Quark Spheres are small, spherical devices that can harness inter and extra-dimensional energy using quark matter. It is used to mimic the DNA of an individual to stabilize dimensional energy.
Quark spheres were first used by Team Flash to extract Barry Allen from the Speed Force prison without destabilizing it. This sphere contained Barry's DNA, which tricked the prison into thinking it still had Barry in it, keeping the prison stable and releasing Barry through a portal in the center of the city.
Quark spheres were used again to help separate Jax and Stein from the Firestorm Matrix without the matrix becoming unstable. These spheres contained Jax's and Stein's DNA to trick the matrix into thinking they were still connected when Stein took the serum to shut down his and Jax's powers so they could be separate without it being a threat to both their lives. This ultimately killed Stein due to wounds he sustained on Earth-X and Jax being the only thing keeping him alive due to their connection.