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The Mind of El-rakhawi A Scholarly Reference Series in Advanced Physics and Quantum Theory DIRECT MEASUREMENT OF GRAVITATIONAL PHASE SHIFTS IN SINGLE-PHOTON OPEN-PATH TRAJECTORIES A New Experimental Paradigm for Quantum Gravity and Gravitational Quantum Optics

m el-rakhawi

Published Jul 24, 2026• 0 citations
Publisher

Abstract

The Mind of El-rakhawi A Scholarly Reference Series in Advanced Physics and Quantum Theory DIRECT MEASUREMENT OF GRAVITATIONAL PHASE SHIFTS IN SINGLE-PHOTON OPEN-PATH TRAJECTORIES A New Experimental Paradigm for Quantum Gravity and Gravitational Quantum Optics
DOI
10.5281/zenodo.21534884

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The gravitational phase accumulated by a quantum particle along an open path depends directly on the gravitational potential---which in general relativity is represented by the metric field---rather than solely on spacetime curvature. Although such open-path phases are gauge dependent and therefore usually regarded as unobservable, we show that this conclusion is incorrect. First, we argue that existing quantum optical experiments based on local homodyne tomography already reconstruct the open-path relative phase of spatially separated single-photon modes. Since the two photon paths experience different gravitational potentials, these measurements already contain an unnoticed gravitational open-path contribution. Second, we propose a modification of the large-scale fiber interferometer of Hilweg et al. that directly isolates and reads out the gravitational open-path phase without recombining the optical paths. The predicted signal is of the same order as the gravitational phase considered by Hilweg et al. but is obtained through quantum-state tomography rather than closed-loop interference. These results establish a direct operational method for measuring the gravitational potential through open-path quantum phases, providing strong evidence that the gravitational potential is a directly measurable physical quantity.
Over the past century, a large community within theoretical physics has been seeking a unified framework for quantum gravity. Yet, to date, there is still no experimental evidence of any non-classical features of gravity. While traditional experimental proposals would usually require immensely challenging Planck scale experiments, recent table-top protocols based on low-energy quantum control have opened a new avenue into the investigation of non-classical gravity. An approach that has sparked high interest, both in terms of experimental feasibility and of theoretical implications, is the indirect witnessing of non-classical gravity through the detection of its capacity to act as an entangling channel. Most discussions have been centred on the entanglement generation between two gravitationally coupled massive systems. In this work, we instead examine the entangling capacity of the gravitational interaction between two light pulses. We explain the main experimental and theoretical advantages of having a photonic protocol, and lay out the steps leading to the determination of the entangling phase, using the path integral formalism and linearised gravity. We establish a closed form formula for the entangling phase and provide an estimated order of magnitude of the average photon number required for the generation of appreciable phase. Using statistical analysis, we show how entanglement may be certified with lower phase signal.