  Floquet engineering, i.e. driving the system with periodic Hamiltonians, not
only provides great flexibility in analog quantum simulation, but also supports
phase structures of great richness. It has been proposed that Floquet systems
can support a discrete time-translation symmetry (TTS) broken phase, dubbed the
discrete time crystal (DTC). This proposal, as well as the exotic phase, has
attracted tremendous interest among the community of quantum simulation. Here
we report the observation of the DTC in an one-dimensional superconducting
qubit chain. We experimentally realize long-time stroboscopic quantum dynamics
of a periodically driven spin system consisting of 8 transmon qubits, and
obtain a lifetime of the DTC order limited by the coherence time of the
underlying physical platform. We also explore the crossover between the
discrete TTS broken and unbroken phases via various physical signatures. Our
work extends the usage of superconducting circuit systems in quantum simulation
of many-body physics, and provides an experimental tool for investigating
non-equilibrium dynamics and phase structures.
