Discriminating Thomas–Wigner from Pancharatnam–Berry Rotations in Sequential Weak Qubit Measurements: A Variable-Visibility Protocol
Bharath Srivats
Abstract
The Fisher–Lorentz identity I(V) = γ²(V) = 1/(1−V²) for binary quantum measurements predicts that sequential non-collinear weak measurements on a qubit accumulate a Thomas–Wigner (TW) rotation with a specific, visibility-dependent closed form. This prediction is numerically distinct from the Pancharatnam–Berry (PB) geometric phase that governs the same measurement cycle under the standard pure-state geometric-phase interpretation. This paper presents a pre-registered experimental protocol that discriminates between the two predictions on existing superconducting, trapped-ion, and neutral-atom platforms by sweeping the measurement visibility V ∈ [0.3, 0.99]. For the octant spherical triangle ẑ → x̂ → ŷ → ẑ, the PB prediction is Ω_PB = 45° (fixed by the enclosed solid angle of π/2 sr), while Ω_TW varies from 2.70° at V = 0.30 to 73.94° at V = 0.99, crossing the PB baseline at V_× ≈ 0.9102. The signed discrepancy Ω_TW − Ω_PB ranges from −42° to +29° across the sweep and provides two independent discrimination landmarks: a monotonic V-dependence and a sign-flipping crossing point. Shot counts, tomographic precision, readout fidelity, and systematic-error budgets sufficient for 3σ discrimination are specified per platform (≈45k shots total for pure initial state, ≈180k for mixed-state preparation at |r| ≈ 0.5). The protocol requires no new hardware. A successful run on any reasonable-fidelity qubit platform (IBM, Google, Rigetti, OQC, IQM transmons; Quantinuum or IonQ trapped ions; QuEra, Atom Computing, or Pasqal Rydberg arrays) either confirms a central prediction of the Fisher–Lorentz framework or falsifies it at 3σ. This is a methods paper: its purpose is to enable the experiment, not to re-establish the theory. Relation to companion preprints — This paper operationalises predictions derived in the Fisher–Lorentz framework developed in Srivats (2026), Fisher information is the squared Lorentz factor: why the qubit is special[10.5281/zenodo.19363449] and Srivats (2026), From measurement to reality: I(V) = γ²(V) and the geometry of binary distinction [10.5281/zenodo.19486140]. The SL(2,ℂ) ≅ Spin⁺(1,3) boost-composition structure on monitored qubits is established independently by Burns, Greenfield, and Dressel (Quantum Stud.: Math. Found. 13, art. 10, 2026); the present work extracts and pre-registers a specific crossing-point prediction (V_× ≈ 0.9102) as an operational TW/PB discriminator.