Precision measurement beyond the shot-noise limit
The first applications of squeezed states to improve the precision of optical measurements beyond the limit set by the vacuum or zero-point fluctuations of the electromagnetic field have recently been reported. Improvements in the signal-to-noise ratio relative to the shot-noise limit for the detection of both amplitude and phase changes of the field have been achieved. Phase modulation in optical interferometers has been detected with an increase in sensitivity of 3dB relative to the shot-noise limit. Additionally, amplitude modulation was detected with an improvement in signal-to-noise of 2.5dB relative to the shot-noise limit. The experiments made use of squeezed light generated by an optical parametric oscillator to reduce the level of fluctuations below the level of vacuum fluctuations of the electromagnetic field.
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