title: Quantum coherence between two atoms beyond Q=10(15).
abstract: We place two atoms in quantum superposition states and observe coherent phase evolution for 3.4×10(15) cycles. Correlation signals from the two atoms yield information about their relative phase even after the probe radiation has decohered. This technique allowed a frequency comparison of two (27)Al(+) ions with fractional uncertainty 3.7(-0.8)(+1.0)×10(-16)/√[τ/s]. Two measures of the Q factor are reported: The Q factor derived from quantum coherence is 3.4(-1.1)(+2.4)×10(16), and the spectroscopic Q factor for a Ramsey time of 3 s is 6.7×10(15). We demonstrate a method to detect the individual quantum states of two Al(+) ions in a Mg(+)-Al(+)-Al(+) linear ion chain without spatially resolving the ions.
authors: Time and Frequency Division, National Institute of Standards and Technology, Boulder, Colorado 80305, USA. chinwen@nist.gov
authors: C W
authors: CW
authors: Chou
authors: D B
authors: DB
authors: Hume
authors: M J
authors: MJ
authors: Thorpe
authors: D J
authors: DJ
authors: Wineland
authors: T
authors: T
authors: Rosenband