Vacuum pair production in spatially asymmetric time-oscillating electric fields

We investigate electron-positron pair production from the quantum vacuum in spatially asymmetric, oscillating electric fields using the Dirac-Heisenberg-Wigner formalism in <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:mn>1</a:mn><a:mo>+</a:mo><a:mn>1</a:mn></a:mrow></a:math> dimensions. The electric field is strongly space-time dependent [<c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi>E</c:mi><c:mo stretchy="false">(</c:mo><c:mi>x</c:mi><c:mo>,</c:mo><c:mi>t</c:mi><c:mo stretchy="false">)</c:mo><c:msub><c:mi mathvariant="bold">e</c:mi><c:mi>x</c:mi></c:msub></c:math>] and characterized by both spatial asymmetry and temporal oscillations. The temporal dynamics incorporate multiple modulation mechanisms, including variations in central frequency, frequency chirping, and phase modulation. Our results show that spatial asymmetry significantly enhances pair production compared to symmetric field configurations. Furthermore, optimal tuning of temporal parameters, such as the frequency <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"><h:mi>ω</h:mi></h:math> and chirp parameter <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"><j:mi>b</j:mi></j:math>, can further amplify the yield. For <l:math xmlns:l="http://www.w3.org/1998/Math/MathML" display="inline"><l:mi>ω</l:mi><l:mo>≳</l:mo><l:mn>0.4</l:mn><l:mi>m</l:mi></l:math>, the momentum spectra exhibit oscillatory structures dominated by multiphoton processes, whereas low-frequency fields (<n:math xmlns:n="http://www.w3.org/1998/Math/MathML" display="inline"><n:mi>ω</n:mi><n:mo>≲</n:mo><n:mn>0.3</n:mn><n:mi>m</n:mi></n:math>) result in tunneling-dominated Gaussian distributions. Chirped fields introduce spectral asymmetry and interference patterns, with peak yields increasing by up to a factor of 9 for <p:math xmlns:p="http://www.w3.org/1998/Math/MathML" display="inline"><p:mi>ω</p:mi><p:mo>=</p:mo><p:mn>0.7</p:mn><p:mi>m</p:mi></p:math> and <r:math xmlns:r="http://www.w3.org/1998/Math/MathML" display="inline"><r:mi>b</r:mi><r:mo>=</r:mo><r:mn>0.5</r:mn><r:mi>ω</r:mi><r:mo>/</r:mo><r:mi>τ</r:mi></r:math>. These findings offer a promising approach for optimizing vacuum pair production in experimentally realizable spatiotemporal field configurations.