According to a recent study result published in PRX Quantum, which was created in cooperation between Johannes Borregaard at Harvard University, Jacob Covey at the University of Illinois at Urbana-Champaign, and Igor Pikovski at Stevens Institute of Technology, quantum networks could be more adaptable than previously believed.
A quantum network of distant clocks. The entangled clocks can test how quantum theory behaves in the presence of curved space-time as predicted by Einstein, or whether our current theories break down. Image Credit: Igor Pikovski
Globally, quantum networking is developing quickly. The capacity to connect quantum computers worldwide and implement secure communication at scale is a crucial quantum technology that will make a global quantum internet possible. On Earth and in space, the race to fulfill this goal is already underway.
In the first test of its kind, researchers have demonstrated that this technology can investigate the effects of curved space-time on quantum theory.
Quantum physics has passed all of its tests thus far. However, how it functions when Einstein's theory of gravity, general relativity, is included is unclear. According to Einstein's theory, gravity is no longer a force, but rather the outcome of altering curved space-time.
This produces unique effects, such as the slowing of time around planets. The phenomenon has been observed and proven to a great degree of precision.
But how does the shifting passage of time influence quantum mechanics? Could quantum theory, general relativity, or both require modifications where they intertwine? While a comprehensive theory of quantum gravity is still absent, there are indications that quantum principles could change in the presence of curved spacetime. However, experimentally investigating this border has been impossible thus far.
Pikovski and Borregaard showed in a previous study titled Testing Quantum Theory on Curved Spacetime with Quantum Networks, which was published on May 27th, 2025, in Physical Review Research, that the time has come for experiments to investigate these topics using quantum networks.
They demonstrated how two independent but related aspects of quantum theory and gravity interact at the same time. In quantum theory, superpositions exist, and matter may exist in both particular definite states and mixes of them at the same time.
This fact is used in quantum computing to create qubits, which are superpositions of the numbers 0 and 1. Such qubits can then be dispersed across great distances via quantum networks. However, as time itself varies in the region of Earth, these qubits would likewise be impacted by curved space-time.
The researchers demonstrated that distinct time-flows in superposition would be picked up by superpositions of atomic clocks in quantum networks, which paves the way for further investigation into the interactions between curved space-time and quantum theory.
The interplay between quantum theory and gravity is one of the most challenging problems in physics today, but also fascinating. Quantum networks will help us test this interplay for the first time in actual experiments.
Igor Pikovski, Study Co-author and Geoffrey S. Inman Junior Professor, Stevens Institute of Technology
Pikovski and Borregaard then collaborated with Covey's lab to create a specific protocol. The group demonstrated how so-called entangled W-states may be used to spread quantum effects among network nodes and how interference between these entangled systems can be captured.
A test of quantum theory on curved space-time can be accomplished by taking advantage of contemporary quantum capabilities, such as entangled Bell-pairs (maximally entangled states of two qubits) in atom arrays and quantum teleportation (transferring the quantum state of a particle to another particle).
Pikovski added, “We assume that quantum theory holds everywhere but we really do not know if this is true. It might be that gravity changes how quantum mechanics works. In fact, some theories suggest such modifications, and quantum technology will be able to test that.”
The findings of Pikovski, Covey, and Borregaard show that quantum networks provide special possibilities for the study of basic physics that are not possible with conventional sensing, in addition to being a practical instrument for a future quantum internet. The behavior of quantum mechanics on curved space-time can now be tested, at least.
Journal Reference:
Covey, J. P. et al. (2025) Probing curved spacetime with a distributed atomic processor clock. PRX Quantum. doi.org/10.1103/q188-b1cr.