Physicists at the Chinese Academy of Sciences (CAS) have used diamond-based quantum sensors to uncover what they say is the first unambiguous experimental evidence for the Meissner effect – a hallmark of superconductivity – in bilayer nickelate materials at high pressures. The discovery could spur the development of highly sensitive quantum detectors that can be operated under high-pressure conditions.

Superconductors are materials that conduct electricity without resistance when cooled to below a certain critical transition temperature T_c. Apart from a sharp drop in electrical resistance, another important sign that a material has crossed this threshold is the appearance of the Meissner effect, in which the material expels a magnetic field from its interior (diamagnetism). This expulsion creates such a strong repulsive force that a magnet placed atop the superconducting material will levitate above it.

In “conventional” superconductors such as solid mercury, the T_c is so low that the materials must be cooled with liquid helium to keep them in the superconducting state. In the late 1980s, however, physicists discovered a new class of superconductors that have a T_c above the boiling point of liquid nitrogen (77 K). These “unconventional” or high-temperature superconductors are derived not from metals but from insulators containing copper oxides (cuprates).

Since then, the search has been on for materials that superconduct at still higher temperatures, and perhaps even at room temperature. Discovering such materials would have massive implications for technologies ranging from magnetic resonance imaging machines to electricity transmission lines.

Enter nickel oxides

In 2019 researchers at Stanford University in the US identified nickel oxides (nickelates) as additional high-temperature superconductors. This created a flurry of interest in the superconductivity community because these materials appear to superconduct in a way that differs from their copper-oxide cousins.

Among the nickelates studied, La₃Ni₂O_7-δ (where δ can range from 0 to 0.04) is considered particularly promising because in 2023, researchers led by Meng Wang of China’s Sun Yat-Sen University spotted certain signatures of superconductivity at a temperature of around 80 K. However, these signatures only appeared when crystals of the material were placed in a device called a diamond anvil cell (DAC). This device subjects samples of material to extreme pressures of more than 400 GPa (or 4 × 10⁶ atmospheres) as it squeezes them between the flattened tips of two tiny, gem-grade diamond crystals.

The problem, explains Xiaohui Yu of the CAS’ Institute of Physics, is that it is not easy to spot the Meissner effect under such high pressures. This is because the structure of the DAC limits the available sample volume and hinders the use of highly sensitive magnetic measurement techniques such as SQUID. Another problem is that the sample used in the 2023 study contains several competing phases that could mix and degrade the signal of the La₃Ni₂O_7-δ.

Nitrogen-vacancy centres embedded as in-situ quantum sensors

In the new work, Yu and colleagues used nitrogen-vacancy (NV) centres embedded in the DAC as in-situ quantum sensors to track and image the Meissner effect in pressurized bilayer La₃Ni₂O_7-δ. This newly developed magnetic sensing technique boasts both high sensitivity and high spatial resolution, Yu says. What is more, it fits perfectly into the DAC high-pressure chamber.

Next, they applied a small external magnetic field of around 120 G. Under these conditions, they measured the optically detected magnetic resonance (ODMR) spectra of the NV centres point by point. They could then extract the local magnetic field from the resonance frequencies of these spectra. “We directly mapped the Meissner effect of the bilayer nickelate samples,” Yu says, noting that the team’s image of the magnetic field clearly shows both a diamagnetic region and a region where magnetic flux is concentrated.

Weak demagnetization signal

The researchers began their project in late 2023, shortly after receiving single-crystal samples of La₃Ni₂O_7-δ from Wang. “However, after two months of collecting data, we still had no meaningful results,” Yu recalls. “From these experiments, we learnt that the demagnetization signal in La₃Ni₂O_7-δ crystals was quite weak and that we needed to improve either the nickelate sample or the sensitivity of the quantum sensor.”

To overcome these problems, they switched to using polycrystalline samples, enhancing the quality of the nickelate samples by doping them with praseodymium to make La₂PrNi₂O₇. This produced a sample with an almost pure bilayer structure and thus a much stronger demagnetization signal. They also used shallow NV centres implanted on the DAC cutlet (the smaller face of the two diamond tips).

“Unlike the NV centres in the original experiments, which were randomly distributed in the pressure-transmitting medium and have relatively large ODMR widths, leading to only moderate sensitivity in the measurements, these shallow centres are evenly distributed and well aligned, making it easier for us to perform magnetic imaging with increased sensitivity,” Yu explains.

These improvements enabled the team to obtain a demagnetization signal from the La₂PrNi₂O₇ and La₃Ni₂O_7-δ samples, he tells Physics World. “We found that the diamagnetic signal from the La₂PrNi₂O₇ samples is about five times stronger than that from the La₃Ni₂O_7-δ ones prepared under similar conditions – a result that is consistent with the fact that the Pr-doped samples are of a better quality.”

Physicist Jun Zhao of Fudan University, China, who was not involved in this work, says that Yu and colleagues’ measurement represents “an important step forward” in nickelate research. “Such measurements are technically very challenging, and their success demonstrates both experimental ingenuity and scientific significance,” he says. “More broadly, their result strengthens the case for pressurized nickelates as a new platform to study high-temperature superconductivity beyond the cuprates. It will certainly stimulate further efforts to unravel the microscopic pairing mechanism.”

As well as allowing for the precise sensing of magnetic fields, NV centres can also be used to accurately measure many other physical quantities that are difficult to measure under high pressure, such as strain and temperature distribution. Yu and colleagues say they are therefore looking to further expand the application of these structures for use as quantum sensors in high-pressure sensing.

They report their current work in National Science Review.

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SAN FRANCISCO – Spacedock, a Silicon Valley startup formerly known as Orbital Outpost X, announced plans Aug. 20 for a 2026 in-space demonstration of a universal connector for space systems. Working with launch integrator Oligo Space and radiation-shielding specialist Melagen Labs, Spacedock is preparing to fly its berthing and docking connector, also called Spacedock, in […]

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One hundred years after its birth, quantum mechanics remains one of the most powerful and successful theories in all of science. From quantum computing to precision sensors, its technological impact is undeniable – and one reason why 2025 is being celebrated as the International Year of Quantum Science and Technology.

Yet as we celebrate these achievements, we should still reflect on what quantum mechanics reveals about the world itself. What, for example, does this formalism actually tell us about the nature of reality? Do quantum systems have definite properties before we measure them? Do our observations create reality, or merely reveal it?

These are not just abstract, philosophical questions. Having a clear understanding of what quantum theory is all about is essential to its long-term coherence and its capacity to integrate with the rest of physics. Unfortunately, there is no scientific consensus on these issues, which continue to provoke debate in the research community.

That uncertainty was underlined by a recent global survey of physicists about quantum foundational issues, conducted by Nature (643 1157). It revealed a persistent tension between “realist” views, which seek an objective, visualizable account of quantum phenomena, and “epistemic” views that regard the formalism as merely a tool for organizing our knowledge and predicting measurement outcomes.

Only 5% of the 1100 people who responded to the Nature survey expressed full confidence in the Copenhagen interpretation, which is still prevalent in textbooks and laboratories. Further divisions were revealed over whether the wavefunction is a physical entity, a mere calculation device, or a subjective reflection of belief. The lack of agreement on such a central feature underscores the theoretical fragility underlying quantum mechanics.

The willingness to explore alternatives reflects the intellectual vitality of the field but also underscores the inadequacy of current approaches

More broadly, 75% of respondents believe that quantum theory will eventually be replaced, at least partially, by a more complete framework. Encouragingly, 85% agree that attempts to interpret the theory in intuitive or physical terms are valuable. This willingness to explore alternatives reflects the intellectual vitality of the field but also underscores the inadequacy of current approaches.

Beyond interpretation

We believe that this interpretative proliferation stems from a deeper problem, which is that quantum mechanics lacks a well-defined physical foundation. It describes the statistical outcomes of measurements, but it does not explain the mechanisms behind them. The concept of causality has been largely abandoned in favour of operational prescriptions such that quantum theory works impressively in practice but remains conceptually opaque.

In our view, the way forward is not to multiply interpretations or continue debating them, but to pursue a deeper physical understanding of quantum phenomena. One promising path is stochastic electrodynamics (SED), a classical theory augmented by a random electromagnetic background field, the real vacuum or zero-point field discovered by Max Planck as early as 1911. This framework restores causality and locality by explaining quantum behaviour as the statistical response of particles to this omnipresent background field.

Over the years, several researchers from different lines of thought have contributed to SED. Since our early days with Trevor Marshall, Timothy Boyer and others, we have refined the theory to the point that it can now account for the emergence of features that are considered building blocks of quantum formalism, such as the basic commutator and Heisenberg inequalities.

Particles acquire wave-like properties not by intrinsic duality, but as a consequence of their interaction with the vacuum field. Quantum fluctuations, interference patterns and entanglement emerge from this interaction, without the need to resort to non-local influences or observer-dependent realities. The SED approach is not merely mechanical, but rather electrodynamic.

Coherent thoughts

We’re not claiming that SED is the final word. But it does offer a coherent picture of microphysical processes based on physical fields and forces. Importantly, it doesn’t abandon the quantum formalism but rather reframes it as an effective theory – a statistical summary of deeper dynamics. Such a perspective enables us to maintain the successes of quantum mechanics while seeking to explain its origins.

For us, SED highlights that quantum phenomena can be reconciled with concepts central to the rest of physics, such as realism, causality and locality. It also shows that alternative approaches can yield testable predictions and provide new insights into long-standing puzzles. One phenomenon lying beyond current quantum formalism that we could now test, thanks to progress in experimental physics, is the predicted violation of Heisenberg’s inequalities over very short time periods.

As quantum science continues to advance, we must not lose sight of its conceptual foundations. Indeed, a coherent, causally grounded understanding of quantum mechanics is not a distraction from technological progress but a prerequisite for its full realization. By turning our attention once again to the foundations of the theory, we may finally complete the edifice that began to rise a century ago.

The centenary of quantum mechanics should be a time not just for celebration but critical reflection too.

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Structural chirality refers to the geometric property of objects that are not superimposable on their mirror images, a concept that is central to organic chemistry. In contrast, topological chirality in physics involves quantum properties like spin and is essential for understanding topological edge states. The connection between these two forms of chirality remains an open question.

Traditionally, topological phenomena have been studied in spinful systems, where the presence of spin allows for chiral interactions and symmetry-breaking effects. This new study challenges that paradigm by demonstrating that topological chirality can arise even in spinless systems, purely from the three-dimensional structural arrangement of otherwise featureless units.

The researchers mathematically investigate two types of twisted 3D graphite systems, composed of stacked 2D graphene layers. Importantly, large twist angles were used (21.8^∘). In one configuration, the layers are twisted into a helical screw-like structure, while in the other, the twist angles alternate between layers, forming a periodic chiral pattern. These structural designs give rise to novel topological phases.

A key mechanism underlying these effects is intervalley Umklapp scattering. This scattering captures the chirality of the twisted interfaces and induces a sign-flipped interlayer hopping, by introducing a π-flux lattice gauge field. This field alters the symmetry algebra of the system, enabling the emergence of spinless topological chirality.

This research opens up a new design principle for topological materials. By engineering the spatial patterning of structureless units, researchers can induce topological chirality without relying on spin. This has significant implications for the development of topological photonic and acoustic devices, potentially leading to simpler, more tunable materials for applications in quantum computing, sensing, and waveguiding technologies.

Do you want to learn more about this topic?

Interacting topological insulators: a review by Stephan Rachel (2018)

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In condensed matter physics, topological phase transitions are a key area of research because they lead to unusual and potentially useful states of matter. One example is the Floquet topological insulator, which can switch from a non-topological to a topological phase when exposed to a laser pulse. However, detecting these transitions is difficult due to the extremely fast timescales involved and interference from infrared fields, which can distort the photoelectron signals.

A Chern insulator is a unique material that acts as an insulator in its bulk but conducts electricity along its edges. These edge states arise from the material’s crystal structure of the bulk. Unlike other topological materials, Chern insulators do not require magnetic fields. Their edge conduction is topologically protected, meaning it is highly resistant to defects and noise. This makes them promising candidates for quantum technologies, spintronics, and energy-efficient electronics.

In this study, researchers developed a new method to detect phase changes in Chern insulators. Using numerical simulations, they demonstrated that attosecond x-ray absorption spectroscopy, combined with polarization-dependent dichroism, can effectively reveal these transitions. Their semi-classical approach isolates the intra-band Berry connection, providing deeper insight into how topological edge states form and how electrons behave in these systems.

This work represents a significant advance in topological materials research. It offers a new way to observe changes in quantum materials in real time, expands the use of attosecond spectroscopy from simple atoms and molecules to complex solids, and opens the door to studying dynamic systems like Floquet topological insulators.

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Strong–laser–field physics, non–classical light states and quantum information science by U Bhattacharya, Th Lamprou, A S Maxwell, A Ordóñez, E Pisanty, J Rivera-Dean, P Stammer, M F Ciappina, M Lewenstein and P Tzallas (2023)

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Researchers in China have unveiled an ultrabroadband system that uses the same laser and resonator to process signals at frequencies ranging from below 1 GHz up to more than 100 GHz. The system, which is based on a thin-film lithium niobate resonator developed in 2018 by members of the same team, could facilitate the spread of the so-called “Internet of things” in which huge numbers of different devices are networked together at different frequency bands to avoid interference.

Modern complementary metal oxide semiconductor (CMOS) electronic devices generally produce signals at frequencies of a few GHz. These signals are then often shifted into other frequency bands for processing and transmission. For example, sending electronic signals long distances down silicon optical fibres generally means using a frequency of around 200 THz, as silicon is transparent at the corresponding “telecoms” wavelength of 1550nm.

One of the most popular materials for performing this conversion is lithium niobate. This material has been called “the silicon of photonics” because it is highly nonlinear, allowing optical signals to be generated efficiently at a wide range of frequencies.

In integrated devices, bulk lithium niobate modulators are undesirable. However, in 2018 Cheng Wang and colleagues led by Marko Lončar of Harvard University in Massachusetts, US, developed a miniaturized, thin-film version that used an interferometric design to create a much stronger electro-optic effect in a shorter distance. “Usually, the bandwidth limit is set by the radiofrequency loss,” explains Wang, who is now at the City University of Hong Kong, China. “Being shorter means you can go to much higher frequencies.”

A broadband data transmission system

In the new work, Wang, together with researchers at Peking University in China and the University of California, Santa Barbara in the US, used an optimized version of this setup to make a broadband data transmission system. They divided the output of a telecom-wavelength oscillator into two arms. In one of these arms, optical signal modulation software imprinted a complex amplitude-phase pattern on the wave. The other arm was exposed to the data signal and a lithium niobate microring resonator. The two arms were then recombined at a photodetector, and the frequency difference between the two arms (in the GHz range) was transmitted using an antenna to a detector, where the process was reversed.

Crucially, the offset between the centre frequencies of the two arms (the frequency of the beat note at the photodetector when the two arms are recombined) is determined solely by the frequency shift imposed by the lithium niobate resonator. This can be tuned anywhere between 0.5 GHz and 115 GHz via the thermo-optic effect – essentially, incorporating a small electronic heater and using it to tune the refractive index. The signal is then encoded in modulations of the beat frequency, with additional information imprinted into the phase of the waves.

The researchers say this system is an improvement on standard electronic amplifiers because such devices usually operate in relatively narrow bands. Using them to make large jumps in frequency therefore means that signals need to be shifted multiple times. This introduces cumulative noise into the signal and is also problematic for applications such as robotic surgery, where the immediate arrival of a signal can literally be a matter of life and death.

Internet of things applications

The researchers demonstrated wireless data transfer across a distance of 1.3 m, achieving speeds of up to 100 gigabits per second. In the present setup, they used three different horn antennas to transmit microwaves of different frequencies through free space, but they hope to improve this: “That is our next goal – to get a fully frequency-tuneable link,” says Peking University’s Haowen Shu.

The researchers believe such a wideband setup could be crucial to the development of the “Internet of things” in which all sorts of different electronic devices are networked together without unwanted interference. Atmospheric transparency windows below 6 GHz, where loss is lower and propagation lengths are higher, are likely to be crucial for providing wireless Internet access to rural areas. Meanwhile, higher frequencies – with higher data rates – will probably be needed for augmented reality and remote surgery applications.

Alan Willner, an electrical engineer and optical scientist at the University of Southern California, US, who was not involved in the research, thinks the team is on the right track. “You have lots of spectrum in various radio bands for wireless communications,” he says. “But how are you going to take advantage of these bands to transmit high data rates in a cost-effective and flexible way? Are you going to use multiple different systems – one each for microwave, millimetre wave, and terahertz?  Using one tuneable and reconfigurable integrated platform to cover these bands is significantly better. This research is a great step in that direction.”

The research is published in Nature.

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