We show that QFT (as well as QM) is not a complete physical theory. We constructed a classical statistical model inducing quantum field averages. The phase space consists of square integrable functions,
f(ϕ), of the classical bosonic field,
ϕ(x). We call our model prequantum classical statistical field-functional theory -- PCSFFT. The correspondence between classical averages given by PCSFFT and quantum field averages given by QFT is asymptotic. The QFT-average gives the main term in the expansion of the PCSFFT-average with respect to the small parameter
α -- dispersion of fluctuations of "vacuum field functionals.'' The Scrödinger equation of QFT is obtained as the Hamilton equation for functionals,
F(f), of classical field functions,
f(ϕ). The main experimental prediction of PCSFFT is that QFT gives only approximative statistical predictions that might be violated in future experiments.
Distinct monitoring or intervention schemes can produce different conditioned stochastic quantum trajectories while sharing the same unconditional (ensemble-averaged) dynamics. This is the essence of unravelings of a given Gorini-Kossakowski-Sudarshan-Lindblad (GKSL) master equation: any trajectory-ensemble average of a function that is linear in the conditional state is completely determined by the unconditional density matrix, whereas applying a nonlinear function before averaging can yield unraveling-dependent results beyond the average evolution. A paradigmatic example is resonance fluorescence, where direct photodetection (jump/Poisson) and homodyne or heterodyne detection (diffusive/Wiener) define inequivalent unravelings of the same GKSL dynamics. In earlier work, we showed that nonlinear trajectory averages can distinguish such unravelings, but observing the effect in that optical setting requires demanding experimental precision. Here we translate the same idea to a digital setting by introducing synthetic unravelings implemented as quantum circuits acting on one and two qubits. We design two unravelings - a projective measurement unraveling and a random-unitary "kick" unraveling - that share the same ensemble-averaged evolution while yielding different nonlinear conditional-state statistics. We implement the protocols on superconducting-qubit hardware provided by IBM Quantum to access trajectory-level information. We show that the variance across trajectories and the ensemble-averaged von Neumann entropy distinguish the unravelings in both theory and experiment, while the unconditional state and the ensemble-averaged expectation values that are linear in the state remain identical. Our results provide an accessible demonstration that quantum trajectories encode information about measurement backaction beyond what is fixed by the unconditional dynamics.
Defects at the interfaces in the Josephson junction (JJ) are well known as a primary source of decoherence in superconducting quantum devices, indicating the necessity of elucidating defect reaction mechanisms to improve qubit performance. However, their micromechanism remains elusive. Here, we reveal the micromechanism of defects affecting the transport properties by building interfacial defective JJ device models combined with density functional theory (DFT) and nonequilibrium Green’s function (NEGF) approach. By comparing the conductance values of various interface classification models with oxygen vacancies (OVs), we find that the aluminum-rich (Al-rich) interface exhibits the smallest conductance variation, resulting in less qubit frequency fluctuations, and this can be further explained by changes in the electrostatic potential relative to the average barrier height. More importantly, the Al-rich interface demonstrates the highest stability. This work provides a theoretical basis and optimization direction for superconducting quantum chip fabrication.