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arXiv:2512.13722

Electron-positron pair creation induced by multi-pulse train of electric fields: effect of randomness in time-delay

Deepak Sah, Manoranjan P. Singh

quant-phhep-phhep-thSubmitted Dec 12, 2025• Announced Dec 16, 2025
arXivHTMLPDF

Abstract

We investigate the creation of electron-positron pairs (EPPs) in a sequence of alternating-sign, time-dependent electric field pulse trains by solving the quantum Vlasov equations. Specifically, we focus on Sauter-like pulse trains with random time delays between successive pulses, drawn from a Gaussian distribution wherein the extent of fluctuations is controlled by the standard deviation $σ_T$ of the distribution. We find that increasing $σ_T$ leads to a dramatic transformation in the longitudinal momentum spectrum. The well-known fringe pattern, akin to that in the multi-slit interference, gets significantly modified. The averaged spectra exhibit a robust Gaussian-like envelope with residual oscillations, which are much more prominent in the central momentum region. Notably, we find that in certain cases, stochastic time delays lead to a pronounced enhancement in the central peak of the distribution function for pulse train containing $N$ pulses. For example, for $N=20$ pulses, $σ_T \approx 31$ $[m^{-1}]$(about $17\%$ of the mean time delay) yields nearly a tenfold increase in the central peak, which for $σ_T \approx 50$ $[m^{-1}]$ (about $27\%$ of the mean time delay), scales up to $10^3.$ This may open up new possibilities for optimizing multi-pulse field configurations and guide future experimental designs aimed at maximizing EPPs creation.

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We investigate the creation of electron-positron pairs (EPPs) in a sequence of alternating-sign, time-dependent electric field pulse trains by solving the quantum Vlasov equations. Specifically, we focus on Sauter-like pulse trains with random time delays between successive pulses, drawn from a Gaussian distribution wherein the extent of fluctuations is controlled by the standard deviation σTσ_TσT​ of the distribution. We find that increasing σTσ_TσT​ leads to a dramatic transformation in the longitudinal momentum spectrum. The well-known fringe pattern, akin to that in the multi-slit interference, gets significantly modified. The averaged spectra exhibit a robust Gaussian-like envelope with residual oscillations, which are much more prominent in the central momentum region. Notably, we find that in certain cases, stochastic time delays lead to a pronounced enhancement in the central peak of the distribution function for pulse train containing NNN pulses. For example, for N=20N=20N=20 pulses, σT≈31σ_T \approx 31σT​≈31 [m−1][m^{-1}][m−1](about 17%17\%17% of the mean time delay) yields nearly a tenfold increase in the central peak, which for σT≈50σ_T \approx 50σT​≈50 [m−1][m^{-1}][m−1] (about 27%27\%27% of the mean time delay), scales up to 103.10^3.103. This may open up new possibilities for optimizing multi-pulse field configurations and guide future experimental designs aimed at maximizing EPPs creation.
Quantum entanglement, a defining feature of quantum theory, is generated dynamically by the Schwinger effect—the production of particle-antiparticle pairs from a strong electric field. In this work, we go beyond traditional particle-number analyses to study the quantum entanglement gen- erated in this process. We partition the system into momentum modes and calculate entanglement entropy and logarithmic negativity as functions of time. For a single Sauter pulse, entanglement exhibits a monotonic growth that closely tracks the pair creation process. Strikingly, a train of alternating pulses induces coherent interference, leading to a cumulative enhancement of entan- glement and revealing a clear interplay between successive creation events. Most significantly, we show that the temporal delay (𝑇) between pulses acts as a tunable parameter, controlling the level of entanglement via constructive or destructive interference. This tunability provides a distinct sig- nature of vacuum memory, establishing pair production as a platform for entanglement-controlled strong-field physics.
We investigate entropy of electron-positron pair production in time-dependent Sauter pulse electric field. Both cases of pair longitudinal momentum only and full momentum consideration are examined. We further examine three types of entropy, one is the usual entanglement entropy SES_{\text{E}}SE​, the other two extensions are thermal distribution entropy SThS_{\text{Th}}STh​, and that with the chemical potential correction, STh,CPS_{\text{Th,CP}}STh,CP​. For short pulse, SES_{\text{E}}SE​ is higher than SThS_{\text{Th}}STh​ and vice versa for long pulse. The chemical potential causes the single-particle average thermal distribution entropy STh,CPN\frac{S_{\text{Th,CP}}}{N}NSTh,CP​​ to exhibit non-monotonic behavior, similar to the single-particle average entanglement entropy SEN\frac{S_{\text{E}}}{N}NSE​​ in the short-pulse range. In the full momentum case, we calculate the thermal distribution entropy STh, US_{\text{Th, U}}STh, U​ via introducing the Unruh temperature as the local effective temperature. We find that both STh, US_{\text{Th, U}}STh, U​ and SES_{\text{E}}SE​ saturate asymptotically to the constant while the former has a larger asymptotic value. The results presented in this study reveals that the different entropies have some delicate relationships among them.
We investigate spin-resolved momentum distributions and phase vortices in multiphoton electron-positron pair production within a modified two-level model. This model retains the diagonal spinor inner-product terms neglected in the adiabatic approximation, thereby inducing spin-resolved transverse asymmetries in the momentum distribution. For a circularly polarized pulse, the handedness determines the winding direction of the quantized vortices, whereas for a linearly polarized pulse, the phase distribution exhibits nodal lines rather than quantized vortices. For two time-delayed circularly polarized pulses, the time delay introduces a relative phase that governs the multiphoton interference, which in turn drives the vortex evolution in each spin configuration. These results demonstrate that pulse polarization and time delay enable coherent control over vortex topology in pair production.
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We investigate the spin resolved vortex properties of electron positron pairs created from vacuum in time delayed, two color electromagnetic fields. By treating the temporal delay G as a continuous tuning parameter, we reveal a dynamic transition from interference-dominated domain patterns at G=0 to the nucleation of quantized vortex lattices at G=0.5. These topological structures exhibit a staggered arrangement analogous to von Karman vortex streets in fluid dynamics. We demonstrate that the momentum-space morphology is strictly governed by spin orbit selection rules, i.e., parallel spin configurations enforce a dipole-like connectivity, while anti-parallel configurations resolve into distinct quadrupole structures. This difference originates from the conservation of total angular momentum Jz, where the spin projection determines the required orbital angular momentum Lz of the created pairs. At large delays (G greater than 1), macroscopic vortex coherence dissolves into a chaotic phase landscope due to multi-channel interference, yet the spin-dependent nodal geometries remain robust. Our findings suggest that these topological signatures provide a high-fidelity diagnostic for the quantum dynamics of vacuum excitations in strong field QED.
Abstract Progress in reducing the duration of light pulses (down to one cycle of field oscillations or less), achieved in the last decades, has made it possible to experimentally observe and study a number of atomic-scale phenomena that occur at ultrafast times. Their study and observation are unavailable with conventional sources of monochromatic laser radiation. When using few- or subcycle pulses, a number of well-known phenomena in optics, which are well studied when using long monochromatic radiation sources, either lose their meaning, or their underlying physical mechanisms require revision. For example, the direct interference of subcycle pulses with their direct overlap is not possible due to their short duration. This note addresses the interference phenomenon, when a pair of subcycle pulses act on a medium, while do not simultaneously overlap inside it. In this case, it is not the pulses themselves that interfere in the medium, but the probability amplitudes of the bound states of the medium. Therefore the result of their impact on the medium can be interpreted as the interference of the areas of pulses—electric pulse areas (integral of the electric field strength over time) and envelope areas (integral of the slowly varying envelope of the electric field strength over time).