Laboratory vacuum birefringence and Schwinger pair creation

4 problems

• Lowest laser intensity for observable dynamically assisted Schwinger pairs

  Open

  Pulling pairs out of empty space with a field alone needs a field about a thousand times stronger than the best lasers give, which is several million times their intensity. Adding a weak fast-oscillating field could lower the barrier, and the question is how much.

• Static magnetic field vacuum birefringence measured at the QED value

  Open

  A strong magnet should make the vacuum very slightly birefringent, by an amount far too small for any experiment so far. The question is whether any optical cavity experiment can reach the predicted value.

• Observation of tunneling pair creation in gamma-ray laser collisions

  Open

  A $\gamma$ ray colliding with a strong laser can turn into an electron-positron pair by quantum tunneling, the same process as Schwinger pair creation but in a moving frame. A 1997 experiment saw pair creation only in the weak-field regime, and the tunneling regime is still unobserved.

• First 5-sigma vacuum birefringence detection with an x-ray laser and optical laser

  Open

  An x-ray beam passing through the focus of a very intense laser should have a tiny fraction of its photons flip polarization because the vacuum acts like a crystal. The question is whether a planned experiment can see these few flipped photons above all background.