Complex-Time i-Phase as a Physical Degree of Freedom: Operational Evidence from Event-Additive Rotations in Dynamic Quantum Circuits

Abstract Complex-Time (CT) theory posits that physical time is not exhausted by a single real parameter t, but includes an internal rotation phase φ such that the time coordinate is τ = t + iφ. In this ontology, φ is not a mere mathematical artifact of complex amplitudes: it is a physical degree of freedom that mediates a rotation between two logically distinct time aspects—future-pending (fp) time that retains unrealized alternatives, and past-fixed (pf) time that corresponds to realized events and stable records. Dynamic quantum circuits with mid-circuit measurement (MCM) are an unusually direct laboratory for CT because they contain repeated, addressable fp→pf conversion events *inside a single circuit*.Here we analyze IBM superconducting quantum-processor data and show that the target-qubit equatorial coherence z ≡ ⟨σx⟩ + i⟨σy⟩ undergoes a deterministic complex rotation whose angle is set primarily by the number M of spectator mid-circuit measurements. In Dataset A (4096 shots; 5 repeats), the complex ratio w(M) ≡ z_MEAS(M)/z_DELAY(M) displays an event-additive phase shift Δθ_eff(M) = arg w(M) that grows from ≈ 0 at M = 0–1 to Δθ_eff(M=8) ≈ 2.279 rad, with an average increment of δ ≈ 0.323 rad per added measurement. In Dataset B (1024 shots), inserting a virtual-Z compensation Rz(comp×M) on the target yields linear response d(Δθ_eff)/d(comp) ≈ M and demonstrates coherent controllability of the rotation.To probe whether the effect is reducible to schedule-level artifacts alone, Dataset C (CT3 Layer3) uses identical classical control-flow (if-structure) while changing only the spectator’s internal phase coherence: mode A forces |+⟩ before each mid-measurement, whereas mode B allows a |+⟩/|−⟩ mixture to accumulate. A small but systematic phase difference Δθ_AB(M) = θ_A(M) − θ_B(M) emerges (≈ 0.06 rad at M = 4–8) alongside a large change in spectator ⟨σx⟩, consistent with an operational coupling between the driven phase rotation and an internal i-phase degree of freedom.We interpret these results as operational evidence that an i-axis phase coordinate is physically actionable: it can be incremented by pf-creating events and steered by coherent frame updates. This provides a concrete, hardware-grounded route for testing CT claims about the physical reality of the imaginary-time phase. Keywords: complex time; τ = t + iφ; i-phase; past-fixed / future-pending; dynamic circuits; mid-circuit measurement; complex-plane diagnostics; virtual-Z compensation.