Quantum dating was an extremely precise method of measuring a particle's age. Quantum dating could provide information not only on how old an object was, but from what time period that object was from, past or future.
In 2153, Jonathan Archer, acting on a tip from the Suliban Cabal's mysterious benefactor, quantum dated a component from the Xindi probe that attacked Earth. Archer showed the results, which read -420, to Admiral Forrest and Ambassador Soval, both of whom expressed surprise at the results, as quantum dating usually only registered in positive numbers. Using these results, Archer was able to prove that the component was from 420 years in the future.
Later that year, T'Pol ran quantum scans of the first Delphic Expanse sphere that the Enterprise NX-01 came across, to determine that it was at least a thousand years old. (ENT: "Anomaly")
In 2154, Degra quantum dated a Xindi initiation medal supplied to him by Captain Archer, who himself had received it from temporal agent Daniels, and determined that the medal itself was also from the future. (ENT: "Azati Prime")
Later that year, T'Pau proposed that quantum dating could prove that the Kir'Shara is from the time of Surak, after she and Archer brought the Kir'Shara to the Vulcan High Command. (ENT: "Kir'Shara")