  We present a scheme for high sensitivity charge detection in the integer
quantum Hall regime using two point contacts in a series. The setup is an
electronic analog of an optical Fabry-Perot interferometer. We show that for
small transmission through the point contacts the sensitivity of the
interferometer is very high due to multiple reflections at the point contacts.
The sensitivity can be further enhanced twice by using electrons in spin
entangled state. We show that for point contacts having different reflection
probabilities, the interferometer can be tuned for the quantum limited
measurement.
