Sauter–Schwinger effect with a quantum gas

Abstract

The creation of particle-antiparticle pairs from vacuum by a large electric field is at the core of quantum electrodynamics. Despite the wide acceptance that this phenomenon occurs naturally when electric field strengths exceed E c ≈10 18 V m −1 , it has yet to be experimentally observed due to the limitations imposed by producing electric fields at this scale. The high degree of experimental control present in ultracold atomic systems allow experimentalists to create laboratory analogs to high-field phenomena. Here we emulated massive relativistic particles subject to large electric field strengths, thereby quantum-simulated particle-antiparticle pair creation, and experimentally explored particle creation from 'the Dirac vacuum'. Data collected from our analog system spans the full parameter regime from low applied field (negligible pair creation) below the Sauter-Schwinger limit, to high field (maximum rate of pair creation) far in excess of the Sauter-Schwinger limit. In our experiment, we perform direct measurements on an analog atomic system and show that this high-field phenomenon is well-characterized by Landau-Zener tunneling, well known in the atomic physics context, and we find full quantitative agreement with theory with no adjustable parameters.

Strong-field Breit-Wheeler pair production in $\mathrm{QED}_{2+1}$

“…Because of a complex technical implementation, these quantum simulators have been restricted so far to systems of lower dimensionality, so that the question arises, which differences occur as compared to 3+1 dimensions. In the realm of quantum electrodynamics, the progress in this field has led to an experimental implementation of the 1+1-dimensional Schwinger mechanism [50,51], which was investigated thoroughly by theoreticians [52][53][54], whereas current research efforts are spent towards QED 2+1 [55][56][57][58]. Hence, with the present study of the non-perturbative Breit-Wheeler pair creation we provide a scenario which may be further explored through the branch of quantum simulation.…”

The physics of adiabatic particle number in the Schwinger effect

“…This solution is ∩ p := −1/∪ p . It diverges in the free-field limit and so will not count the asymptotic number of pairs correctly, but when the field is on we can still define a vacuum and basis of states from it, and an instantaneous number of excitations (of something) Ñp (t) follows as in (8) but with ∪ p replaced by ∩ p . The physical content of this basis is easily found: a direct calculation shows that Ñp (t) is, due to Pauli blocking, the 'unoccupied' number density Ñp (t) = 1 − N p (t), i.e.…”

“…It is an example of quantum tunnelling (from the Dirac sea). The Schwinger effect can be the dominant mechanism behind charge loss from black holes [3], exhibits features of universality [4,5], and there are analogous effects in solidstate physics, often realised through Landau-Zener "interband" tunneling [6][7][8][9]. Experimental progress is bringing us closer to the point at which Schwinger pair production may be measurable in laser experiments [10][11][12][13][14], or through analogue processes [15].…”

“…There is therefore a 'pair producing part' of the exact solution to which adiabatic approximations are blind; a trans-series analysis of this result would be interesting to pursue. Our focus here though is on finding the meaning of the adiabatic particle number (8).…”

“…FIG. 1.Adiabatic pair number(8) calculated by numerically solving the Schrödinger equation in the Sauter pulse E(t) = E0 sech 2 ωt, a(t) = eE0/ω(1+tanh ωt), with E0 = 1/4, ω = 1/10 and p = 5/2, corresponding to final physical momentum = −5/2, in units where m = 1. The adiabatic number contains a great deal of structure, including a peak near t = 0 which is almost three orders of magnitude larger than the final number of pairs at t → ∞.…”