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arXiv:2608.21435

Complex-Time Parametrization of Evanescent Tunneling and Transmission Delay in non-Hermitian Scattering

Iulia-Maria Daia

quant-phgr-qcmath-phSubmitted Aug 17, 2026• Announced Aug 19, 2026• 0 citations
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Abstract

The quantum tunneling process is a fundamental concept that presents the unconventional nature of quantum dynamics. The main anomaly of this effect revolves around the choice of imposing the classical 4-momentum to become imaginary during the barrier traversal. This paper addresses this paradox by introducing a complex-time parametrization, which uses a complex temporal coordinate, $τ= t + iκ$. Here, the real axis $(t)$ represents standard thermodynamic time, while the imaginary axis $(iκ)$ is correlated to spatial evanescence. We demonstrate that evaluating this extended complex-time framework yields a hyperbolic section of the causal lightcone, proving that the traversal is strictly bounded by the speed of light and preserves causal disconnection. Applied to quantum tunneling, we resolve the anomaly of imaginary momentum through a continuous geometric signature flip of the effective complex-time momentum norm from a timelike to a spacelike state. This theoretical model finds a physically phenomenological analogy in microwave scattering experiments using open, non-Hermitian systems, which link complex transmission time delay to spatial wave decay.

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39 pages, 6 figures

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The quantum tunneling process is a fundamental concept that presents the unconventional nature of quantum dynamics. The main anomaly of this effect revolves around the choice of imposing the classical 4-momentum to become imaginary during the barrier traversal. This paper addresses this paradox by introducing a complex-time parametrization, which uses a complex temporal coordinate, τ=t+iκτ= t + iκτ=t+iκ. Here, the real axis (t)(t)(t) represents standard thermodynamic time, while the imaginary axis (iκ)(iκ)(iκ) is correlated to spatial evanescence. We demonstrate that evaluating this extended complex-time framework yields a hyperbolic section of the causal lightcone, proving that the traversal is strictly bounded by the speed of light and preserves causal disconnection. Applied to quantum tunneling, we resolve the anomaly of imaginary momentum through a continuous geometric signature flip of the effective complex-time momentum norm from a timelike to a spacelike state. This theoretical model finds a physically phenomenological analogy in microwave scattering experiments using open, non-Hermitian systems, which link complex transmission time delay to spatial wave decay.
We develop a geometric framework in which physical time is represented as a complex variable T=t−iτ. The imaginary component τ encodes the attenuation of coherence, while the real component t retains its usual causal role. Motivated by recent delayed-choice implementations [1–4], we show that the experimental configuration acts as an internal rotation θ of the complex time, modifying the imaginary-time difference between interferometric paths and therefore the visibility. This mechanism alters coherence without affecting causal evolution in t and does not require retrocausality. The model remains fully compatible with standard quantum mechanics, preserving unitary evolution, the Born rule, and completely positive trace-preserving maps. It provides a minimal geometric reparametrisation of the dynamical phase and yields experimentally testable predictions for visibility and temporal correlations.
The scattering matrix S linearly relates the vector of incoming waves to outgoing wave excitations, and contains an enormous amount of information about the scattering system and its connections to the scattering channels. Time delay is one way to extract information from S, and the transmission time delay τ_{T} is a complex (even for Hermitian systems with unitary scattering matrices) measure of how long a wave excitation lingers before being transmitted. The real part of τ_{T} is a well-studied quantity, but the imaginary part of τ_{T} has not been systematically examined experimentally, and theoretical predictions for its behavior have not been tested. Here we experimentally test the predictions of Asano et al. [Nat. Commun. 7, 13488 (2016)NCAOBW2041-172310.1038/ncomms13488] for the imaginary part of transmission time delay in a nonunitary scattering system. We utilize Gaussian time-domain pulses scattering from a two-port microwave graph supporting a series of well-isolated absorptive modes to show that the carrier frequency of the pulses is changed in the scattering process by an amount in agreement with the imaginary part of the independently determined complex transmission time delay, Im[τ_{T}], from frequency-domain measurements of the subunitary S matrix. Our results also generalize and extend those of Asano et al., establishing a means to predict pulse propagation properties of non-Hermitian systems over a broad range of conditions.
We discuss some aspects of the time picture of tunneling for open quantum systems described by non-Hermitian (NH) Hamiltonians. The concept of sojourn time for such systems is introduced in the framework of the biorthonormal formalism. Due to the various definitions of probability density in the non-Hermitian case, we get three different sojourn times, two real and one complex. We consider as model of a dissipative NH system the complex, generalized parametric oscillator, for which we derive the exact expressions of the three sojourn times in terms of the Wei-Norman characteristic functions entering the non-unitary evolution operators. The special case of the inverted Caldirola-Kanai oscillator with complex friction parameter is investigated for an initial extended wavepacket. We also discuss the Landau-Zener-like transitions of the NH parametric oscillator, i.e. the dissipative tunneling through a dynamical barrier due to the perturbative effect of the damping.
The wave-packet simulation (WPS) method for calculating the time a tunneling particle spends inside a one-dimensional potential barrier is reexamined using the Feynman path-integral technique. Following earlier work by Sokolovski and Baskin [Phys. Rev. A 36, 4604 (1987)], the tunneling (or traversal) time tpackT{\mathit{t}}_{\mathrm{pack}}^{\mathit{T}}tpackT​ is defined as a matrix element of a classical nonlocal functional between two states that represent the initial and transmitted wave packets. These states do not lie on the same orbit in Hilbert space; as a result, tpackT{\mathit{t}}_{\mathrm{pack}}^{\mathit{T}}tpackT​ is complex-valued. It is shown that RetpackT{\mathit{t}}_{\mathrm{pack}}^{\mathit{T}}tpackT​ reduces to the standard WPS result, tphaseT{\mathit{t}}_{\mathrm{phase}}^{\mathit{T}}tphaseT​, for conditions similar to those employed in the conventional WPS analysis. Similarly, ImtpackT{\mathit{t}}_{\mathrm{pack}}^{\mathit{T}}tpackT​ is shown to contain information about the energy dependence of the transmission probability. Under semiclassical conditions, ImtpackT{\mathit{t}}_{\mathrm{pack}}^{\mathit{T}}tpackT​ reduces to the well-known Wentzel-Kramers-Brillouin expression for the tunneling time. It is shown there are different definitions for the traversal time of a classical moving object, whose size is comparable to the width of the region of interest. In the quantum case, these different definitions correspond to different ways of analyzing the WPS experiment. The path-integral approach demonstrates that the tunneling-time problem is one of understanding the physical significance of complex-valued off-orbit matrix elements of an operator or functional. The physical content of complex-valued tunneling times is discussed. It is emphasized that the use of complex tunneling times includes real-time approaches as a special case. Nevertheless, there is a limitation in the description of tunneling experiments using tunneling times, whether real or complex. The path-integral approach does not supply a universal traversal time, analogous to a classical time, that can be used in quantum situations. It is demonstrated that the often expressed hope of finding a well-defined and universal real tunneling time is erroneous.
Abstract This paper extends the framework developed in Part I: Complex-Time Geometry and Phase Symmetry by examining the ontological origin and physical meaning of the imaginary rotation eiθeiθ that sustains temporal continuity.While Part I defined time as an intrinsic complex-phase rotation linking quantum mechanics and relativity, the present work investigates what the imaginary component ii itself represents in the emergence of temporal direction and measurement. It is proposed that ii introduces an orthogonality between “being” (real component) and “becoming” (imaginary component).Temporal flow is interpreted as the continuous projection of undetermined future phases into determined past fixation.The increase of entropy and the arrow of time naturally arise as the cumulative effect of these projections—the gradual loss of imaginary-phase freedom. Within this complex-time geometry, quantum measurement is redefined as past fixation, the act that converts potential states within the imaginary domain into realized events on the real axis.A superposed quantum state therefore does not lack existence; rather, it exists within the imaginary-phase continuum as an undetermined future.Observation performs the transition Im(ψ)→Re(ψ)Im(ψ)→Re(ψ), turning potentiality into actuality. Quantum entanglement is reinterpreted as a temporally coherent relation already realified at its creation.Because the correlation itself is fixed in the real domain, no information transfer or superluminal signaling is required—the apparent simultaneity is the result of a shared past fixation.Once realified, the relation loses its imaginary component (dτ=0dτ=0), existing as a null-temporal entity outside ordinary spacetime.Consequently, the problem of nonlocality dissolves as a misunderstanding of temporal structure rather than spatial distance. At the macroscopic level, matter experiences time as the aggregate rhythm of countless microscopic realificationsamong interacting particles.Each crossing of eiθeiθ through the real axis imprints a discrete mark of actuality.The apparent continuity of classical time emerges as the statistical accumulation of these quantized projections—a self-recording process through which the universe continuously writes its own history. Ultimately, this study concludes that time is not an external parameter but the internal oscillation of existence itself—the ongoing conversion between potential and actual that underlies all physical and informational processes. Keywords:complex-time geometry; temporal projection; quantum measurement; entropy; arrow of time; quantum entanglement; nonlocality; ontology of time; self-recording process of reality
The analogy between quantum tunneling of particles and evanescent electromagnetic waves can be used to study particle tunneling. Possibilities for the measurement of the time delay resulting from the transmission of waves through an evanescent region, say with lower dielectric constant, are discussed. In contrast to particle tunneling, an electromagnetic pulse can consist of many photons and can be probed in a noninvasive way. We emphasize the delay of the centroid of an electromagnetic pulse transmitted below cutoff through a portion of a waveguide with the same cross section as the adjacent propagating guides. The boundary conditions at the interface between the propagating and the evanescent region lead to the same transmission and reflection coefficients as for a square-barrier tunneling problem. For a pulse restricted to a narrow frequency range, the time delay depends only on the frequency derivative of the phase shift associated with transmission. The delay of a centroid is just that; there is no deeper physical sense which links the incoming centroid to the outgoing centroid. For sufficiently long evanescent regions, the delay is independent of thickness.