To build a quantum sensor, light must be prepared in a carefully controlled state where its frequency, polarisation and intensity are all well controlled. Here, the polarisation of blue light is altered before it is used to cool the atoms to absolute zero.
Researchers from the Department of Physics have contributed to a major advance towards building large-scale quantum sensors capable of operating under real-world conditions. Ultimately, the work could help physicists probe the fundamental nature of dark matter, dark energy and gravitational waves. The results have been published in Nature.
Around 95% of the Universe is thought to be made up of dark matter and dark energy, but their nature remains one of the biggest unsolved questions in physics. One way to search for clues is to use quantum sensing to detect the tiny effects these phenomena may have on atoms. However, this requires researchers to measure extremely small signals that can easily be overwhelmed by background noise.
Long-baseline atom interferometers are emerging as one of the most promising technologies for this challenge. They use lasers to split clouds of atoms and then bring them back together, allowing minute changes in their motion to be measured with exceptional precision. These changes could be caused, for example, by a gravitational wave passing through the detector, or by a dark matter field shifting the energy levels of the atoms.
A major obstacle, however, is that the lasers used to control these experiments produce phase noise far larger than the signals researchers are trying to detect. If left uncorrected, this noise completely obscures the effects being measured.
To overcome this, scientists have proposed using a differential approach, in which two interferometers are compared so that shared noise cancels out. This method underpins plans for next-generation detectors, but until now it had not been demonstrated under realistic operating conditions.
The new study, from the Atom Interferometer Observatory and Network (AION) collaboration, has now shown that this approach is technically feasible in the regime where future detectors are expected to operate. Led by Imperial College London, AION brings together researchers from institutions across the UK to develop next-generation quantum sensing technologies.
Testing quantum sensors under realistic conditions
In the Imperial Ultracold Strontium Laboratory, the team built a tabletop prototype using two macroscopically separated clouds of ultracold strontium-87 atoms, interrogated by a single ultrastable clock laser.
The setup was designed to mimic the conditions expected in much larger future experiments, where controlling noise becomes increasingly difficult. To push the method to its limits, the team deliberately introduced large amounts of additional phase noise into the system, far more than clock lasers naturally produce, to simulate the conditions expected in long-baseline detectors.
Individually, each interferometer became unusable, with its signal obscured by noise. The interference patterns that normally allow measurements to be made were effectively erased.
However, when the two interferometers were compared, a clear signal could still be recovered. Although each individual measurement appeared random, the correlation between them revealed the underlying behaviour of the system. The combined measurement operated at the fundamental limit set by quantum physics, demonstrating that laser noise cancellation works as required.
The researchers then went a step further, introducing an additional oscillating signal into the system, similar to what might be produced by a passing gravitational wave or a dark matter field. This signal could still be detected clearly, even under conditions where neither interferometer alone contained usable information.
The results provide the first experimental validation of a key principle underlying long-baseline atom interferometers, helping to resolve a central challenge in their design. Professor Daniela Bortoletto from the Department of Physics at the, University of Oxford, is a member of the AION collaboration: 'This work shows what can be achieved through long-term investment in quantum technologies and fundamental physics. Our result validates a key principle behind future quantum sensors, opening the way to studies of gravitational waves and searches for dark matter. Results such as this highlight the scientific opportunities and international leadership that can emerge from sustained support for ambitious, curiosity-driven research.'
Jack Sander, Project Engineer for AION, said: ‘Oxford has played a significant role in the success of the AION-10 project, providing both substantial engineering expertise and senior leadership. In particular, our engineers helped define and realise designs underpinning a long baseline atom interferometer, translating ambitious physics requirements into practical, deliverable solutions. These contributions have been instrumental in addressing some of the experiment’s most demanding technical challenges and in advancing AION towards its scientific goals.’
DPhil student and member of the AION collaboration Jesse Schelfhout from the Department of Physics at the University of Oxford adds: ‘It is marvellous to see the injected signals faithfully recovered despite the high levels of simulated laser phase noise. I find the physics underlying the experiment fascinating – that an atom in two places at once can be such a nifty sensor – and look forward to seeing what discoveries await when the technology is scaled up including by the MAGIS-100 instrument that is due to finish construction next year.’
Towards next-generation detectors
The AION programme aims to develop these technologies for large-scale experiments capable of probing new regions of the Universe. This includes a proposal for a long-baseline atom interferometer as part of the Atom Interferometry CERN Experiment (AICE), which could enable sensitive searches for ultralight dark matter and other dark sector signatures.
Professor Christopher Foot from the Department of Physics at the University of Oxford, is another member of the AION collaboration: ‘The laser lab in Oxford uses an ultrahigh vacuum system that was constructed collaboratively within the AION project; this is designed to be suitable for future generations of devices even taller that the 100m instruments currently envisaged. These findings build on years of progress on quantum technology within the AION programme in lasers and ultracold strontium physics, advances that made the experiment possible.’
The technology underlying these experiments has wider applications. Ultracold atom sources, ultrastable lasers and precision interferometry are core platforms that underpin next-generation atomic clocks for precise navigation systems that do not rely on GPS. Atom interferometry, in transportable instruments, is also a tool for mapping tiny changes in the Earth’s gravity field.
The study was dedicated to the memory of Professor Ian Shipsey of Oxford, former Head of the Department of Physics, whose vision and leadership played a key role in building the AION collaboration.
The AION collaboration, led by Imperial College London, includes researchers from King’s College London and the Universities of Birmingham, Cambridge, Liverpool, and Oxford, together with STFC Rutherford Appleton Laboratory. The programme was supported by the Quantum Technologies for Fundamental Physics (QTFP) programme, a joint STFC–EPSRC initiative.
A prototype differential atom interferometer for fundamental physics, CFA Baynham et al, Nature, 17 June 2026