Patent ID: 7426444

Claim:
A method for determining a phase shift acquired by an entangled N-qubit system represented by a NOON state, the method comprising: for M trials, producing an entangled probe-qubit system by coupling a probe electromagnetic field with each qubit system in the entangled N-qubit system, transferring a phase shift from the qubit systems to the probe electromagnetic field by transforming each qubit system state in the entangled probe-qubit system into a linear superposition of qubit basis states, performing a measurement on the probe electromagnetic field in order to obtain an associated measurement result, and based on the measurement result falling within a measurement-result interval of a larger continuous spectrum of measurement results, incrementing a counter associated with the measurement-result interval; producing a frequency distribution by normalizing a set of counters, each counter associated with each measurement result interval; and determining the phase shift by fitting a probability distribution associated with the probe electromagnetic field to the frequency distribution as a function of the phase shift.