Rubidium atoms let physicists retrodict quantum spin beyond uncertainty

Using 5.17 x 10^(10) rubidium atoms, researchers from Shanxi University, Fudan University, and the Niels Bohr Institute have demonstrated the ability to retrodict quantum spin with precision exceeding the limits imposed by the Heisenberg uncertainty relation. The team monitored spin observables, achieving variances 1.01 dB below the established bound for over 1.4 hours. This work reveals that restrictions on predicting quantum measurements do not apply to retrodictive guessing of past measurements. This finding builds on the seminal work of Werner Heisenberg, who first articulated the uncertainty relation in 1927. Using 5.17× 1010 rubidium atoms, this achievement allows physicists to infer the state of a quantum system in the past with greater precision than previously thought possible. This oscillator’s position and momentum operators, xA and pA, were then monitored through weak, continuous measurements. By analyzing measurement records obtained both before and after a specific time, t, the researchers…