Edge-state Fabry-Perot interferometer as a high-sensitivity charge detector

We present a scheme for high-sensitivity and high-efficiency charge detection in the integer quantum-Hall regime using two point contacts in 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 detector can be tuned for the quantum-limited measurement.