Precision optical displacement measurements using biphotons

Abstract

We propose and examine the use of biphoton pairs, such as those created in parametric down conversion or four-wave mixing, to enhance the precision and the resolution of measuring optical displacements by position-sensitive detection. We show that the precision of measuring a small optical beam displacement with this method can be significantly enhanced by the correlation between the two photons, given the same optical mode. The improvement is largest if the correlations between the photons are strong, and falls off as the biphoton correlation weakens. More surprisingly, we find that the smallest resolvable parameter of a simple split detector scales as the inverse of the number of biphotons for small biphoton number ("Heisenberg scaling"), because the Fisher information diverges as the parameter to be estimated decreases in value. One usually sees this scaling only for systems with many entangled degrees of freedom. We discuss the transition for the split-detection scheme to the standard quantum limit scaling for imperfect correlations as the biphoton number is increased. An analysis of an N -pixel detector is also given to investigate the benefit of using a higher resolution detector. The physical limit of these metrology schemes is determined by the uncertainty in the birth zone of the biphoton in the nonlinear crystal.

Robust interferometric sensing using two-photon interference

“…Otherwise, a camera must be used to obtain a reasonable amount of the transverse spatial distribution of the beam, in order to evaluate the displacement. In this case, the ultimate precision limit for the estimation of θ with a beam of ν independent photons is [17,18,20] ∆θ…”

“…Monitoring of the tilt angle of an object is a metrological scenario that is relevant in several fields of science and technology [8][9][10][11]. A typical optical approach to this task consists in tracking the spatial or phase displacements of a light beam reflected by the object [12][13][14][15][16][17][18][19][20]. Procedures based on monitoring a light beam that has reflected from the object, illustrated in Fig.…”

Recent advances in mechanical torque studies of small-scale magnetism

“…It is possible that different scaling behaviour will emerge for measurements with correlated photon pairs; see for example Ref [155]…”

Quantum-Enhanced Sensing from Hyper-Entanglement

“…Estimation of tilt angles of mirrors is important in several fields of science [22][23][24][25]. A common procedure consists in detecting the spatial or phase displacement of a laser beam reflected by the mirror [26][27][28][29][30][31][32]. Our method, on the other hand, is based solely on a binary polarization measurement at the output of an interferometer with a displaced input beam.…”