This record presents TA21 (Experimental Quadrature Extraction Protocol), part of the Q5 Transport Architecture Series developed under the Zero-Point Hypothesis framework. TA20 identified the three-part diagnostic signature for Q5 depth-mode leakage: monotone mode scaling, smooth-mode null, and phase-locked quadrature deviation. TA21 converts this control logic into a concrete operational protocol specifying preparation steps, measurement procedure, fitting procedure, and control experiments. The depth coordinate arising in the Q5 framework from the 320-slot transport graph structure does not have a direct laboratory counterpart. The protocol, therefore, works with a structural analog: depth modes of frequency n are simulated by inserting a phase modulator in one arm of a standard two-path interferometer and driving it with a structured phase profile equal to n times a fixed reference profile. The modulation frequency n plays the role of the depth-mode index, with n equal to zero giving a flat constant phase corresponding to the smooth gate-aligned mode, and increasing n giving increasing phase oscillation corresponding to higher depth modes. The protocol tests mode-dependent transport sensitivity rather than literal realization of the depth coordinate. The spectral scaling of leakage with modulation frequency is the object under test, not the geometric origin of that scaling. The measurement procedure scans the global inter-arm phase and records the interference intensity as a function of phase for each modulation frequency. The intensity pattern is fit to a quadrature form, extracting coefficients Aₙ and Bₙ. The deviation magnitude is then computed as the square root of the sum of squares of Aₙ minus one and Bₙ, providing a scalar observable that can be plotted against n. The TA20 signature is tested by checking three conditions. First, smooth-mode null: the deviation magnitude at n equal to zero should vanish or be negligible. Second, monotone scaling: the deviation magnitude should show a trend-level monotonic increase with n up to experimental uncertainty, with the stronger model-dependent form predicting scaling as eta times n squared. Third, phase-locked quadrature: the deviation must remain in the cosine-phi and sine-phi basis rather than appearing as random fringe drift, amplitude noise, or uncontrolled phase wandering. Three control experiments provide false-positive rejection. Power variation changes beam intensity without changing phase structure and should leave the deviation magnitude unchanged, ruling out intensity artifacts. Noise injection adds random phase noise and should reduce visibility without producing clean n-dependent scaling, ruling out noise-driven drift. Symmetric modulation applies identical phase modulation to both arms and should suppress the deviation to near zero, because the symmetric modulation cancels in interference. The symmetric modulation control is the strongest of the three because it directly tests whether asymmetry is essential to the signal, which matches the leakage architecture. The measurement machinery is standard: two-path interferometry and quadrature extraction are established experimental techniques. The interpretation is not standard and is classified separately. The mapping from phase modulation to depth-mode analog is a structural analogy, not a formal derivation. The TA18 through TA19 depth-leakage model is falsified at the protocol level if the deviation magnitude shows no n-dependence, if the deviation is random or phase-unlocked, or if the symmetric control fails to suppress the deviation. A positive result compatible with all three conditions does not constitute proof of the Q5 mechanism but constitutes a result consistent with it. The theorem chain progressively derives the structure of the effective transport generator \ Gₑff = PiY G PiY + K†BK \, from which observable phase, leakage, decoherence, and residual correction emerge as structural consequences of projected transport closure on Q5.
Craig Edwin Holdway (Mon,) studied this question.