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  • Featured in Physics
  • Open Access

Probing Curved Spacetime with a Distributed Atomic Processor Clock

Jacob P. Covey1,*, Igor Pikovski2,3,†, and Johannes Borregaard4,‡

  • *Contact author: jcovey@illinois.edu
  • †Contact author: pikovski@stevens.edu
  • ‡Contact author: borregaard@fas.harvard.edu
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PRX Quantum 6, 030310 – Published 21 July, 2025

DOI: https://doi.org/10.1103/q188-b1cr

Abstract

Quantum dynamics on curved spacetime has never been directly probed beyond the Newtonian limit. Although we can describe such dynamics theoretically, experiments would provide empirical evidence that quantum theory holds even in this extreme limit. The practical challenge is the minute spacetime curvature difference over the length scale of the typical extent of quantum effects. Here, we propose a quantum network of alkaline earth (like) atomic processors for constructing a distributed quantum state that is sensitive to the differential proper time between its constituent atomic processor nodes, implementing a quantum observable that is affected by post-Newtonian curved spacetime. Conceptually, we propose to delocalize one clock between three locations by encoding the presence or absence of a clock into the state of the local atoms. By separating three atomic nodes over approximately kilometer-scale elevation differences and distributing one clock between them via a W state, we demonstrate that the curvature of spacetime is manifest in the interference of the three different proper times that give rise to three distinct beat notes in our nonlocal observable. We further demonstrate that N-atom entanglement within each node enhances the interrogation bandwidth by a factor of N. We discuss how our proposed system can probe new facets of fundamental physics, such as the linearity, unitarity, and probabilistic nature of quantum theory on curved spacetime. Our protocol combines several recent advances with neutral atom and trapped ions to realize a novel quantum probe of gravity uniquely enabled by quantum networks.

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Testing Quantum Theory in Curved Spacetime

Published 21 July, 2025

A proposed experiment could shed light on the unknown interplay of quantum theory and general relativity.

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Popular Summary

Quantum theory and general relativity are the two fundamental theories of modern physics—both tested and confirmed to great precision. But how do these two theories meet? Could one of them, or both, require modification where they intertwine? While a full theory of quantum gravity remains lacking, there are some suggestions that quantum principles might change in the presence of curved spacetime. Here, we show that modern quantum networking technologies can enable the first experiments to probe this interplay of the two theories and test quantum theory on curved spacetime.

Our protocol is based on two recent technologies—optical atomic clocks and quantum networks—that are being developed to distribute quantum entanglement over large distances. We show that one can delocalize a single optical atomic clock over three locations with kilometer-scale separations based on the use of quantum networking nodes composed of atom arrays. Each pair of nodes can share entangled Bell pairs on demand. The evolution of the clock is then delocalized over all three nodes, and it records different times because of the presence of the gravitational field. Subsequent quantum teleportation to a single node would allow us to observe a three-node interference between all three times, revealing how quantum interference, time dilation, and spacetime curvature all intertwine.

Our work combines techniques from quantum networking, quantum enhanced metrology, and distributed quantum computing to offer a first avenue to test quantum theory on curved spacetime. It may reveal whether our current theories survive or whether unexpected new physics can emerge.

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PRX Quantum 6, 030310– Published 21 July, 2025
  • Received 24 February 2025
  • Accepted 22 May 2025
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