Background suppression in quantum sensing of dark matter via collective entangled-state projection

We show that measuring dark matter signal by projecting quantum sensors in the collective excited state can highly suppress the noncollective noise background, hence improving the sensitivity significantly. We trace the evolution of the sensors’ state in the presence of both dark matter effect and sensors’ decoherence effects, optimizing the protocol execution time, and show that the suppression of background by a factor equal to the number of sensors is possible. This method does not require the entanglement of sensors during the signal accumulation time, hence circumventing the difficulty of maintaining the lifetime of the entangled state that is present in other enhancement proposals. This protocol is also general regarding the type of qubit sensors.