Researchers at the University of Illinois Urbana-Champaign, Stockholm University, Harvard University, and the Stevens Institute of Technology demonstrated how a network of quantum computers employing optical atomic clocks could probe the interplay between general relativity and quantum mechanics. The study, published in PRX Quantum, details an experiment utilizing three quantum computers separated by at least one kilometer in elevation to observe gravitational effects on shared quantum states, specifically W-states created via quantum teleportation. The authors predict that gravitational time dilation would manifest as specific interference patterns in these W-states, potentially revealing violations of the Born rule—a principle central to quantum theory—and providing direct evidence that standard quantum theory requires modification to account for general relativity. The feasibility of this protocol relies on existing distributed quantum computing technology and is being explored within the Q-NEXT Department of Energy quantum center network connecting the University of Chicago and Argonne National Laboratory.
Gravitational Effects on Quantum Systems
The study demonstrates that separating three quantum computers by as little as one kilometer in elevation is sufficient for the nonlinearity of Earth’s gravitational field to impact quantum states shared between them. This experimental setup is designed to provide direct evidence that standard quantum theory may require modification to account for general relativity, a long-standing question in theoretical physics. The researchers propose that observing alterations to the Born rule, a principle central to quantum theory, could reveal these modifications, as the rule predicts how multiple quantum sources combine and interfere.
The experiment utilizes so-called W-states – three-part quantum systems – which are integral to numerous protocols in quantum computing and communication. These W-states can be created on physically separated computers through the application of quantum teleportation, a key technology for distributed quantum computing. The researchers demonstrated that gravitational time dilation would cause specific interference patterns in the components of these W-states, offering a clear signature of potential Born rule violations within the experimental data.
The proposed protocol is feasible to implement using distributed quantum computing technology, leveraging connections between quantum nodes via special quantum networks. Illinois is participating in the construction of such a network organized by the Q-NEXT Department of Energy quantum center, connecting the University of Chicago and Argonne National Laboratory. Elevation differences of nearly one kilometer could potentially be achieved by utilizing a combination of underground laboratories at Fermilab and the tall buildings located in the Chicago metro area, facilitating the necessary conditions for these quantum gravity experiments.
Theoretical Basis for the Experiment
Past theoretical work suggests that curvature in space and time alters the Born rule, a tenet of quantum theory based on the linearity of quantum theory that translates abstract mathematics into experimental predictions. Observing alterations to this rule is challenging, as they would only appear in quantum systems exhibiting a certain level of intrinsic nonlinearity. The Born rule predicts how multiple quantum sources combine and interfere; in a collection of three quantum sources, the rule states that only pairwise interference is needed to describe the full system.
If gravity altered the Born rule, there would be a term allowing all three sources to interfere simultaneously. Testing this scenario necessitates a system with three sources spanning a sufficiently large nonlinearity to provide a discernable observable, requiring the most precise sensors currently available – optical atomic clocks – and elevation separations of kilometers. This led to the design of a three-node quantum network of optical atomic processor clocks for these quantum gravity experiments.
The study’s authors designed an experiment to test this prediction using W-states – three-part quantum systems integral to many protocols in quantum computing and communication. Current quantum technology allows for the creation of W-states on physically separated computers using quantum teleportation. The researchers demonstrated that gravitational time dilation would cause W-state components to display specific interference patterns, clarifying how Born rule violations would appear in experimental data.
Experimental Design and Feasibility
According to the study’s authors, the experiment is designed to explore one aspect of how quantum theory needs to be modified to account for general relativity. The strength of their procedure lies in its reliance on quantum information protocols that have been, or will soon be, demonstrated, making it relatively straightforward to implement in principle.
The Earth’s gravity, manifested as curvature in space and time, is expected to alter the rules of standard quantum theory. An experiment consisting of three quantum computers at different elevations can reveal the interplay between gravity and quantum mechanics, utilizing gravitational time dilation, where clocks at different locations in a gravitational field tick at different rates. The researchers used incredibly high precision quantum metrology with optical atomic clocks to explore time dilation near Earth, but no experiment has yet directly observed the effect of spacetime curvature on quantum mechanics itself.
The study designed an experiment to test the prediction that gravity alters the Born rule using W-states – three-part quantum systems integral to many protocols in quantum computing and communication. Current quantum technology has the means to create W-states on physically separated computers using quantum teleportation. The researchers demonstrated that gravitational time dilation would cause W-state components to display specific interference patterns, clarifying how Born rule violations would appear in experimental data.
The protocol is feasible to implement using distributed quantum computing technology, in which quantum nodes are connected by special quantum networks. Illinois is participating in the construction of such a network organized by the Q-NEXT Department of Energy quantum center, connecting the University of Chicago and Argonne National Laboratory, with potential future additions of Fermilab and other locations in the Chicago metro area. This infrastructure could achieve elevation differences of nearly one kilometer, utilizing a combination of underground labs at Fermilab and the tall buildings of Chicago.
Network Infrastructure and Future Prospects
The study’s authors designed an experiment to test this prediction using W-states – three-part quantum systems integral to many protocols in quantum computing and communication, demonstrating that gravitational time dilation would cause W-state components to display specific interference patterns, clarifying how Born rule violations would appear in experimental data. According to the study’s authors, the new protocol is feasible to implement using distributed quantum computing technology, in which quantum nodes are connected by special quantum networks. Illinois is participating in the construction of such a network organized by the Q-NEXT Department of Energy quantum center, connecting the University of Chicago and Argonne National Laboratory, with potential future additions of Fermilab and other locations in the Chicago metro area.
The researchers demonstrated that elevation differences of nearly one kilometer could be achieved using a combination of underground labs at Fermilab and the tall buildings of Chicago, facilitating these quantum gravity experiments. Igor Pikovski (Stockholm University and the Stevens Institute of Technology) and Johannes Borregaard (Harvard University) also contributed to this work, with the study, Probing curved spacetime with a distributed atomic processor clock, available online (DOI: 10.1103/q188-b1cr). Jacob Covey is an assistant professor of physics at the University of Illinois Urbana-Champaign, affiliated with the Illinois Quantum Information Science and Technology Center in the Materials Research Laboratory.
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