  Superconducting devices, based on the Cooper pairing of electrons, are of
outstanding importance in existing and emergent technologies, ranging from
radiation detectors to quantum computers. Their performance is limited by
spurious broken Cooper pairs also known as quasiparticle excitations. In
state-of-the-art devices, the time-averaged number of quasiparticles can be on
the order of one. However, realizing a superconductor with no excitations
remains an outstanding challenge. Here, we experimentally demonstrate a
superconductor completely free of quasiparticles up to seconds. The
quasiparticle number on a mesoscopic superconductor is monitored in real time
by measuring the charge tunneling to a normal metal contact. Quiet
excitation-free periods are interrupted by random-in-time events, where one or
several Cooper pairs break, followed by a burst of charge tunneling within a
millisecond. Our results vindicate the opportunity to operate devices without
quasiparticles with potentially improved performance. In addition, our present
experiment probes the origins of nonequilibrium quasiparticles in it; the decay
of the Cooper pair breaking rate over several weeks following the initial
cooldown rules out processes arising from cosmic or long-lived radioactive
sources.
