  A new type of quantum entangled interferometer was recently realized that
employs parametric amplifiers as the wave splitting and recombination elements.
The quantum entanglement stems from the parametric amplifiers, which produce
quantum correlated fields for probing the phase change signal in the
interferometer. This type of quantum entangled interferometer exhibits some
unique properties that are different from traditional beam splitter-based
interferometers such as Mach-Zehnder interferometers. Because of these
properties, it is superior to the traditional interferometers in many aspects,
especially in the phase measurement sensitivity. We will review its unique
properties and applications in quantum metrology and sensing, quantum
information, and quantum state engineering.
