Unbalanced Interferometers Beyond Coherence Length

ABSTRACT

Interferometry has been used widely in sensing applications. However, the technique is limited by the finite coherence time of the light sources when the interference paths are not balanced. As is well-known, quantum interference relies on measurement processes. The aforementioned requirement of path balance is for traditional intensity measurement from one detector. In this presentation, we consider two different methods: intensity correlation measurement between two detectors and homodyne measurement with a strong local oscillator. We find that they can be used to recover interference, which usually does not occur in intensity measurement by one detector. While the first method is based on two-photon coincidence measurement, the second one gives direct amplitude measurement and presents a new way of observing optical interference. We discuss various scenarios and data analysis methods to achieve interference of unbalanced delays in different paths with potential practical optical sensing applications and astronomical high-resolution imaging, and some startling implications for the fundamental Bohr’s complementarity principle for which-way interference and Dirac’s photon self-interference interpretation.

BIOGRAPHY

Professor Ou obtained his BS in 1984 from Peking University and Ph.D. in 1990 from the University of Rochester. He is now a Chair Professor at the City University of Hong Kong. Professor Ou is an expert in quantum optics, especially in quantum interference, for which he is the co-inventor of the well-known Hong-Ou-Mandel interferometer. He pioneered the field of multi-photon interference, which he summarized in the monograph “Quantum Multi-Photon Interference” published by Springer in 2007. Professor Ou’s current research focuses on quantum metrology, quantum sensing, quantum state engineering, quantum information and communication, and more fundamental quantum measurement and quantum coherence problems. Professor Ou is an Associate Editor of Optica Quantum, and is a fellow of the American Physical Society, of Optica (formerly Optical Society of America), and of the Physical Society of Hong Kong.