  The possibility that neutrinos may be their own antiparticles, unique among
the known fundamental particles, arises from the symmetric theory of fermions
proposed by Ettore Majorana in 1937. Given the profound consequences of such
Majorana neutrinos, among which is a potential explanation for the
matter-antimatter asymmetry of the universe via leptogenesis, the Majorana
nature of neutrinos commands intense experimental scrutiny globally; one of the
primary experimental probes is neutrinoless double beta ($0 \nu \beta \beta$)
decay. Here we show results from the search for $0 \nu \beta \beta$ decay of
$^{130}$Te, using the latest advanced cryogenic calorimeters with the CUORE
experiment. CUORE, operating just 10 millikelvin above absolute zero, has
pushed the state of the art on three frontiers: the sheer mass held at such
ultra-low temperatures, operational longevity, and the low levels of ionising
radiation emanating from the cryogenic infrastructure. We find no evidence for
$0 \nu \beta \beta$ decay and set a lower bound of $T_{1/2}^{0 \nu} > 2.2
\times 10^{25}$ years at a 90% credibility interval. We discuss potential
applications of the advances made with CUORE to other fields such as direct
dark matter, neutrino and nuclear physics searches and large-scale quantum
computing, which can benefit from sustained operation of large payloads in a
low-radioactivity, ultra-low temperature cryogenic environment.
