Making measurements at a precision limited only by quantum uncertainty is crucial for applications such as the detection of gravitational waves (1) or the search for dark matter (2). In this quest, physicists can reduce uncertainty in measurements of one variable at the expense of another (3, 4). Ultimately, however, the precision is often limited by the classical noise of the measurement apparatus. In principle, a solution to this problem is to amplify the signal relative to the classical noise. Readers familiar with cassette tapes may recognize this strategy, which is much like turning up the volume of music in a car so that it can be heard above the engine noise, only to have the tape hiss obscure the finer features of the music. On page 1163 of this issue, Burd et al. (5) report extremely sensitive measurements of the position of an individual ion, achieved by both suppressing quantum noise and amplifying signal.
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