 서보 엔진
    /// </summary>
    public ref struct FluxoniumFluxBiasServoEngine
    {
        private const double IdealSweetSpotPhi0 = 0.500000;
        private const double CoilSensitivityMicroPhi0PerMicroAmp = 1250.0;

        private double _accumulatedCurrentUa;
        private double _prevFluxError;

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public FluxoniumServoCommand CalculateServoControl(
            in FluxoniumTelemetryState state, double dtSeconds)
        {
            double fluxErrorPhi0 = state.InjectedFluxPhi0 - IdealSweetSpotPhi0;
            double fluxErrorMicroPhi0 = fluxErrorPhi0 * 1e6;

            double errorDiff = (dtSeconds > 1e-9) ? (fluxErrorMicroPhi0 - _prevFluxError) / dtSeconds : 0.0;
            _prevFluxError = fluxErrorMicroPhi0;

            // PI 폐루프 전류 제어
            _accumulatedCurrentUa -= (0.25 * fluxErrorMicroPhi0 / CoilSensitivityMicroPhi0PerMicroAmp) * dtSeconds;
            _accumulatedCurrentUa = Math.Clamp(_accumulatedCurrentUa, -50.0, 50.0);

            double commandCurrentUa = 400.0 + _accumulatedCurrentUa - (0.05 * fluxErrorMicroPhi0 / CoilSensitivityMicroPhi0PerMicroAmp);

            // 잔여 오차 및 결맞음 시간 T2 추정
            double residualDriftMicroPhi0 = Math.Abs(fluxErrorMicroPhi0);
            bool atSweet = residualDriftMicroPhi0 < 5.0; // 5 uPhi_0 이내

            // T2 추정: 잔여 자속 잡음 반비례 모델
            double t2Us = atSweet ? 1200.0 / (1.0 + 0.08 * residualDriftMicroPhi0) : 45.0;

            return new FluxoniumServoCommand(commandCurrentUa, residualDriftMicroPhi0, t2Us, atSweet);
        }
    }
}