Emergent space-time meets emergent quantum phenomena: observing quantum phase transitions in a moving sample

Abstract: In material science, it was established that as the number of particles $ N $ in a material gets more and more, especially in the thermodynamic limit, various macroscopic quantum phenomena such as superconductivity, superfluidity, quantum magnetism, Fractional quantum Hall effects and various quantum or topological phase transitions (QPT) emerge in such non-relativistic quantum many-body systems. There is always a reservoir which exchanges energy and particles with the material. This is the essence of P. W. Anderson's great insight More is different ''. However, there is still a fundamental component missing in this general picture: How the More is different '' becomes different in a moving inertial frame or a moving sample? Here we address this outstanding problem.We demonstrate our claims by studying one of the simplest QPTs: Superfluid (SF)-Mott transitions of interacting bosons in a square lattice in a sample moving with a constant velocity $ \vec{v} $. We first elaborate the crucial difference between a moving sample and a moving inertial frame, stressing the crucial roles played by a reservoir in a grand canonical ensemble which is needed to study the SF-Mott transition in the first place. In this work, we mainly present the moving sample case and only discuss very briefly the moving inertial frame case. It is the moving which mixes the space and time. We also stress the important roles played by the underlying lattice. Doing various light or neutron scattering measurements in a moving sample may become an effective way not only measure various intrinsic properties of the materials, tune various quantum and topological phases through phase transitions, but also probe the new emergent space-time structure near any QPT.