  In the fundamental laws of physics, gauge fields mediate the interaction
between charged particles. An example is quantum electrodynamics -- the theory
of electrons interacting with the electromagnetic field -- based on U(1) gauge
symmetry. Solving such gauge theories is in general a hard problem for
classical computational techniques. While quantum computers suggest a way
forward, it is difficult to build large-scale digital quantum devices required
for complex simulations. Here, we propose a fully scalable analog quantum
simulator of a U(1) gauge theory in one spatial dimension. To engineer the
local gauge symmetry, we employ inter-species spin-changing collisions in an
atomic mixture. We demonstrate the experimental realization of the elementary
building block as a key step towards a platform for large-scale quantum
simulations of continuous gauge theories.
