By probing the electron-positron pair creation zone with incoming electrons that have controlled velocities, we can address the fundamental question of where the electrons are being created from the vacuum. It has been shown that the yield of the created positrons at targeted energies can be controlled via a second (subcritical) electric field that is placed far outside the creation zone. This is a clear indication of the nonlocal character of the pair-creation process.  We also demonstrate that the momentum distribution of particles created via the Schwinger process can be modulated by the local geometric phase of the quantum vacuum state. This modulation can be achieved by varying the electromagnetic scalar or vector potentials, without altering the strong fields themselves within the interaction region. The effect can be interpreted as a modification of the phase of virtual particles in the vacuum, drawing an analogy to the celebrated Aharonov-Bohm effect. These discovery not only advances our understanding of electromagnetic interactions in quantum field theory but also opens up new experimental opportunities for realizing Schwinger tunneling with existing laser facilities.

strong field QED, Schwinger process, quantum vacuum, nonlocality