Fundamental Study of Unbalanced Quantum Interferometers Beyond Coherence Length

Description

The first quantum revolution enabled inventions such as solid-state transistors and lasers that have transformed nearly all aspects of our lives. The second quantum revolution, which promises disruptive technology that may change our daily life as well, involves designing and manipulating complex quantum systems that utilize quantum physics to bring quantum advantages in information processing, communication and sensing. The basic principle of quantum technology is quantum interference, which in optical regime is the phenomenon produced when two beams of light are brought together for wave superposition and shown in the form of beautiful fringes. Quantum interferometers are the fundamental building blocks in many protocols of quantum technology. Traditional interferometers are based on intensity measurement with one detector and require the balance of the paths of the two interfering beams to within the coherence length of the beams in order to have overlap in both space and time for wave superposition. This severely limits the application of traditional interferometry. Recent research revealed a new technique of intensity correlation between two detectors that can observe interference effect of some specific fields without the requirement of path-balancing, potentially extending the range of application of interferometry. Our recent theoretical analysis went one step further to cover more general types of fields including both continuous and pulsed waves. We also recently discovered that another measurement technique, namely, homodyne detection can reveal interference even between non-overlapping beams. This is a new paradigm in interferometry and will extend further the scope for applications in quantum technology in general. In this research program, we will apply the aforementioned two non-traditional detection methods, namely, intensity correlation and homodyne detection, to the observation of interference with the goal of revealing interference which is otherwise not present by traditional detection method due to path imbalance. We will apply the general idea of path-unbalanced interferometry to some specific systems and develop experimental platform to study this new approach in interferometry. More specifically, by using the two non-traditional measurement methods of intensity correlation and homodyne detection, we will investigate theoretically and experimentally various unbalanced interference schemes in different configurations. We will use different types of light sources such as classical thermal and coherent laser sources as well as quantum sources of entangled photons. As the potential applications, we explore the possibility of using the technique in remote sensing and synthetic aperture imaging in astronomical observation and demonstrate quantum advantages in enhanced sensitivity.