Cue magnetic mines, but where are you getting the gravitic mines from?

I don't think it's realistically possible to do that totally undetected. Since the earth's magnetic field is so weak and field strength goes down rapidly as distance increases, malicious actors probably couldn't spoof patterns well enough to make the data look real, at least not without coming very close and staying near their target.

Just sell initially fake map

You don't need to hack the quantum sensor. You'll hack the regular computer around the sensor.