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arXiv:2602.09125

Quantum State Characterization of Gravitational Waves via Graviton Counting Statistics

Kristian Toccacelo, Thomas Beitel, Ulrik Lund Andersen, Igor Pikovski

quant-phgr-qcSubmitted Feb 9, 2026• Announced Feb 11, 2026
arXivHTMLPDF

Abstract

Although gravitational waves are now routinely observed, the detection of individual gravitons has long been regarded as impossible. Recent work, however, has demonstrated that single-graviton detection can be achieved and may be feasible in the near future. Here we show that beyond mere particle detection, these detectors provide access to the quantum state and particle statistics of gravitational waves. We show that graviton detection probabilities enable the discrimination between squeezed, coherent, and thermal radiation. We further demonstrate that the full quantum statistics contained in the second-order correlation function of the passing wave can be directly measured at the detector, independent of the weak gravitational interaction strength. Building on recent quantum-optical techniques, this capability opens the way to full quantum state tomography of Gaussian states. Our results demonstrate that single-graviton detection is not only of foundational significance but also of practical value, allowing for the characterization of quantum statistics and the states of the gravitational radiation field, which remain currently unknown.

Comments
17 pages, 3 figures

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Although gravitational waves are now routinely observed, the detection of individual gravitons has long been regarded as impossible. Recent work, however, has demonstrated that single-graviton detection can be achieved and may be feasible in the near future. Here we show that beyond mere particle detection, these detectors provide access to the quantum state and particle statistics of gravitational waves. We show that graviton detection probabilities enable the discrimination between squeezed, coherent, and thermal radiation. We further demonstrate that the full quantum statistics contained in the second-order correlation function of the passing wave can be directly measured at the detector, independent of the weak gravitational interaction strength. Building on recent quantum-optical techniques, this capability opens the way to full quantum state tomography of Gaussian states. Our results demonstrate that single-graviton detection is not only of foundational significance but also of practical value, allowing for the characterization of quantum statistics and the states of the gravitational radiation field, which remain currently unknown.
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Among the revolutionary predictions of Einstein’s theory of general relativity is the existence of gravitational waves, which are perturbations in the fabric of spacetime that travel at the speed of light. The first indirect evidence pointing to their existence came from the observation of the Hulse-Taylor pulsar in 1974[4]. More recently, gravitational wave observatories like the Laser Interferometer Gravitational-wave Observatory (LIGO) and Virgo have been built with the purpose of detecting gravitational waves (GW) directly, providing not only further evidence in support of general relativity, but also a whole new way of viewing the cosmos. The strain produced by a passing gravitational wave (namely, the relative change in the length of the matter a gravitational wave passes through) is so small that the best sensitivity achieved by the detectors has not produced a positive detection as of today. With a clear understanding that there should be gravitational waves, scientists are working on improving the sensitivity of the detectors to increase the likelihood of a detection. One of the main sources of noise for the next generation gravitational wave detectors, such as advanced LIGO, is shot noise. Shot noise dominates the noise spectrum above a few hundred Hz. This noise is due to uncertainties in quantum statistics, according to the generalized uncertainty principle. There are two ways to reduce the shot noise. The first way is to increase the intensity of the