Reaching the quantum limit of measurement: quantum SU(1,1) interferometry

Synopsis

Interferometry makes use of interference of light to realize precise measurements of the phase change induced by the physical quantities encoded in the optical path length. Examples of these physical quantities include displacement, change of refractive index, magnetic field and local gravity field. And hence interferometry is widely applied in the fields of astronomy, metrology and spectroscopy. The sensitivity and resolution of traditional interferometers that use linear optical elements and classical light has been shown to be limited by the standard limit, i.e., the uncertainty of measurement outcome is proportional to , where  is the average number of photons imported to the interferometer. However, quantum mechanics predicts that the quantum limit has the uncertainty proportional to : this is beyond the standard limit. One approach to reach the quantum limit of measurement is to replace linear optical elements in the traditional interferometer with nonlinear optical devices. Since the transformation to the light fields induced by the nonlinear devices can be characterized by the special unitary (1,1) (SU(1,1)) group, this technique is called SU(1,1) interferometry. Even though the theory of SU(1,1) interferometry has been developed for fifty years, this technology has not yet been realized until the recently modified scheme is proposed. In this talk, I will introduce SU(1,1) interferometry and its comparison to traditional interferometry. Moreover, the standard limit and quantum limit will be discussed.