Imagine two particles so interconnected that measuring one immediately reveals information about the other, even if the particles are light–years apart. This phenomenon, known as quantum entanglement, is the foundation of a variety of technologies such as quantum cryptography and quantum computing. However, entangled states are notoriously difficult to control. Now, for the first time, a team of physicists in Japan has performed a collective quantum measurement on a W state comprising three entangled photons. This allowed them to analyse the three entangled photons at once rather than one at a time. This achievement, reported in Science Advances, marks a significant step towards the practical development of quantum technologies.

Physicists usually measure entangled particles using a technique known as quantum tomography. In this method, many identical copies of a particle are prepared, and each copy is measured at a different angle. The results of these measurements are then combined to reconstruct its full quantum state. To visualize this, imagine being asked to take a family photo. Instead of taking one group picture, you have to photograph each family member individually and then combine all the photos into a single portrait. Now imagine taking a photo properly: taking one photograph of the entire family. This is essentially what happens in an entangled measurement: where all particles are measured simultaneously rather than separately. This approach allows for significantly faster and more efficient measurements.

So far, for three-particle systems, entangled measurements have only been performed on Greenberger–Horne–Zeilinger (GHZ) states, where all qubits (quantum bits of a system) are either in one state or another. Until now, no one had carried out an entangled measurement for a more complicated set of states known as W states, which do not share this all-or-nothing property. In their experiment, the researchers at Kyoto University and Hiroshima University specifically used the simplest type of W state, made up of three photons, where each photon’s polarization (horizontal or vertical) is represented by one qubit.

“In a GHZ state, if you measure one qubit, the whole superposition collapses. But in a W state, even if you measure one particle, entanglement still remains,” explains Shigeki Takeuchi, corresponding author of the paper describing the study. This robustness makes the W state particularly appealing for quantum technologies.

Fourier transformations

The team took advantage of the fact that different W states look almost identical but differ by tiny phase shift, which acts as a hidden label that distinguishes one state from another. Using a tool called a discrete Fourier transform (DFT) circuit, researchers were able to “decode” this phase and tell the states apart.

The DFT exploits a special type of symmetry inherent to W states. Since the method relies on symmetry, in principle it can be extended to systems containing any number of photons. The researchers prepared photons in controlled polarization states and ran them through the DFT, which provided each state’s phase label. After, the photons were sent through polarizing beam splitters that separate them into vertically and horizontally polarized groups. By counting both sets of photons, and combining this with information from the DFT, the team could identify the W state.

The experiment identified the correct W state about 87% of the time, well above the 15% success rate typically achieved using tomography-based measurements. Maintaining this level of performance was a challenge, as tiny fluctuations in optical paths or photon loss can easily destroy the fragile interference pattern. The fact that the team could maintain stable performance long enough to collect statistically reliable data marks an important technical milestone.

Scalable to larger systems

“Our device is not just a single-shot measurement: it works with 100% efficiency,” Takeuchi adds. “Most linear optical protocols are probabilistic, but here the success probability is unity.” Although demonstrated with three photons, this procedure is directly scalable to larger systems, as the key insight is the symmetry that the DFT can detect.

“In terms of applications, quantum communication seems the most promising,” says Takeuchi. “Because our device is highly efficient, our protocol could be used for robust communication between quantum computer chips. The next step is to build all of this on a tiny photonic chip, which would reduce errors and photon loss and help make this technology practical for real quantum computers and communication networks.”

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Physicists at the University of Tokyo, Japan have performed quantum mechanical squeezing on a nanoparticle for the first time. The feat, which they achieved by levitating the particle and rapidly varying the frequency at which it oscillates, could allow us to better understand how very small particles transition between classical and quantum behaviours. It could also lead to improvements in quantum sensors.

Oscillating objects that are smaller than a few microns in diameter have applications in many areas of quantum technology. These include optical clocks and superconducting devices as well as quantum sensors. Such objects are small enough to be affected by Heisenberg’s uncertainty principle, which places a limit on how precisely we can simultaneously measure the position and momentum of a quantum object. More specifically, the product of the measurement uncertainties in the position and momentum of such an object must be greater than or equal to ħ/2, where ħ is the reduced Planck constant.

In these circumstances, the only way to decrease the uncertainty in one variable – for example, the position – is to boost the uncertainty in the other. This process has no classical equivalent and is called squeezing because reducing uncertainty along one axis of position-momentum space creates a “bulge” in the other, like squeezing a balloon.

A charge-neutral nanoparticle levitated in an optical lattice

In the new work, which is detailed in Science, a team led by Kiyotaka Aikawa studied a single, charge-neutral nanoparticle levitating in a periodic intensity pattern formed by the interference of criss-crossed laser beams. Such patterns are known as optical lattices, and they are ideal for testing the quantum mechanical behaviour of small-scale objects because they can levitate the object. This keeps it isolated from other particles and allows it to sustain its fragile quantum state.

After levitating the particle and cooling it to its motional ground state, the team rapidly varied the intensity of the lattice laser. This had the effect of changing the particle’s oscillation frequency, which in turn changed the uncertainty in its momentum. To measure this change (and prove they had demonstrated quantum squeezing), the researchers then released the nanoparticle from the trap and let it propagate for a short time before measuring its velocity. By repeating these time-of-flight measurements many times, they were able to obtain the particle’s velocity distribution.

The telltale sign of quantum squeezing, the physicists say, is that the velocity distribution they measured for the nanoparticle was narrower than the uncertainty in velocity for the nanoparticle at its lowest energy level. Indeed, the measured velocity variance was narrower than that of the ground state by 4.9 dB, which they say is comparable to the largest mechanical quantum squeezing obtained thus far.

“Our system will enable us to realize further exotic quantum states of motions and to elucidate how quantum mechanics should behave at macroscopic scales and become classical,” Aikawa tells Physics World. “This could allow us to develop new kinds of quantum devices in the future.”

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SpaceX successfully completed the final flight of version 2 of Starship on Oct. 13, performing in-flight tests as the company prepares to introduce an upgraded version of the reusable rocket.

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If you stayed awake in science class as a kid, the payoff comes when you get a good laugh out of Freya McGhee’s jokes.

The theoretical physicist Michael Berry from the University of Bristol has won the 2025 Isaac Newton Medal and Prize for his “profound contributions across mathematical and theoretical physics in a career spanning over 60 years”. Presented by the Institute of Physics (IOP), which publishes Physics World, the international award is given annually for “world-leading contributions to physics by an individual of any nationality”.

Born in 1941 in Surrey, UK, Berry earned a BSc in physics from the University of Exeter in 1962 and a PhD from the University of St Andrews in 1965. He then moved to Bristol, where he has remained for the rest of his career.

Berry is best known for his work in the 1980s in which he showed that, under certain conditions, quantum systems can acquire what is known as a geometric phase. He was studying quantum systems in which the Hamiltonian describing the system is slowly changed so that it eventually returns to its initial form.

Berry showed that the adiabatic theorem widely used to describe such systems was incomplete and that a system acquires a phase factor that depends on the path followed, but not on the rate at which the Hamiltonian is changed. This geometric phase factor is now known as the Berry phase.

Over his career Berry, has written some 500 papers across a wide number of topics. In physics, Berry’s ideas have applications in condensed matter, quantum information and high-energy physics, as well as optics, nonlinear dynamics, and atomic and molecular physics. In mathematics, meanwhile, his work forms the basis for research in analysis, geometry and number theory.

Berry told Physics World that the award is “unexpected recognition for six decades of obsessive scribbling…creating physics by seeking ‘claritons’ – elementary particles of sudden understanding – and evading ‘anticlaritons’ that annihilate them” as well as “getting insights into nature’s physics” such as studying tidal bores, tsunamis, rainbows and “polarised light in the blue sky”.

Over the years, Berry has won a wide number of other honours, including the IOP’s Dirac Medal and the Royal Medal from the Royal Society, both awarded in 1990. He was also given the Wolf Prize for Physics in 1998 and the 2014 Lorentz Medal from the Royal Netherlands Academy of Arts and Sciences. In 1996 he received a knighthood for his services to science.

Berry will also be a speaker at the IOP’s International Year of Quantum celebrations on 4 November.

Celebrating success

Berry’s latest honour forms part of the IOP’s wider 2025 awards, which recognize everyone from early-career scientists and teachers to technicians and subject specialists. Other winners include Julia Yeomans, who receives the Dirac Medal and Prize for her work highlighting the relevance of active physics to living matter.

Lok Yiu Wu, meanwhile, receives Jocelyn Bell Burnell Medal and Prize for her work on the development of a novel magnetic radical filter device, and for ongoing support of women and underrepresented groups in physics.

In a statement, IOP president Michele Dougherty congratulated all the winners. “It is becoming more obvious that the opportunities generated by a career in physics are many and varied – and the potential our science has to transform our society and economy in the modern world is huge,” says Dougherty. “I hope our winners appreciate they are playing an important role in this community, and know how proud we are to celebrate their successes.”

The full list of 2025 award winners is available here.

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A network of optical cavities could be used to detect gravitational waves (GWs) in an unexplored range of frequencies, according to researchers in the UK. Using technology already within reach, the team believes that astronomers could soon be searching for ripples in space–time across the milli-Hz frequency band at 10⁻⁵ Hz–1 Hz.

GWs were first observed a decade ago and since then the LIGO–Virgo–KAGRA detectors have spotted GWs from hundreds of merging black holes and neutron stars. These detectors work in the 10 Hz–30 kHz range. Researchers have also had some success at observing a GW background at nanohertz frequencies using pulsar timing arrays.

However, GWs have yet to be detected in the milli-Hz band, which should include signals from binary systems of white dwarfs, neutron stars, and stellar-mass black holes. Many of these signals would emanate from the Milky Way.

Several projects are now in the works to explore these frequencies, including the space-based interferometers LISA, Taiji, and TianQin; as well as satellite-borne networks of ultra-precise optical clocks. However, these projects are still some years away.

Multidisciplinary effort

Joining these efforts was a collaboration called QSNET, which was within the UK’s Quantum Technology for Fundamental Physics (QTFP) programme. “The QSNET project was a network of clocks for measuring the stability of fundamental constants,” explains Giovanni Barontini at the University of Birmingham. “This programme brought together physics communities that normally don’t interact, such as quantum physicists, technologists, high energy physicists, and astrophysicists.”

QTFP ended this year, but not before Barontini and colleagues had made important strides in demonstrating how milli-Hz GWs could be detected using optical cavities.

Inside an ultrastable optical cavity, light at specific resonant frequencies bounces constantly between a pair of opposing mirrors. When this resonant light is produced by a specific atomic transition, the frequency of the light in the cavity is very precise and can act as the ticking of an extremely stable clock.

“Ultrastable cavities are a main component of modern optical atomic clocks,” Barontini explains. “We demonstrated that they have reached sufficient sensitivities to be used as ‘mini-LIGOs’ and detect gravitational waves.”

When such GW passes through an optical cavity, the spacing between its mirrors does not change in any detectable way. However, QSNET results have led to Barontini’s team to conclude that milli-Hz GWs alter the phase of the light inside the cavity. What is more, they conclude that this effect would be detectable in the most precise optical cavities currently available.

“Methods from precision measurement with cold atoms can be transferred to gravitational-wave detection,” explains team member Vera Guarrera. “By combining these toolsets, compact optical resonators emerge as credible probes in the milli-Hz band, complementing existing approaches.”

Ground-based network

Their compact detector would comprise two optical cavities at 90° to each other – each operating at a different frequency – and an atomic reference at a third frequency. The phase shift caused by a passing gravitational wave is revealed in a change in how the three frequencies interfere with each other. The team proposes linking multiple detectors to create a global, ground-based network. This, they say, could detect a GW and also locate the position of its source in the sky.

By harnessing this existing technology, the researchers now hope that future studies could open up a new era of discovery of GWs in the milli-Hz range, far sooner than many projects currently in development.

“This detector will allow us to test astrophysical models of binary systems in our galaxy, explore the mergers of massive black holes, and even search for stochastic backgrounds from the early universe,” says team member Xavier Calmet at the University of Sussex. “With this method, we have the tools to start probing these signals from the ground, opening the path for future space missions.”

Barontini adds, “Hopefully this work will inspire the build-up of a global network of sensors that will scan the skies in a new frequency window that promises to be rich of sources – including many from our own galaxy,”.

The research is described in Classical and Quantum Gravity.

 

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