Interrupted Leakage-Tagged Readout Signatures in a Closed SU(3) Excursion fSim-GNS Pilot: A Low-Cost Operational Test of Transient Qutrit-Level Involvement
This short report presents a low-cost superconducting-qubit pilot study of interrupted leakage-tagged readout signatures in a q11--q12 fast-flux response branch. The target interpretation is a closed-excursion picture in which a prepared |11> proxy transiently couples to qutrit-level sectors such as |02> and/or |20> before returning near closure. The study does not perform qutrit-resolved tomography and does not directly observe |02> or |20>. Instead, it compares endpoint and interrupted leakage-tag protocols as operational tests of transient qutrit-level involvement. An endpoint-tag pilot at the 208 ns response branch produced only weak tag gain. Simulation-guided redesign moved the weak tag pulse to interrupted, mid-excursion timings. The first interrupted-tag pilot showed a stronger response at 96 ns, with p11 tag gain Δ≈0.063 and z≈2.92 while tag-only disturbance remained below the 8% guardrail. A focused 96 ns replication was weaker in p11 but retained a positive partner-channel component. An exploratory pooled analysis of the two 96 ns runs suggests a persistent partner-channel component, while p11 remains borderline. The appropriate conclusion is conservative: the response branch carries an operational interrupted-tag signature consistent with transient qutrit-level involvement, but direct observation of |02> and |20> remains future work.
This short report presents a low-cost superconducting-qubit pilot study of interrupted leakage-tagged readout signatures in a q11--q12 fast-flux response branch. The target interpretation is a closed-excursion picture in which a prepared |11> proxy transiently couples to qutrit-level sectors such as |02> and/or |20> before returning near closure. The study does not perform qutrit-resolved tomography and does not directly observe |02> or |20>. Instead, it compares endpoint and interrupted leakage-tag protocols as operational tests of transient qutrit-level involvement. An endpoint-tag pilot at the 208 ns response branch produced only weak tag gain. Simulation-guided redesign moved the weak tag pulse to interrupted, mid-excursion timings. The first interrupted-tag pilot showed a stronger response at 96 ns, with p11 tag gain Δ≈0.063 and z≈2.92 while tag-only disturbance remained below the 8% guardrail. A focused 96 ns replication was weaker in p11 but retained a positive partner-channel component. An exploratory pooled analysis of the two 96 ns runs suggests a persistent partner-channel component, while p11 remains borderline. The appropriate conclusion is conservative: the response branch carries an operational interrupted-tag signature consistent with transient qutrit-level involvement, but direct observation of |02> and |20> remains future work.
This technical note translates Temporal Interference String Theory (TIST) into concrete quantum-control protocols for superconducting qubits and qutrit-like leakage dynamics. Unlike the TIST White Paper, which introduces a broader synchronization-geometric research program, this note focuses on experimentally accessible quantities: readout-frame synchronization, geometric pulse response, leakage-tagged mapping, closed SU(3)-like excursions, and open-system density-matrix modeling. The central operational thesis is that a subset of noise, leakage, phase-response anomalies, and readout ambiguity can be modeled as incomplete synchronization between internal system phase-time and external control/readout time. This does not replace standard superconducting-qubit physics. Instead, it provides a complementary diagnostic layer for identifying synchronization windows, geometric response branches, and leakage-mediated return paths. The note defines measurable synchronization metrics, including phase-derived mismatch Δτ, synchronization quality Csync, co-rotating readout fidelity FCDVP, geometric curvature response CAPC, leakage-tag gain Gm, final leakage Lfinal, and open-system synchronization decay Γsync. It also outlines low-cost pilot experiments designed to distinguish geometric synchronization effects from ordinary pulse calibration, cross-talk, readout drift, and incoherent leakage. This document should be read as the operational quantum-control companion to TIST v0.2.1. Its goal is conservative: not to prove TIST as a fundamental theory, but to define a reproducible quantum-control test suite that can support, constrain, or falsify the TIST-QC interpretation.
Fast, accurate, and low-leakage qubit measurement is a key requirement for quantum error correction. Here, we demonstrate measurement of a superconducting transmon qubit with a total duration of 97(1) ns, defined as the time from the start of the measurement pulse until the measurement-induced error on a subsequent π-pulse operation falls below 10−4. By combining a large state-averaged resonator decay rate of κeff/2π = 30.8 MHz with a dispersive shift close to the optimal SNR-per-photon condition, we achieve an assignment error of 0.17(1)% using a 58-ns measurement pulse, with residual readout photons depleting passively in tens of nanoseconds without an active depletion pulse. Using a repeated-measurement sequence together with a leakage-sensitive measurement, we benchmark the measurement-induced state transitions, finding a per-measurement leakage rate of 2.7(2)×10−5, only twice the background rate and two orders of magnitude below the measurement-induced relaxation rate, which dominates the assignment error. Floquet simulations indicate that the multiphoton resonances present at the operating point are weakly coupled and traversed diabatically, without causing leakage. These results demonstrate that a large resonator decay rate, combined with a dispersive shift close to the optimal SNR-per-photon condition, can enable fast, high-fidelity, low-leakage dispersive readout at small qubit-resonator detuning.
Reset performance in superconducting qubits is often summarized by the population that remains at the end of the pulse. This is an important number, but it does not describe what happens during the reset itself. A protocol may reach a small final residual while keeping the qubit in a leakage state for a comparatively long part of the trajectory. In this work, we therefore use time-integrated leakage, together with the usual endpoint population, to study a multi-mode dissipative reset model under flux-frequency control. We examine finite thermal occupation, parameter sweeps, frequency disorder, an auxiliary-chain ablation, and a literature-based rate benchmark. At the representative ablation point, adding the auxiliary chain reduces Lf from 8.56 to 0.78 ns and shifts the sustained Pf less-than- 10-2 crossing from 39.5 to 9.8 ns. Interestingly, the configuration without the chain still reaches the smaller long-time residual. The two metrics can therefore favor different reset configurations. For the same 300 ns analysis window, an effective rate model built from the f-ket and e-ket decay rates reported by Zhou et al. gives Lf is 108.0 ns, while the complete simulated configuration gives 0.783 ns. We use this only as a kinetic reference and not as a reproduction of the experiment. In the wider set of simulations, thermal occupation is the main source of degradation, while the frequency disorder considered here has a much weaker effect. The results suggest that time-integrated leakage is a useful quantity to report alongside endpoint residuals, especially when reset is part of repeated quantum-error-correction cycles.
Active reset returns a superconducting qubit to its ground state: read it out, apply a π-pulse if it reads excited. The classical decision between the two takes time, and the qubit relaxes meanwhile. Salathé and co-workers tied this cost to the ratio of feedback latency to lifetime and expected the error to scale as one minus its exponential, and Ristè and co-workers had already written the reset error to first order as readout errors plus equilibration terms linear in the latency. This work makes that accounting exact at a fixed evaluation time. A transmon with T₁ = 50 μs is prepared in its excited state and read out by an ideal terminal projection followed by a classical confusion channel with symmetric assignment error P_AE. Under that instrument the ensemble-averaged residual population after one feedback cycle is an exact weighted sum of four deterministic Lindblad evolutions, conditioned on the projected and the reported outcome. The sum is evaluated in closed form, together with the critical latency τ_crit at which the residual exceeds its zero-latency value by a chosen budget, defined throughout as an absolute increase in excitation probability of 0.01, that is one percentage point. To leading order τ_crit is the budget times T₁ divided by the pulse-firing probability p_pulse, times a prefactor of 1.019 for the parameters considered here. Discarding that prefactor while retaining the division by p_pulse costs under 2%; the further simplification to budget times T₁ carries 3.4% to 7.3% error across P_AE = 1% to 5%. Because P_AE enters only through p_pulse, the budget is weakly sensitive to assignment error over the tested range for an initially excited qubit, giving 518 to 539 ns; the readout duration enters separately, through the observation window and the post-readout population. A critical latency exists only for budgets below the maximum excess attainable within that window. The four-branch representation is exact for the stated measurement model; the finite-pulse map used to evaluate it is approximate, and is replaced here by its exact affine propagator. The closed form agrees with a master-equation solver to 3.3×10⁻⁷ and is cross-checked against stochastic trajectories.
Abstract We study whether a fixed qutrit feature geometry built from classical time-series derivatives and residual variability supports compact readouts that remain meaningful across heterogeneous cohorts. The eight special-unitary-group SU(3) Gell-Mann coordinates are derived analytically as deterministic functions of the four classical inputs, making the representation's inductive structure explicit. We then separate representation, candidate readout subspace, fitted direction, target detectability, and predictive utility under participant-separated evaluation. Human Activities and Postural Transitions (HAPT) data repeatedly select the gauge-fixed sector {λ₆, λ₈}. On Daphnet freezing-of-gait data, this core reaches pooled area under the receiver operating characteristic curve (AUROC) 0.72572 with participant-cluster jackknife 95% interval [0.63792, 0.81352], close to 0.72872 for the full eight-coordinate qutrit representation (Q3). A prospectively frozen FoG-STAR lower-back test fails its empirical detectability screen: the best pre-specified model has AUROC 0.50977 [0.45615, 0.56339]. A post-hoc event-level audit using archived fold-specific thresholds finds high nominal event sensitivity but 4.06 false alarms per minute on Daphnet and 27.69 on FoG-STAR primary, excluding a practical detector interpretation. Local encoder perturbations do not rescue the failed primary transfer. Same-information classical interaction features match or exceed reconstructed Q3 on several external settings. Thus neither quantum advantage nor SU(3)-specific predictive gain is supported. The contribution is a falsification-oriented, gauge-aware framework for testing whether compact operator readouts survive cohort, sensor, and task shifts.
Frequency-multiplexed superconducting-qubit control requires more than carrier assignment: the RF budget of a shared source can perturb multi-qubit rotations through finite bandwidth, crest factor, clipping, quantization, jitter, spurs, compression, crosstalk, and leakage. We present an RF-budgeted frame-compilation and validation workflow that combines qubit-control identity (QID) records, a MATLAB/Simulink-based circuit-informed RFSoC source-chain model, QuTiP qutrit dynamics, and Qiskit-derived algorithm workloads. QID records encode qubit-specific computational and leakage transition frequencies, pulse parameters, and drive-scale calibration, while the RF-chain profile and effective crosstalk-coupling matrix are provided as separate compiler inputs. Candidate multitone RF frames are scheduled under RF-budget constraints, propagated through the RFSoC model, decoded into computational and leakage transition frames, and evaluated in QuTiP for rotation error, leakage-aware fidelity, computational-subspace survival, and transient leakage. The studies progress from single-qutrit pulse closure to pairwise coexistence, multitone RF-frame capacity, and Bernstein-Vazirani (BV) and QAOA microwave layers extracted from Qiskit circuits. The simulations show that longer pulses improve per-frame aggregation but do not necessarily minimize time-normalized layer cost; clustered frequency maps, larger rotations, and multitone leakage stacking tighten closure. Under the nominal RF budget, a Qiskit-derived 12-qubit BV -Y90 layer closes in three validated four-tone frames at 240 ns, while QAOA mixer partitions vary with rotation angle and pulse duration. All reported results are model-based, decoherence-free simulation diagnostics rather than measured hardware fidelities or wiring-reduction claims.