Photocurrent shot noise represents the fundamental quantum limit of amplitude, phase and timing measurements of optical signals. It is generally assumed that non-classical states of light must be employed to alter the standard, time-invariant shot noise detection limit. However, in the case of the detection of periodic signals, correlations in the shot noise spectrum can impact the quantum limit of detection. Here we show how these correlations can be exploited to improve shot noise-limited optical pulse timing measurements by several orders of magnitude. This has allowed us to realize a photodetected pulse train timing noise floor at an unprecedented 25 zeptoseconds/sqrt(Hz), which is ~5 dB below the level predicted by the accepted time-invariant shot noise behavior. This new understanding of the shot noise of time-varying signals can be exploited to greatly improve photonic systems, impacting a wide range of communication, navigation, and precision measurement applications.
Citation: Nature Photonics
Pub Type: Journals
Microwave Photonics, Phase Noise, Shot noise, Timing Jitter, Ultrafast Optics