  The GQuEST (Gravity from the Quantum Entanglement of Space-Time) experiment
uses tabletop-scale Michelson laser interferometers to probe for fluctuations
in space-time. We present an interferometer design featuring a novel photon
counting readout method that provides unprecedented sensitivity, as it is not
subject to the interferometric standard quantum limit. We evaluate the
potential of this design to measure space-time fluctuations motivated by recent
`geontropic' quantum gravity models. The accelerated accrual of statistical
power offered by the photon counting readout enables GQuEST to detect the
predicted quantum gravity phenomena within measurement times at least 100 times
shorter than equivalent conventional interferometers. The GQuEST design thus
enables a fast and sensitive search for signatures of quantum gravity in a
laboratory-scale experiment.
