  Quantum metrology aims at achieving enhanced performance in measuring unknown
parameters by utilizing quantum resources. Thus, quantum metrology is an
important application of quantum technologies. Photonic systems can implement
these metrological tasks with simpler experimental techniques. We present a
scheme for improved parameter estimation by introducing entangled generalized
coherent states (EGCS) for photonic quantum metrology. These states show
enhanced sensitivity beyond the classical and Heisenberg limits and prove to be
advantageous as compared to the entangled coherent and NOON states. Further, we
also propose a scheme for experimentally generating certain entangled
generalized coherent states with current technology.
