Classical Gravity Distorts Quantum Snapshots express
Photographing hummingbird wings with an ordinary camera gives a blurry smudge. For a sharp picture, you take many rapid shots from different angles and piece them together: that's how a quantum 'snapshot' is made. In the lab, scientists 'feel' the vibrations of a tiny mirror with a laser beam. By tracking changes in the light, they reconstruct the quantum state of this motion.
But gravity might behave differently. The Schrödinger–Newton theory suggests it remains a classical field. Then the mirror's own gravity makes it jiggle in sync with the measurement, like a camera shaking in unison with the subject. The resulting 'photograph' violates a fundamental ban, the Heisenberg uncertainty limit, like an impossibly ultra-sharp frame. Such anomalies would be a signal: if they appear, gravity is classical. It's a way to test the nature of gravity in the lab; if it turns out to be quantum, gravitational waves would appear as a stream of particles.
Original abstract
as written by the authors arXiv:2607.06967
Macroscopic optomechanical systems offer a promising testbed for distinguishing whether gravity acts as a quantum interaction or as a classical field. Schrodinger-Newton (SN) theory is the nonrelativistic limit of semi-classical gravity where quantum matter couples to classical gravity. Based on SN theory, this work investigates how classical self-gravity affects continuous quantum state tomography of a macroscopic mechanical oscillator monitored by variable-angle homodyne detection. In the Schrodinger-Newton (SN) theory, the measurement record arises from a different conditional test mass dynamics from that in quantum-gravity (QG)/standard quantum mechanics, consequently, applying the QG-optimised reconstruction map introduces an additional state-dependent contribution. We show that this contribution makes the reconstructed covariance depend on the chosen set of tomography angles and can drive the SN covariance--after QG filtering--outside the standard Gaussian-covariance domain set by the Heisenberg uncertainty principle. We quantify the resulting QG-SN distinguishability via the Hellinger distance and analyse its dependence on measurement strength and temperature. We then formulate the same issue in the broader setting of nonlinear quantum mechanics: when the system's conditional dynamics during the readout process depends on the state being inferred, the tomographic map acquires nonlinear, model-dependent corrections to the usual Radon or Gaussian reconstruction map.
According to the Schrödinger-Newton theory, every object gravitationally attracts itself, and this tiny force can distort a quantum experiment.