We report evidence consistent with non-exponential decoherence in superconducting transmon qubits. Ramsey interferometry data from five qubits on IBM Quantum hardware show that a stretched-exponential model f(t) = exp(-(t/T2 ) beta) fits the observed decay better than the standard exponential (beta = 1). On our primary qubit (Q0), we measure beta = 2.06 with R2 = 0.9964 versus R2 = 0.9586 for the exponential, with Bayesian Information Criterion favoring the stretched model by 46 units. While non-exponential decay in superconducting qubits has been previously observed in the context of 1/f noise [4], the present work provides a systematic multi-qubit characterization with a fully reproducible protocol and proposes a falsifiable geometry-dependent prediction (RAB != 1) that distinguishes this framework from collapse-model alternatives.
We report evidence consistent with non-exponential decoherence in superconducting transmon qubits. Ramsey interferometry data from five qubits on IBM Quantum hardware show that a stretched-exponential model f(t) = exp(-(t/T2 ) beta) fits the observed decay better than the standard exponential (beta = 1). On our primary qubit (Q0), we measure beta = 2.06 with R2 = 0.9964 versus R2 = 0.9586 for the exponential, with Bayesian Information Criterion favoring the stretched model by 46 units. While non-exponential decay in superconducting qubits has been previously observed in the context of 1/f noise [4], the present work provides a systematic multi-qubit characterization with a fully reproducible protocol and proposes a falsifiable geometry-dependent prediction (RAB != 1) that distinguishes this framework from collapse-model alternatives.
Quantum decoherence is universally assumed to follow Markovian (simple exponential) dynamics in analog quantum processors, yet this assumption has never been experimentally tested. We report the first measurement of the stretched exponential parameter β characterizing coherence decay on an analog quantum platform. Using QuEra's Aquila Rydberg atom processor, we measure β = 3.52 ± 1.05 across three system sizes (N=4, 6, 8 atoms), significantly exceeding values observed on gate-based superconducting platforms (β = 1.27 ± 0.25, IBM Quantum). This 2.8-fold difference demonstrates fundamental platform-dependent variations in decoherence mechanisms. The observed super-exponential decay (β > 2.5) indicates strong non-Markovian effects in neutral atom systems, contradicting the standard Markovian assumption. We observe a trend toward larger β values with increasing system size, suggesting many-body correlation effects. These results establish β as a platform-dependent observable and open new directions for characterizing decoherence in quantum processors.
This study presents a reanalysis of high-precision neutron interferometry data from the Institut Laue-Langevin (ILL), revealing a significant deviation from the traditionally expected exponential decoherence. The interference visibility exhibits a stretched-exponential decay, characterized by V(t)=V0exp[−(t/τcoh)1+ε] with a measured ε=0.18±0.08, in agreement with the theoretical prediction of ε=0.23±0.02. These results provide the first experimental support for the Quantum Phase Interpretation (QPI), in which quantum systems evolve through dynamical phases rather than static states. The phase-based model achieves a substantially better fit than conventional collapse models, with a 3.9-fold improvement in χ2, and aligns closely with the theoretical framework of nonlinear phase diffusion. The study has significant implications for the foundations of quantum mechanics, offering new insights into decoherence mechanisms, the measurement problem, and the emergence of classicality from quantum phase dynamics. Proposed future experiments aim to test phase evolution across different quantum systems, including photons, neutrons, and quantum dots. Keywords: Quantum Phase, Neutron Interferometry, Decoherence, Non-Exponential Decay, Quantum Foundations, Phase Dynamics, Measurement Problem
This publication presents a straightforward experimental study measuring the energy-relaxation time, or T1, of a superconducting qubit on IBM Quantum hardware. It explains the basic idea behind the test, preparing the qubit in the excited state, letting it sit for different delay times, and measuring how quickly it decays back toward the ground state, then fits the results to an exponential decay model that accounts for measurement imperfections. Using the ibm_torino backend on qubit Q0, the paper reports a measured T1 of about 132 microseconds, based on a single sweep of 25 delay values with 4096 shots per point. Along with the result, the publication includes the theoretical model, experimental setup, raw decay data, and discussion of limitations such as noise, drift, and fit-quality concerns, making it both a concise report of the measurement and a reproducible example for readers interested in quantum hardware characterization.
Building upon our prior work [1], we present a unified stochastic drift model (SdM) for superconducting charge qubits based on memory multi-fractional Brownian motion (mmFBM). The classical sector employs a time-dependent Hurst exponent H(t) and adaptive memory kernel K(t,s), capturing non-stationary 1/f^beta noise and long-range temporal correlations inaccessible to conventional models. The quantum extension is formulated via a time-dependent Caldeira--Leggett environment with spectral density J(omega;t) = eta(t) omega_c^{1-s(t)} omega^{s(t)} exp(-omega/omega_c), where s(t) = 2H(t)-1, consistently reproducing beta(t) = 2H(t)-1.
Four central results emerge: (1) relaxation and noise amplitudes act independently on energy decay; (2) time-varying H(t) matches experimental 1/f spectra more accurately than any constant exponent; (3) adaptive kernel dynamics preserve correlations without artificial damping; and (4) simulations predict coherence times (T1 ~ 5.00 x 10^6 ns, T2 ~ 4.18 x 10^5 ns) consistent with theory when charge noise dominates. The qubit exhibits stretched-exponential Ramsey and echo decay, non-Markovian dephasing, and a temperature-driven quantum-to-classical crossover. We derive the effective time-local Lindblad master equation, establish the classical mmFBM limit at high temperatures, and provide experimentally testable scaling relations. The non-exponential decay patterns reveal fundamental limitations of Markovian approaches, and the framework guides the design of noise-resilient qubit architectures.
TSR-Q-1 presents a preregistered and falsifiable experimental protocol designed to test for structured late-time coherence residuals in superconducting transmon qubits. The protocol does not treat generic recoherence, non-exponential decay, or non-Markovian behavior as evidence for the proposed framework, since such phenomena may arise from conventional open-system mechanisms. Instead, it targets a specific normalized temporal scaling law, tₙ/T₂ = nᵏ, with the preregistered theoretical value k* = 1.4706, corresponding to the first two target locations t₂/T₂ = 2.7714 and t₃/T₂ = 5.0310. If the associated amplitude-scaling hypothesis is retained, the predicted ratio is A₃/A₂ ≈ 0.551. The accompanying computational validation package develops the analysis pipeline through five stages: preliminary signal injection, blind null testing, blind injection-recovery, multi-qubit global-k inference, and sensitivity mapping. The synthetic null models include stretched-exponential decay, 1/f^α correlated noise, random-telegraph/TLS-like contributions, slow drift, white noise, and device-to-device variability. These simulations validate the detectability, specificity, and sensitivity of the proposed analysis procedure under the tested synthetic noise families. They do not constitute experimental evidence for the existence of the predicted physical effect. The next stage is a preregistered hardware implementation using superconducting qubits, with device-specific null calibration, blind analysis, systematic controls, held-out replication, and, ultimately, independent experimental replication.
Crosstalk between qubits fundamentally limits the scalability of quantum processors, necessitating physics-based models that can handle the complexity of large qubit arrays. Here, we develop a comprehensive theoretical and experimental framework that captures residual interactions between both adjacent and non-adjacent qubits in fixed-frequency transmon lattices. The model integrates the combined effects of exponential localization in banded capacitance matrices, suppression of virtual couplings through detuning products across intermediate modes, and evanescent decay of below-cutoff electromagnetic fields, yielding predictive scaling relations for coupling strength as a function of spatial separation and spectral detuning. Experimental characterization of a 4×4 superconducting-qubit lattice with inductive shunt pillars reveals exponential spatial decay and frequency-dependent suppression consistent with theoretical predictions, achieving quantitative agreement for all nearest-neighbor couplings across the \qtyrange[range-phrase = --, range-units = single]{4}{6}{\giga\hertz} operating range. Our results show that standard dispersive Hamiltonian approximations systematically overestimate long-range coupling when spatial and spectral dependencies are neglected; these errors propagate into circuit simulation and design strategies. Our framework provides design guidance for crosstalk mitigation in larger-scale quantum processors under realistic fabrication constraints, addressing a bottleneck in scalability.