  Detector backaction can be completely evaded when the state of a one-electron
quantum cyclotron is detected, but it nonetheless significantly broadens the
quantum-jump resonance lineshapes from which the cyclotron frequency can be
deduced. This limits the accuracy with which the electron magnetic moment can
be determined to test the standard model's most precise prediction. A steady
state solution to a master equation, the first quantum calculation for the open
quantum cyclotron system, illustrates a method to circumvent the detection
backaction upon the measured frequency.
