  Lattice gauge theories (LGTs) are one of the most fundamental subjects in
many-body physics, and has recently attracted considerable research interests
in quantum simulations. Here we experimentally investigate the emergent
$\mathbb{Z}_2$ gauge invariance in a 1D superconducting circuit with 10
transmon qubits. By precisely adjusting staggered longitudinal and transverse
fields to each qubit, we construct an effective Hamiltonian containing an LGT
and gauge-broken terms. The corresponding matter sector can exhibit a
localization, and there also exists a 3-qubit operator, of which the
expectation value can retain nonzero for a long time in low-energy regimes. The
above localization can be regarded as the confinement of matter fields, and the
3-body operator is the $\mathbb{Z}_2$ gauge generator. These experimental
results demonstrate that, despite the absence of gauge structure in the
effective Hamiltonian, $\mathbb{Z}_2$ gauge invariance can still emerge in
low-energy regimes. Our work provides a method for both theoretically and
experimentally studying the rich physics in quantum many-body systems with
emergent gauge invariance.
