IT'S A QUANTUM UNIVERSE
Researchers publish new guide to measuring spacetime fluctuations
Signatures of Correlation of Spacetime Fluctuations in Laser Interferometers
image:
Cardiff's Gravity Exploration Institute team working on QUEST experiment. Credit: H Grote, Cardiff University.
view moreCredit: H Grote, Cardiff University
A team of researchers led by the University of Warwick has developed the first unified framework for detecting “spacetime fluctuations” - tiny, random distortions in the fabric of spacetime that appear in many attempts to unite quantum physics and gravity.
These subtle fluctuations, first envisaged by physicist John Wheeler, are thought to arise naturally in several leading theories of quantum gravity. But because different models of gravity predict different forms of these fluctuations, experimental teams have until now lacked clear guidance on what to look for.
The new study, published in Nature Communications addresses this challenge by sorting spacetime fluctuations into three broad categories, each defined by how organised the fluctuations are in space and time. For each category, the researchers mapped out the distinct, measurable signatures that would appear in laser interferometers - from the 4km long LIGO, to compact laboratory systems such as QUEST and GQuEST being developed in the UK (Cardiff University) and USA (Caltech) respectively.
Dr. Sharmila Balamurugan, Assistant Professor, University of Warwick and first author said: “Different models of gravity predict very different underlying trends in the random spacetime fluctuations, and that has left experimentalists without a clear target. Our work provides the first unified guide that translates these abstract, theoretical predictions into concrete, measurable signals.
“It means we can now test a whole class of quantum-gravity predictions using existing interferometers, rather than waiting for entirely new technologies. This is an important step towards bringing some of the most fundamental questions in physics firmly into the realm of experiment.”
The study found that:
- Tabletop interferometers beat LIGO in bandwidth
Despite being far smaller than LIGO, QUEST and GQuEST could provide more detailed information about the nature of spacetime fluctuations. Their wide frequency coverage allows them to detect all the characteristic signatures. - LIGO is an excellent “yes/no” detector.
Thanks to its long arm cavities, LIGO is highly sensitive to the mere presence of spacetime fluctuations — although the relevant frequencies lie above the range currently available in public data. - A long-running debate is resolved.
A debate about whether arm cavities help or hinder detection has been answered as here arm cavities do enhance an interferometer’s sensitivity to spacetime fluctuations, depending on the type of fluctuation being tested.
Dr. Sander Vermeulen, Caltech, co-author of the study said: “Interferometers can measure spacetime with extraordinary precision. However, to measure spacetime fluctuations with an interferometer, we need to know where - i.e. at what frequency - to look, and what the signal will look like. With our framework we can now predict this for a wide range of theories. Our results show that interferometers are powerful and versatile tools in the quest for quantum gravity.”
Crucially, the new framework developed here is agnostic of the underlying mechanism for the fluctuations: it requires only the mathematical description of the hypothesised fluctuations and the geometry of the instrument. This makes it a powerful tool not only for quantum-gravity tests but also for searches for stochastic gravitational waves, dark-matter signatures, and certain forms of instrumental noise.
Prof Animesh Datta, Professor of Theoretical Physics at Warwick concluded: “With this methodology, we can now treat any proposed model of spacetime fluctuations in a consistent, comparable way. In the coming years, we can use this to design smarter tabletop interferometers to confirm or refute possible theories of quantum or semiclassical gravity and even test new ideas about dark matter and stochastic gravitational waves.”
ENDS
Notes to Editors
Image Credits: H Grote, Cardiff University.
About the paper and funding:
The paper ‘Signatures of Correlation of Spacetime Fluctuations in Laser Interferometers’ has been published in Nature Communications. DOI: https://doi.org/10.1038/s41467-025-67313-3
This work was funded by the UK STFC “Quantum Technologies for Fundamental Physics” program (Grant Numbers ST/T006404/1, ST/W006308/1 and ST/Y004493/1) and the Leverhulme Trust under research grant ECF-2024-124 and RPG-2019-022.
About the University of Warwick
Founded in 1965, the University of Warwick is a world-leading institution known for its commitment to era-defining innovation across research and education. A connected ecosystem of staff, students and alumni, the University fosters transformative learning, interdisciplinary collaboration, and bold industry partnerships across state-of-the-art facilities in the UK and global satellite hubs. Here, spirited thinkers push boundaries, experiment, and challenge conventions to create a better world.
Journal
Nature Communications
Method of Research
Computational simulation/modeling
Article Title
Signatures of correlation of spacetime fluctuations in laser interferometers
Quantum measurements with entangled atomic clouds
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With three atomic clouds whose spins (blue) are entangled with each other at a distance, the researchers can measure the spatial variation of an electromagnetic field.
view moreCredit: Illustration: Enrique Sahagún, Scixel / University of Basel, Department of Physics
Researchers at the University of Basel and the Laboratoire Kastler Brossel have demonstrated how quantum mechanical entanglement can be used to measure several physical parameters simultaneously with greater precision.
Entanglement is probably the most puzzling phenomenon observed in quantum systems. It causes measurements on two quantum objects, even if they are at different locations, to exhibit statistical correlations that should not exist according to classical physics – it’s almost as if a measurement on one object influences the other one at a distance. The experimental demonstration of this effect, also known as the Einstein-Podolsky-Rosen paradox, was awarded the 2022 Nobel Prize in physics.
Now, a research team led by Prof. Dr. Philipp Treutlein at the University of Basel and Prof. Dr. Alice Sinatra at the Laboratoire Kastler Brossel (LKB) in Paris has shown that the entanglement of spatially separated quantum objects can also be used to measure several physical parameters simultaneously with increased precision. The researchers recently published their results in the scientific journal Science.
Improved measurements through entanglement
“Quantum metrology, which exploits quantum effects to improve measurements of physical quantities, is by now an established field of research,” says Treutlein. Fifteen years ago, he and his collaborators were among the first to perform experiments in which the spins of extremely cold atoms were entangled with each other. The entanglement allowed them to measure the direction of the atomic spins (which can be imagined as tiny compass needles) more precisely than would have been possible with independent spins without entanglement.
“However, those atoms were all in the same location,” Treutlein explains: “We have now extended this concept by distributing the atoms into up to three spatially separated clouds. As a result, the effects of entanglement act at a distance, just as in the EPR paradox.”
The idea behind this is that if one wants to measure, for instance, the spatial distribution of an electromagnetic field, one could use an entangled state of spatially separated atomic spins. Similarly to the measurement at a single location, the entanglement could then reduce the measurement uncertainties due to quantum mechanics and, to a large degree, also cancel other disturbances that act equally on all the atomic spins.
“So far, no one has performed such a quantum measurement with spatially separated entangled atomic clouds, and the theoretical framework for such measurements was also still unclear,” says Yifan Li, who was involved in the experiment as a postdoc in Treutlein’s group. Together with their colleagues at the LKB, Treutlein and his team investigated how the measurement uncertainty for the spatial distribution of an electromagnetic field could be minimized using such entangled clouds.
To achieve this, they first entangled the atomic spins into a single cloud and then split the cloud into three entangled parts. With only a few measurements, they were able to determine the field distribution with a distinctly better precision than would have been expected without the spatial entanglement.
Applications in atomic clocks and gravimeters
“Our measurement protocols can be directly applied to existing precision instruments such as optical lattice clocks,” says Lex Joosten, PhD student in the Basel group. In such clocks, atoms are trapped in an optical lattice created by laser beams and then used as extremely precise “clockworks”. The methods of the Basel researchers could be used to reduce specific measurement errors arising from the distribution of atoms across the lattice, thereby improving the precision of time measurements.
Another example of a practical application is atom interferometers, which can be used to measure the Earth’s gravitational acceleration. For some applications of these instruments, known as gravimeters, the main quantity of interest is the spatial variation of gravity, which can be measured with higher precision than before using the entanglement approach.
Journal
Science
Method of Research
Experimental study
Article Title
Multiparameter estimation with an array of entangled atomic sensors
Article Publication Date
22-Jan-2026
A new optical centrifuge is helping physicists probe the mysteries of superfluids
Centrifuge enables researchers to control the rotation of molecules suspended in liquid helium nano-droplets, bringing them a step closer to demystifying the behaviour of exotic, frictionless superfluids.
image:
Physicists at the University of British Columbia sent a laser beam of an optical centrifuge into helium nano-droplets doped with dimers of nitric oxide in order to control and study their rotation inside superfluid helium. (Valery Milner, University of British Columbia).
view moreCredit: Valery Milner, University of British Columbia
Physicists have used a new optical centrifuge to control the rotation of molecules suspended in liquid helium nano-droplets, bringing them a step closer to demystifying the behaviour of exotic, frictionless superfluids.
It’s the first demonstration of controlled spinning inside a superfluid—researchers can now directly set the direction and frequency of the molecule’s rotation, which is vital in studying how molecules interact with the quantum environment at various rotational frequencies. The method was outlined this week by researchers at the University of British Columbia (UBC) and colleagues at the University of Freiburg in the journal Physical Review Letters.
“Controlling the rotation of a molecule dissolved in any fluid is a challenge,” said Dr. Valery Milner, associate professor with UBC Physics and Astronomy and lead author on the paper.
“Dissolved molecules interact with the atomic or molecular constituents of the fluid, effectively getting bigger and harder to spin up. Imagine making a snowball: It’s very easy to move it when it’s small, but gets harder and harder as more snow gets attached to it.”
Superfluids like liquid helium are exotic states of matter, at near-absolute zero, that flow with no viscosity. But despite the lack of friction, they actually do act as solvents.
“The question of interest in the science of quantum matter, and the one this new approach will help us explore, is what changes from the perspective of the solvated—dissolved—molecule when you make the transition from a normal fluid to this type of quantum superfluid,” adds Dr. Milner.
A new spin on optical centrifuges
Conventional optical centrifuges have already been used to spin and study molecules in gases by shining a rotating laser pulse onto it. Molecules in the gas align with the beam’s electric field and rotate with the pulse. But the technique hasn’t worked yet with molecules suspended in a superfluid.
Dr. Milner and his team embedded the molecules in helium nano-droplets doped with dimers of nitric oxide, and introduced a short time delay between laser pulses. That caused interference that creates a much lower, constant rotation rate that increased the molecule’s “spinnability.”
With the new approach, the team will move on to scan the rotation frequency (using the new ‘control knob’ offered by the novel centrifuge) across a critical frequency, beyond which molecular rotation is expected to decay much faster due to the breakdown of superfluidity.
“It is not well understood how and when—for example at what frequency—this transition will happen at such a tiny atomic scale,” says Dr. Milner. “That’s the key area we’re investigating at the moment.”
The research was supported by the Natural Sciences and Engineering Research Council of Canada, the Canada Foundation for Innovation, and the BC Knowledge Development Fund.
Journal
Physical Review Letters
Method of Research
Experimental study
Article Publication Date
22-Jan-2026
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