Scientists at institutions in Chicago, Germany and Belgium used a super-powerful X-ray beam at the Argonne National Laboratory to do it. It uses a half-century-old technique, diamond anvil cells, by adding a set of micro-anvils. A diamond anvil cell uses two brilliant-cut diamonds, like the kind you would see in an engagement ring, but instead of a point at the bottom, they have flat surfaces. A sample goes between the two diamonds, which are then compressed together to create high pressures. The technique can create about 320 to 360 gigapascals, which is about 3 million times the atmospheric pressure found on Earth's surface and about the pressure you would find at the core.