Quantum Noise in Phase Measurement

Andrew J. Stevenson, Malcolm B. Gray, Hans‐A. Bachor +1 more

Two schemes for interferometric optical phase measurement, with sensitivity limited only by quantum noise in the light, are analyzed. Direct detection is applicable to signals at modulation frequencies away from the technical noise of the light, so that quantum noise dominates the measurement. Alternatively signals otherwise obscured by classical optical noise may be recovered with a phase-modulation technique that shifts the signals to a quantum-noise-limited region of the photocurrent spectrum. The analysis is tested experimentally by using a polarimetric electric-field sensor. In the direct-detection scheme quantum-noise-limited performance produced a phase sensitivity of 0.25 µrad. The indirect scheme allowed subkilohertz signals to be extracted from classical noise 67 dB greater with sensitivity approaching the quantum noise limit.

Mark S. Hillery, Marlan O. Scully

Paul Busch, Teiko Heinonen, PEKKA J. LAHTI

Jie Tang, JiaWei Wang, Zhenyu Guo +3 more

Squeezing-enhanced optical phase estimation can significantly improve the measurement sensitivity and effectively enhance the signal-to-noise ratio. Investigating the influence of inevitable losses and noise in quantum channels on phase measurement is of paramount importance. Here, we analyze and experimentally demonstrate the evolution of squeezing enhancement in phase measurement, particularly under a non-Markovian decoherence model characterized by a correlated Gaussian noise in a bosonic environment. We show that in a noise-added channel, where the benefits of squeezing-enhanced phase measurement are seemingly lost, the performance can be restored through the strategic introduction of classical correlated noise. This is the first, to the best of our knowledge, experimental evidence, showing that environmental memory effects can substantially enhance phase measurement performance in a squeezing-enhanced optical interferometer under the correlated Gaussian noise, providing valuable insights for practical quantum sensing in noisy environments.

H. Z. Zhao, Zhou Lu, A. M. Bacon +2 more

We measure phase-dependent fluorescence spectra for an elementary system: long-lived coherently driven two-level atoms in an atomic beam. Phase-dependent fluorescence spectra measure quadrature noise in the atomic radiation field. These noise spectra are obtained using a homodyne detection scheme that suppresses excess noise by subtracting signals from two identically prepared atomic samples. Noise spectra are obtained for atomic radiation which is in phase $(0\ifmmode^\circ\else\textdegree\fi{})$ and out of phase $(90\ifmmode^\circ\else\textdegree\fi{})$ with a resonant driving field, as well as $\ifmmode\pm\else\textpm\fi{}45\ifmmode^\circ\else\textdegree\fi{}$ out of phase with an off-resonant driving field. The measured phase-dependent fluorescence spectra are much richer than ordinary fluorescence spectra, and exhibit many novel features. Particularly interesting are phase-dependent noise spectra for off-resonant excitation. These strikingly exhibit direct manifestations of time ordering, which appear as large differences between the measured $45\ifmmode^\circ\else\textdegree\fi{}$ and $\ensuremath{-}45\ifmmode^\circ\else\textdegree\fi{}$ quadrature noise spectra. The measured noise spectra are in excellent agreement in magnitude and shape with the results of a quantum treatment using no free parameters.

Z. Hradil