A clock with 8×10−19 systematic uncertainty

We report an optical lattice clock with a total systematic uncertainty of 8.1×10−19 in fractional frequency units, representing the lowest uncertainty of any clock to date. The clock relies on interrogating the ultra-narrow 1S0→3P0 transition in a dilute ensemble of fermionic strontium atoms trapped in a vertically-oriented, shallow, one-dimensional optical lattice.