Quantum Chromodynamics (QCD) predicts a transition from normal hadronic matter to a hot and/or dense phase where the quarks and gluons are no longer bound together and can move freely. Hot quark gluon plasmas with remarkable properties are produced in high energy collisions of heavy nuclei at the Relativistic Heavy Ion Collider (RHIC) in the U.S. and at the LHC in Europe.

Vanishingly small shear viscosity to entropy density ratio means that they flow essentially without internal friction. Such plasmas are found to be very opaque to particles which experience the strong interaction. I will discuss how we probe transport properties of quark gluon plasma using hadron jets arising from quarks or gluons transiting the plasma. Small colliding systems may also produce a small droplet of quark gluon plasma, implying that it can emerge from the cold, dense gluonic matter deep inside nuclei within 1 fm/c. I will show how a future electron-ion collider will help address this question.