Abstract
Quantum electrodynamics expects the vacuum is transformed into a polarizable medium under an
intense electromagnetic fi eld. This vacuum polarization results in various macroscopic phenomena, such
as vacuum birefringence, vacuum diffraction, and so on. An x-ray free electron laser (XFEL) is a
powerful probe to detect these phenomena thanks to its short wavelength and high peak brilliance. We
are searching for vacuum birefringence and vacuum diffraction using an XFEL and PW class optical
lasers at SACLA. In this paper, we present an overview and the current status of our experiment.
