Scientists observe Einstein's gravity in the quantum world

Amazing stuff! This could be a breakthrough!

"An international team ... has observed a long-predicted effect of gravity on a falling quantum object for the first time. The result shows that a fundamental principle at the heart of Einstein's theory of gravity remains consistent with the behavior of matter in the quantum world. ...

Now, an international team has performed an experiment that probes the point where they meet. In the study, the researchers observed a distinctive change in the quantum properties of atoms as they fell under gravity. Crucially, the effect they measured is the same one predicted when Einstein's equivalence principle, a cornerstone of his theory of gravity, is applied to a quantum object. 

The equivalence principle states that for an observer in free fall, gravity should locally disappear. ...

At the heart of the experiment is a new apparatus the researchers call the Quantum Galileo Interferometer. It allowed them to do something unusual: effectively split the quantum wave associated with an atom into two paths, hold one in place while allowing the other to fall freely, and then reunite them to see how gravity had changed the falling wave. ...

The experiment ... using clouds of rubidium atoms cooled to just above absolute zero and manipulated close to the surface of a specially designed atom chip. ..."

"... The experimental team ... first used microwave pulses to put the ultracold atoms into a quantum superposition, effectively allowing each atom to travel along two different paths at once. They then used tiny electrical wires on the chip to generate precisely controlled magnetic fields.

One part of the atomic wave responded to this magnetic field, allowing the researchers to apply an upward force that exactly counteracted the downward pull of gravity. In effect, this part was held stationary relative to the laboratory and the Earth. ...

At the end of the fall, the researchers used another precisely controlled magnetic pulse to bring the two parts back together.

When the two waves were reunited, they interfered with each other. That interference allowed the researchers to measure the tiny difference in quantum phase accumulated while one was falling and the other was held still.

The phase measured in the new experiment is the same as the one predicted when Einstein's principle is applied to such a quantum wave. The result therefore provides an experimental connection between quantum physics and Einstein's theory of gravity. ..."

From the abstract:

"The unification of quantum theory and the general theory of relativity, describing gravity, is one of the most important challenges in science.

Einstein’s general theory of relativity is based on the principle of equivalence and has been confirmed to great accuracy for large bodies.

However, in the quantum domain, the equivalence principle has been predicted to take a unique form involving a gauge phase, which is equal, in the context of a measurement on Earth, to the quantum phase of a free-falling wave packet relative to its counterpart wave packet which is static in Earth’s frame.

To measure this phase, we realize a novel cold-atom interferometer in which one wave packet stays static in the laboratory frame while the other is in free fall. The observed relative phase of the wave packets confirms the predicted phase and shows that, in our low energy regime, the equivalence principle may be applied to the quantum domain.

Our observation constitutes a fundamental test of the interface between quantum theory and gravity. The new interferometer also opens the door for further probing of the latter interface, as well as to searches for new physics."

Scientists observe Einstein's gravity in the quantum world

Scientists observe Einstein’s gravity in the quantum world (original news release, Oxford University)

Scientists observe Einstein’s gravity in the quantum world (original news release, Ben Gurion University)

Observation of the quantum phase of free fall and the consistency with the equivalence principle (open access)

The 2D MOT apparatus which feeds the science chamber with cold atoms.

Fig. 1. The QGI experiment to measure the phase accumulation of a free-falling particle.

Is Quantum Entanglement Real? The Ultimate Test

Recommendable!

(236) Is Quantum Entanglement Real? The Ultimate Test | NOVA | PBS - YouTube

Australian scientists have been building the world’s first quantum battery

Good news! This seems to be very preliminary, unpublished research and it refers back to research published already in March of 2026.

"... a device that charges faster the bigger it gets. For now, it only holds a charge for nanoseconds."

"... In March 2026, his team made an important breakthrough when they unveiled what they say is the world's first working quantum battery prototype. ...

latest experiment represents a first tentative step towards a quantum battery that could one day be substituted for conventional ones. However, at present, the prototype battery can only hold a very small amount of energy – a few billion electron volts – for a matter of nanoseconds. ...

Quach says he has in fact already achieved this with a new design he's built, and is now working on a paper to publish the results. It uses "a hybrid structure", he says, involving quantum components to allow super-fast charging with classical layers added in to store the energy for longer.

He also plans to combine many microscopic quantum batteries together to increase their total capacity. ..."

"... One strange feature of the quantum world is what are called “collective effects”. They are what give quantum batteries their unique properties.

Under the right circumstances, the storage units of quantum batteries don’t act individually, but behave collectively. In a counterintuitive twist, this means the units charge faster together than if they were charging alone.

Let’s say your quantum battery has N storage units, and each unit takes one second to charge. Collective effects mean that if all units are charged at once, each unit will take only 1∕√N seconds to charge.

This means that the bigger your quantum battery, the less time it takes to charge. If it doubles in size, charging will take just a little more than half as long. ..."

From the abstract:

"Superextensivity, where the response of a physical system scales super-linearly with size, originates from collective quantum effects and provides a promising route to augment next-generation quantum technologies.

While recent work has demonstrated superextensive behaviour in the coherent dynamics of quantum systems, these effects typically occur on short timescales, prohibiting their practical utility.

In contrast, triggering steady-state superextensive effects in, for example, a generated electric current, remains unexplored despite the immediate impact on photovoltaic technologies.

Here, we utilise a microcavity quantum battery as an experimental platform that superextensively captures light energy and converts it to an electric current via the incorporation of charge transport layers into the resonant microcavity.

This architecture enables, for the first time, a complete quantum battery charge-discharge cycle. We demonstrate that strong light–matter coupling induced by the microcavity leads to superextensive scaling of the steady-state electrical discharging power under low-intensity, incoherent illumination.

Our results provide the first experimental demonstration of superextensive light-to-charge conversion in steady-state, highlighting the feasibility of leveraging strong light–matter coupling for enhanced energy harvesting under low-light conditions."

Wednesday, August 26, 2026 - Join The Flyover

'It's very counterintuitive': The quantum batteries that upend the rules of charging "Scientists have made the world's first quantum battery prototype and, unlike conventional batteries, it charges faster the larger it gets. Could these bizarre devices one day power quantum computing – or even your phone?"

A world-first quantum battery charges faster when it gets bigger – but it’s tiny and only lasts nanoseconds (original news release, but from March 2026) "In quantum batteries, subunits take collective action to charge faster."

Superextensive electrical power from a quantum battery (open access, published March 2026, I blogged here about this paper)

Fig. 1: Composition of the quantum battery tuned for strong light–matter coupling.

Building a superconducting quantum circuit that follows protons on the go

Amazing stuff!

"Researchers ... have created a device that simulates the quantum “tunneling” behavior of protons that occurs in chemistry, a process so common it occurs in everything from photosynthesis to the formation of human DNA.

The advance has the potential to aid researchers across a variety of disciplines, including the development of new solar fuels, pharmaceuticals, and materials. ...

“Our system is so clean and controllable that we could resolve very subtle quantum tunneling effects with it that were unknown to us,” ..."

From the abstract:

"Dissipative tunneling remains a cornerstone effect in quantum mechanics. In chemistry, it plays a crucial role in governing the rates of chemical reactions, often modeled as the motion along the reaction coordinate from one potential well to another. The relative positions of energy levels in these wells strongly influence the reaction dynamics. Chemical research will benefit from a fully adjustable, asymmetric double-well equipped with precise measurement capabilities of the tunneling rates.

In this paper, we show a quantum simulator system that consists of a continuously driven Kerr parametric oscillator with a third-order nonlinearity that can be operated in the quantum regime to create a fully tunable asymmetric double-well. Our experiment leverages a low-noise, all-microwave control system with a high-efficiency readout, based on a tunnel Josephson junction circuit, of the which-well information.

We explore the reaction rates across the landscape of tunneling resonances in parameter space. We uncover two counter-intuitive effects:

(i) a weak asymmetry can significantly decrease the activation rates, even though the well in which the system is initialized is made shallower, and

(ii) the width of the tunneling resonances alternates between narrow and broad lines as a function of the well depth and asymmetry.

We predict by numerical simulations that both effects will also manifest themselves in ordinary chemical double-well systems in the quantum regime.

Our work is a first step for the development of analog molecule simulators of proton transfer reactions based on quantum parametric processes."

Building a superconducting quantum circuit that follows protons on the go | Yale News "A new device that originated at a pair of Yale labs simulates quantum proton “tunneling,” a ubiquitous phenomenon found commonly in chemistry and biology."

Asymmetry Control in a Parametric Oscillator for the Quantum Simulation of Chemical Activation (open access)

Fig. 1 Experimental setup. (a) Rendering of the half-aluminum, half-copper sample package containing two sapphire chips magnified in (b).

Pure classical physics can explain quantum phenomena, study shows

Amazing stuff!

"A reformulation of the classical Hamilton-Jacobi equation, incorporating density and multiple least-action paths, can exactly reproduce quantum phenomena such as the double-slit experiment, quantum tunneling, and hydrogen atom wave functions. This approach mathematically bridges classical and quantum mechanics, showing that quantum behavior can be computed using classical principles without approximations."

" ... MIT scientists have now shown that certain mathematical ideas from everyday classical physics can be used to describe the often weird and nonintuitive behavior that occurs at the quantum, subatomic scale.

In a paper appearing today in the journal Proceedings of the Royal Society A Mathematical Physical and Engineering Science, the team shows that the motion of a quantum object can be calculated by applying an idea from classical physics known as "least action." With their new formulation, they show they can arrive at exactly the same solution as the Schrödinger equation—the main description of quantum mechanics—for a number of textbook quantum-mechanical scenarios, including the double-slit experiment and quantum tunneling. ..."

From the abstract:

"We show that the Schrödinger equation can be solved exactly based only on classical least action.

Fundamental postulates of quantum mechanics can in turn be derived directly from this construction. The results extend to the relativistic Klein-Gordon, Pauli, and Dirac equations, and suggest a smooth transition between physics across scales. 

Most quantum mechanics problems have classical versions which involve multiple least action solutions. The associated classical multipaths stem either from the initial position or momentum distribution, or from branch points, generated, e.g. by a multiply connected manifold (double slit experiment), by spatial inequality constraints (particle in a box), or by a singularity (Coulomb potential). We show that the exact Schrödinger wave function  can be constructed by combining this classical multi-valued action with the classical density ⁠, computed analytically from  along each extremal action path.

The construction is general and does not involve any semi-classical approximation.

Quantum wave collapse at measurement can be derived from the classical density change. Entanglement corresponds to a sum of classical particle actions mapping to a tensor product of spinors. The results also provide a simpler computational alternative to Feynman path integrals, as they use only a minimal subset of classical paths."

Classical physics can explain quantum weirdness, study shows

On computing quantum waves exactly from classical action (open access)

New study bridges the worlds of classical and quantum physics (original news release) "The weird quantum behavior of subatomic particles can be understood through everyday classical ideas, MIT researchers show."

On computing quantum waves exactly from classical and relativistic action (prepint, first published 5/10/2024, open access)

Solid-state quantum sensors can measure several properties at once

Amazing stuff! This could be a breakthrough!

"A special class of sensors leverages quantum properties to measure tiny signals at levels that would be impossible using classical sensors alone. Such quantum sensors are currently being used to study the inner workings of cells and the outer depths of our universe.

Particularly promising are solid-state quantum sensors, which can operate at room temperature. Unfortunately, most solid-state quantum sensors today only measure one physical quantity at a time — such as the magnetic field, temperature, or strain in a material. Trying to measure both the magnetic field and temperature of a material at the same time causes their signals to get mixed up and measurements to become unreliable.

Now, ... researchers have created a way to simultaneously measure multiple physical quantities with a solid-state quantum sensor. They achieved this by exploiting entanglement, where particles become correlated into a single quantum state. In a new paper, the team demonstrated its approach in a commonly used quantum sensor at room temperature, measuring the amplitude, frequency, and phase of a microwave field in a single measurement. They also showed the approach works better than sequentially measuring each property or using traditional sensors.

The researchers say the approach could enable quantum sensors that can deepen our understanding of the behavior of atoms and electrons inside materials and living systems like cancer cells. ...

Although the researchers say their sensor didn’t measure each quantity at the highest possible precision, in future work they plan to explore if their approach can achieve higher precision for each parameter. ..."

From the abstract:

"Quantum multiparameter estimation promises to extend quantum advantage to the simultaneous high-precision measurements of multiple physical quantities. However, realizing this capability in practical quantum sensors under realistic conditions remains challenging due to intrinsic system imperfections.

Here, we experimentally demonstrate multiparameter estimation using a nitrogen-vacancy (NV) center in diamond, a widely adopted solid-state quantum sensor.

Leveraging electronic-nuclear spin entanglement and optimized Bell-state measurement at room temperature, we simultaneously estimate the amplitude, detuning, and phase of a microwave drive from a single measurement sequence.

Despite practical constraints, our results achieve linear sensitivity scaling for all parameters with respect to interrogation time. This work bridges the gap between foundational quantum estimation theory and real-world quantum sensing, opening pathways toward enhanced multiparameter quantum sensors suitable for diverse scientific and technological applications."

Multitasking quantum sensors can measure several properties at once | MIT News | Massachusetts Institute of Technology "The devices represent a key step toward practical quantum sensing, with applications in biomedical sensing, materials characterization, and more."

Entanglement-Assisted Multiparameter Estimation with a Solid-State Quantum Sensor (open access)

Fig. 1. Principles of multiparameter estimation based on a single NV center in diamond.

World's first proof-of-concept quantum battery prototype

Good news!

"Australian researchers have created the world’s first proof-of-concept quantum battery, opening research into a new generation of energy storage devices.

Quantum batteries don’t yet exist. They would store and discharge energy but unlike current batteries they wouldn’t be based on chemical reactions. Quantum batteries, instead, use principles like quantum superposition and entanglement to store and discharge energy between discrete energy states in subcells within the battery.

These devices would not be subject to chemical and thermal wear and promise incredibly fast charging times which gets even faster as the quantum batteries get bigger.

A major issue with current quantum battery designs, however, is that they discharge within nanoseconds. ...

“My ultimate ambition is a future where we can charge electric cars much faster than fuel petrol cars, or charge devices over long distances wirelessly,” says senior author James Quach who leads quantum science and technologies science research at CSIRO. ..."

"... “Our findings confirm a fundamental quantum effect that's completely counterintuitive: quantum batteries charge faster as they get larger.” ..."

From the abstract:

"Superextensivity, where the response of a physical system scales super-linearly with size, originates from collective quantum effects and provides a promising route to augment next-generation quantum technologies.

While recent work has demonstrated superextensive behaviour in the coherent dynamics of quantum systems, these effects typically occur on short timescales, prohibiting their practical utility.

In contrast, triggering steady-state superextensive effects in, for example, a generated electric current, remains unexplored despite the immediate impact on photovoltaic technologies.

Here, we utilise a microcavity quantum battery as an experimental platform that superextensively captures light energy and converts it to an electric current via the incorporation of charge transport layers into the resonant microcavity. This architecture enables, for the first time, a complete quantum battery charge-discharge cycle.

We demonstrate that strong light–matter coupling induced by the microcavity leads to superextensive scaling of the steady-state electrical discharging power under low-intensity, incoherent illumination.

Our results provide the first experimental demonstration of superextensive light-to-charge conversion in steady-state, highlighting the feasibility of leveraging strong light–matter coupling for enhanced energy harvesting under low-light conditions."

World's first quantum battery prototype | News | ConnectSci

Australian scientists achieve energy storage and quantum battery breakthrough (original news release) "Researchers develop the first quantum battery that could pave the way for long- distance charging of devices and super-fast charging of electric cars."

Superextensive electrical power from a quantum battery (open access)

Fig. 1: Composition of the quantum battery tuned for strong light–matter coupling.

Fig. 2: Superextensive charging dynamics.

CSIRO’s clean lab for engineering prototype quantum batteries

New state of matter discovered in a quantum material

Amazing stuff!

"At TU Wien, researchers have discovered a state in a quantum material that had previously been considered impossible. The definition of topological states should be generalized. ...

Now, a research team at TU Wien has shown that such materials can nevertheless exhibit topological properties—even though these have so far been explained using particle-like behavior. This demonstrates that topological states are more general than previously thought: two seemingly contradictory concepts turn out to be compatible. ...

However, there are also situations in which this picture appears to break down completely and the charge carriers lose their particle-like character. This seems to happen in the material composed of cerium, ruthenium and tin (CeRu₄Sn₆), which has now been investigated at TU Wien at extremely low temperatures. “Near absolute zero, it exhibits a specific type of quantum-critical behavior,” ... “The material fluctuates between two different states, as if it cannot decide which one it wants to adopt. In this fluctuating regime, the quasiparticle picture is thought to lose its meaning.” ...

Indeed, at extremely low temperatures—less than one degree above absolute zero. .. observed behavior that clearly indicates the presence of topological states: a spontaneous (anomalous) Hall effect. In the Hall effect, charge carriers are normally deflected by a magnetic field. However, this deflection can also arise from topological effects, even in the absence of any external magnetic field. What is particularly remarkable is that the charge carriers behave as if they were particles, even though the particle picture seems to fail in this material. ...

The team refers to the newly discovered state as an emergent topological semimetal  ... a new theoretical model capable of combining the phenomena of quantum criticality and topology.

“In fact, it turns out that a particle picture is not required to generate topological properties,” ... “The concept can indeed be generalized—the topological distinctions then emerge in a more abstract, mathematical way. And more than that: our experiments suggest that topological properties can even arise because particle-like states are absent.” ..."

From the abstract:

"The electronic topology of a material is generally described by its Bloch states and the associated band structure, and can be altered by electron–electron interactions.

In metallic systems, the interactions are usually treated through the concept of quasiparticles. Here we investigate what happens if no well-defined quasiparticles are present and show that a topological semimetal phase can emerge from the material’s quantum critical state.

Using the non-centrosymmetric heavy-fermion compound CeRu4Sn6, which is intrinsically quantum critical, we show that the topological phase exhibits a dome structure as a function of the magnetic field and pressure. To understand these results, we study a Weyl–Kondo semimetal model at a Kondo destruction quantum critical point.

Indeed, it exhibits features in the spectral function that can define topological crossings beyond the quasiparticle picture. Our results outline the importance of the interplay of quantum critical fluctuations and symmetry to search for other emergent topological phases."

New state of matter discovered in a quantum material

Quantum Physics: New State of Matter Discovered (original news release) "At TU Wien, researchers have discovered a state in a quantum material that had previously been considered impossible. The definition of topological states should be generalized."

Emergent topological semimetal from quantum criticality (open access)

Fig. 5: Kondo destruction quantum criticality nucleating a Weyl–Kondo semimetal.

New state of matter discovered in a quantum material

Amazing stuff, however under extreme conditions! How esoteric is this research?

"At TU Wien, researchers have discovered a state in a quantum material that had previously been considered impossible. The definition of topological states should be generalized. ...

Even more modern approaches are based on this particle picture—such as the concept of topological states, whose discovery was honored with the Nobel Prize in Physics in 2016. However, there are materials in which the particle picture completely breaks down ... In such cases, it no longer makes sense to think of electrons as small particles with a well-defined position or a unique velocity.

Now, a research team at TU Wien has shown that such materials can nevertheless exhibit topological properties—even though these have so far been explained using particle-like behavior. This demonstrates that topological states are more general than previously thought: two seemingly contradictory concepts turn out to be compatible. ...

the charge carriers [electrons] lose their particle-like character. This seems to happen in the material composed of cerium, ruthenium and tin (CeRu₄Sn₆), which has now been investigated at TU Wien at extremely low temperatures. “Near absolute zero, it exhibits a specific type of quantum-critical behavior,”  ... “The material fluctuates between two different states, as if it cannot decide which one it wants to adopt. In this fluctuating regime, the quasiparticle picture is thought to lose its meaning.” ..."

From the abstract:

"The electronic topology of a material is generally described by its Bloch states and the associated band structure, and can be altered by electron–electron interactions.

In metallic systems, the interactions are usually treated through the concept of quasiparticles. Here we investigate what happens if no well-defined quasiparticles are present and show that a topological semimetal phase can emerge from the material’s quantum critical state.

Using the non-centrosymmetric heavy-fermion compound CeRu4Sn6, which is intrinsically quantum critical, we show that the topological phase exhibits a dome structure as a function of the magnetic field and pressure.

To understand these results, we study a Weyl–Kondo semimetal model at a Kondo destruction quantum critical point. Indeed, it exhibits features in the spectral function that can define topological crossings beyond the quasiparticle picture. Our results outline the importance of the interplay of quantum critical fluctuations and symmetry to search for other emergent topological phases."

New state of matter discovered in a quantum material

Quantum Physics: New State of Matter Discovered (original news release) "At TU Wien, researchers have discovered a state in a quantum material that had previously been considered impossible. The definition of topological states should be generalized."

Emergent topological semimetal from quantum criticality (open access)

Fig. 5: Kondo destruction quantum criticality nucleating a Weyl–Kondo semimetal.

Heisenberg Made a Discovery in 1925. We Still Can't Explain It with Matt O'Dowd

Very recommendable!

Experimental proof shows quantum world is even stranger than previously thought

Amazing stuff!

"... To see whether any system is behaving classically, scientists use a mathematical test called the Leggett-Garg inequality (LGI). Classical systems always obey the LGI limit while quantum systems violate it, proving they are non-classical.

Breaking a quantum limit

But even in quantum systems, this violation has a limit called the temporal Tsirelson's bound (TTB). In this research, scientists wanted to see if they could break the TTB limit and find even more extreme forms of quantum weirdness.

... theorized that a new kind of quantum motion, in which a particle follows two distinct sets of movement instructions simultaneously, could be powerful enough to break the TTB limit. They called this superposition of unitaries.

The team tested their idea in an NMR (nuclear magnetic resonance) machine, which let them control a qubit (the basic building block of quantum information). In this experiment, the qubit was a carbon nucleus within a molecule. The researchers designed a precise quantum circuit using a helper particle (an ancillary qubit) to make the qubit follow two sets of instructions at the same time. Specifically, they combined two different kinds of magnetic rotation on the qubit.

Results and applications

When the system evolved under this new combined motion, the changes were immediate and dramatic. The researchers measured the LGI violation and found it had smashed the TTB limit, confirming a new level of quantum weirdness. ..."

From the abstract:

"The violation of Leggett-Garg inequality (LGI) indicates general temporal correlations in quantum systems that cannot be explained classically.

Under unitary dynamics and projective measurements, the violation of LGI is restricted up to the temporal Tsirelson’s bound (TTB).

Here, we consider superposition of unitary time evolutions and find them to produce an enhancement in the violation of LGI beyond the TTB, growing monotonically with increasing superposition.

We experimentally realize superposition of unitaries in NMR systems and demonstrate this enhanced violation.

In the presence of noise, such superposition of unitaries remarkably extend the time of LGI violation, showcasing improved robustness against decoherence.

This opens up possibilities of employing such nontrivial dynamical maps for robust quantum control, along with provoking research on characterizing correlations in general sequential measurement scenarios."

Experimental proof shows quantum world is even stranger than previously thought

Extreme Violations of Leggett-Garg Inequalities for a System Evolving under Superposition of Unitaries (no public access)

Enhanced non-macrorealism: Extreme violations of Leggett-Garg inequalities for a system evolving under superposition of unitaries (preprint, open access)

Diamond defects, now in pairs, reveal hidden fluctuations in the quantum world

Amazing stuff! This could be huge! 

"Now ... researchers have developed a diamond-based quantum sensor that reveals rich new information about magnetic phenomena at this minute scale. The technique uncovers fluctuations that are beyond the reach of existing instruments and provides key insight into materials such as graphene and superconductors. Superconductors have enabled today’s most advanced medical imaging tools and form the basis of hoped-for technologies like lossless power lines and levitating trains. ...

the team reported roughly 40-times greater sensitivity than previous techniques. ...

That enables unprecedented measurement and reveals details about magnetic fluctuations that hide in the statistical data of more conventional approaches. ...

Her team’s new technique is based on engineered defects near the surface of a lab-grown diamond. These diamonds, about the size of a large flake of sea salt ... one missing atom in a lattice of billions. But because those defects interact strongly with magnetic fields, and because they can be carefully engineered, they make excellent magnetic sensors.

Typically, these sensors are treated as individual points in space. In this latest advance, de Leon and her team built a system that implants two of these defects extremely close together, allowing the defects to interact in quantum-mechanical ways  ..."

From the abstract:

"Nitrogen vacancy (NV) centres in diamond are widely deployed as local magnetic sensors, using single-qubit control to measure both time-averaged fields and noise with nanoscale spatial resolution1.

Moving beyond single qubits to multi-qubit control enables new sensing modalities such as measuring nonlocal spatiotemporal correlators or using entangled states to enhance measurement sensitivity.

Here we describe protocols for using optically unresolved NV centre pairs and nuclear spins as multi-qubit sensors for measuring correlated noise at nanometre length scales.

For noninteracting NV centres, we implement a phase-cycling protocol that disambiguates magnetic correlations from variance fluctuations, leveraging the presence of a third qubit, a 13C nucleus, to effect coherent single-NV spin flips and enable phase cycling even for co-aligned NV centres that are spectrally unresolved. For length scales around 10 nm, we create maximally entangled Bell states through dipole–dipole coupling between two NV centres and use these entangled states to directly read out the magnetic field correlation, rather than reconstructing it from independent measurements of unentangled NV centres.

Importantly, this changes the scaling of sensitivity with readout noise from quadratic to linear.

For conventional off-resonant readout of the NV centre spin state (for which the readout noise is roughly 30 times the quantum projection limit), this results in more than an order of magnitude improvement in sensitivity. Finally, we demonstrate methods for detecting high spatial- and temporal-resolution correlators with pairs of strongly interacting NV centres."

Diamond defects, now in pairs, reveal hidden fluctuations in the quantum world - Princeton Engineering "In spaces smaller than a wavelength of light, electric currents jump from point to point and magnetic fields corkscrew through atomic lattices in ways that defy intuition. Scientists have only ever dreamed of observing these marvels directly."

Multi-qubit nanoscale sensing with entanglement as a resource (no public access)

Multi-qubit nanoscale sensing with entanglement as a resource (preprint, open access)

Credits: Quantensensor zeigt Magnetfelder, die bisher niemand sehen konnte "Neue Quantensensor-Technologie nutzt verschränkte Diamant-Defekte, um unsichtbare magnetische Phänomene in Supraleitern und Graphen zu messen."

Nathalie de Leon, a leader in diamond-based quantum sensing technologies, led the development of a technique that uncovers previously invisible magnetic fluctuations that are key to understanding quantum materials like graphene and superconductors.

Precision sensing experiment bypasses Heisenberg's uncertainty principle

Amazing stuff! This could be a breakthrough!

"The new research has demonstrated how scientists can precisely measure position and momentum of a particle at the same time. The researchers hope this new method could help develop ultra-precise sensor technology which may be used to improve navigation, medicine and astronomy. ...

The approach was first outlined theoretically in 2017, with Tan’s team now performing the first experimental demonstration. The team were able to conduct the experiment using a technological approach they had engineered in a previous study for error-corrected quantum computers. ...

The team used the microscopic vibrational motion of a trapped ion to implement the sensing protocol. These ions were prepared in ‘grid states’, the type of states used in error-corrected quantum computing.

These grid states are then able to measure tiny signals that indicate position and momentum. The measurements were collected with a precision better than the best achieved using only classical sensors. ..."

"... The ability to detect extremely small changes is important across science and technology. Ultra-precise quantum sensors could sharpen navigation in environments where GPS doesn’t work (such as submarines, underground or spaceflight); enhance biological and medical imaging; monitor materials and gravitational systems; or probe fundamental physics. ..."

From the abstract:

"Precise measurements underpin scientific and technological advancements. Quantum mechanics provides an avenue to enhance precision, but it comes with a restriction: Incompatible observables, such as position and momentum, cannot be simultaneously measured to arbitrary accuracy as decreed by Heisenberg’s uncertainty principle. 

This restriction can be bypassed by instead measuring commuting modular observables, which are counterparts to the naturally incompatible observables. Here, we measure modular observables to estimate small changes in position and momentum with a single-mode multiparameter sensor.

We deterministically prepare grid states in the mechanical motion of a trapped ion and demonstrate uncertainties in position and momentum below the standard quantum limit (SQL).

Further, we examine another pair of incompatible observables—number and phase. We prepare a different resource—number-phase states—and demonstrate a metrological gain over the SQL.

These results introduce previously unidentified measurement capabilities unavailable to classical systems and mark a substantial step in quantum metrology."

Experiment bypasses Heisenberg's uncertainty principle

Scientists sidestep Heisenberg uncertainty principle in precision sensing experiment (original news release) "Foundational research opens pathway for next-generation quantum sensors."

Quantum-enhanced multiparameter sensing in a single mode (open access)

Fig. 1. Multiparameter quantum enhanced sensing.

Famous double-slit experiment holds up at the single atom level

Amazing stuff!

"MIT physicists have performed an idealized version of one of the most famous experiments in quantum physics. Their findings demonstrate, with atomic-level precision, the dual yet evasive nature of light. They also happen to confirm that Albert Einstein was wrong about this particular quantum scenario. ...

Scientists have since carried out multiple versions of the double-slit experiment, and they have all, to various degrees, confirmed the validity of the quantum theory formulated by Bohr. Now, MIT physicists have performed the most “idealized” version of the double-slit experiment to date. Their version strips down the experiment to its quantum essentials. They used individual atoms as slits, and used weak beams of light so that each atom scattered at most one photon. By preparing the atoms in different quantum states, they were able to modify what information the atoms obtained about the path of the photons. The researchers thus confirmed the predictions of quantum theory: The more information was obtained about the path (i.e. the particle nature) of light, the lower the visibility of the interference pattern was. ..."

From the abstract:

"We study light scattering of single atoms in free space and discuss the results in terms of atom-photon entanglement and which-way information.

Using ultracold atoms released from an optical lattice, we realize a Gedanken experiment which interferes single photons scattering off of Heisenberg uncertainty-limited wavepackets.

We unify the free-space and trapped-atom pictures by measuring the light scattered during wavepacket expansion and show the coherence properties of the scattered light is independent of the presence of the trap. Our experiment demonstrates the potential of using atomic Mott insulators to create single-atom wavepackets for fundamental studies."

Famous double-slit experiment holds up when stripped to its quantum essentials | MIT News | Massachusetts Institute of Technology "MIT physicists confirm that ... light has two identities that are impossible to see at once."

Coherent and Incoherent Light Scattering by Single-Atom Wave Packets (no public access)

Coherent and incoherent light scattering by single-atom wavepackets (preprint, open access)

Physicists discover new state of quantum matter

Amazing stuff!

"... This new phase is like a liquid composed of electrons and their counterparts, known as "holes," spontaneously pairing and forming exotic states known as excitons. Unusually, the electrons and holes spin together in the same direction. ...

as his team applied the magnetic field, the "material's ability to carry electricity suddenly drops, showing that it has transformed into this exotic state," ... "This discovery is important because it may allow signals to be carried by spin rather than electrical charge, offering a new path toward energy-efficient technologies like spin-based electronics or quantum devices."

Unlike conventional materials used in electronics, this new quantum matter isn't affected by any form of radiation ..."

From the abstract:

"More than 50 years ago, excitonic insulators formed by the pairing of electrons and holes due to Coulomb interactions were first predicted ... 

Since then, excitonic insulators have been observed in various classes of materials, including quantum Hall bilayers, graphite, transition metal chalcogenides, and more recently in moiré superlattices. In these excitonic insulators, an electron and a hole with the same spin bind together, and the resulting exciton is a spin singlet. Here, we report the experimental observation of a spin-triplet excitonic insulator in the ultra-quantum limit of a three-dimensional topological material HfTe5. We observe that the spin-polarized zeroth Landau bands dispersing along the field direction cross each other beyond a characteristic magnetic field in HfTe5, forming the one-dimensional Weyl mode. Transport measurements reveal the emergence of a gap of about 2⁢5⁢0  μ⁢eV when the field surpasses a critical threshold.

By performing the material-specific modeling, we identify this gap as a consequence of a spin-triplet exciton formation, where electrons and holes with opposite spin form bound states, and the translational symmetry is preserved.

The system reaches charge neutrality following the gap opening, as evidenced by the zero Hall conductivity over a wide magnetic field range (10–72 T). Our finding of the spin-triplet excitonic insulator paves the way for studying novel spin transport including spin superfluidity, spin Josephson currents, and Coulomb drag of spin currents in analogy to the transport properties associated with the layer pseudospin in quantum Hall bilayers."

Physicists discover new state of quantum matter

UC Irvine scientists discover new state of quantum matter (original news release) "The research can help make new quantum technologies primed for deep-space travel"

Possible Spin-Triplet Excitonic Insulator in the Ultraquantum Limit of HfTe5 (no public access)

Spin-Triplet Excitonic Insulator in the Ultra-Quantum Limit of HfTe5 (preprint, open access)

Quantum Energy Teleportation is REAL! with Matt O'Dowd

Recommendable!

Quantum surprise: Matter mediates ultrastrong coupling between light particles using 3D photonic-crystal cavities

Amazing stuff!

"A team ... researchers has developed a new way to control light interactions using a specially engineered structure called a 3D photonic-crystal cavity. Their work ... lays the foundation for technologies that could enable transformative advancements in quantum computing, quantum communication and other quantum-based technologies.

an optical cavity ... a tailored structure that traps light between reflective surfaces, allowing it to bounce around in specific patterns.

These patterns with discrete frequencies are called cavity modes, and they can be used to enhance light-matter interactions, making them potentially useful in quantum information processing, developing high-precision lasers and sensors and building better photonic circuits and fiber-optic networks. ...

built a complex 3D optical cavity and used it to study how multiple cavity modes interact with a thin layer of free-moving electrons exposed to a static magnetic field. The key question guiding their investigation was what happens when multiple cavity modes interact with the electrons simultaneously. ...

leads to strong coupling between light and matter, creating quantum superposition states so-called polaritons.” ...

If the interaction binding photons and electrons into polaritons is extremely intense to the point where the exchange of energy between light and matter happens so fast it resists dissipation a new regime comes into effect known as ultrastrong coupling. ... describes an unusual mode of interaction between light and matter where the two become deeply hybridized ..."

From the abstract:

"Recent theoretical studies have highlighted how spatially varying cavity electromagnetic fields enable novel cavity quantum electrodynamics phenomena, such as the Dicke superradiant phase transition.

Three-dimensional photonic-crystal cavities, which exhibit discrete in-plane translational symmetry, overcome this limitation, but fabrication challenges have hindered the achievement of strong coupling.

Here, we demonstrate multimode ultrastrong coupling between cavity modes of a three-dimensional photonic-crystal cavity at terahertz frequencies and the cyclotron resonance of a Landau-quantized two-dimensional electron gas in gallium arsenide. The multimode coupling depends on the spatial profiles of the cavity modes, resulting in distinct coupling scenarios based on probe polarization.

Our results align with an extended multimode Hopfield model that accounts for spatial field variations.

Guided by the model, we discuss possible strong ground-state correlations between cavity modes and introduce relevant figures of merit for multimode ultrastrong coupling. Our findings highlight the crucial role of spatial inhomogeneity in multimode ultrastrong coupling."

Quantum surprise: Matter mediates ultrastrong coupling between light particles

Rice scientists uncover quantum surprise: Matter mediates ultrastrong coupling between light particles (original news release)

Multimode ultrastrong coupling in three-dimensional photonic-crystal cavities (open access)

Fig. 1: The 3D-PCC [photonic-crystal cavities].

Scientists observe exotic superradiant quantum phase once thought impossible

Amazing stuff!

"A team ... researchers reported the first direct observation of a surprising quantum phenomenon predicted over half a century ago, opening pathways for revolutionary applications in quantum computing, communication, and sensing.

Known as a superradiant phase transition (SRPT), the phenomenon occurs when two groups of quantum particles begin to fluctuate in a coordinated, collective way without any external trigger, forming a new state of matter.

The discovery was made in a crystal composed of erbium, iron, and oxygen that was cooled to minus 457 Fahrenheit and exposed to a powerful magnetic field of up to 7 tesla (over 100,000 times stronger than Earth's magnetic field) ..."

From the abstract:

"Two-level atoms ultrastrongly coupled with single-mode cavity photons are predicted to exhibit a quantum phase transition, entering a phase in which both the atomic polarization and the photonic field are finite even without external driving.

However, this phenomenon, the superradiant phase transition (SRPT), is forbidden by a no-go theorem due to the existence of the diamagnetic term.

Here, we present spectroscopic evidence for a magnonic SRPT in ErFeO3, where the role of the photonic mode (two-level atoms) in the photonic SRPT is played by an Fe3+ magnon mode (Er3+ spins). 

The absence of the diamagnetic term in the Fe3+-Er3+ exchange coupling ensures that the no-go theorem does not apply.

Ultrabroadband terahertz and gigahertz magnetospectroscopy experiments revealed the signatures of the SRPT in thermal equilibrium, a kink and a softening, respectively, of two spin-magnon hybridized modes at the critical point.

Systems near this phase are expected to harbor large-scale squeezing, which will potentially provide a route to next-generation quantum technologies."

Scientists observe exotic quantum phase once thought impossible

Scientists observe exotic quantum phase once thought impossible (original news release) "Discovery in a magnetic crystal could enable breakthroughs in quantum tech"

Observation of the magnonic Dicke superradiant phase transition (open access)

Fig. 1. Comparison between a light-matter system and a magnon-spin system for the Dicke SRPT.

Fig. 2. Spectroscopic evidence for the magnonic SRPT in ErFeO3.

Researchers discover a new type of quantum entanglement

Amazing stuff!

"... Quantum entanglement has been demonstrated so far for a wide variety of particles and for their various properties.

For photons, particles of light, entanglement can exist for their direction of travel, frequency (color), or the direction in which their electric field points. It can also exist for properties that are harder to imagine, such as angular momentum. ...

In a study published in the journal Nature, the Technion researchers discovered that it is possible to entangle photons in nanoscale systems that are a thousandth the size of a hair, but the entanglement is not carried out by the conventional properties of the photon, such as spin or trajectory, but only by the total angular momentum. ..."

From the abstract:

"Photons can carry angular momentum, which is conventionally attributed to two constituents—spin angular momentum (SAM), which is an intrinsic property related to the polarization, and orbital angular momentum (OAM), which is related to the photon spatial distribution.

In paraxial optics, these two forms of angular momentum are separable, such that entanglement can be induced between the SAM and the OAM of a single photon or of different photons in a multi-photon state.

In nanophotonic systems, however, the SAM and the OAM of a photon are inseparable, so only the total angular momentum (TAM) serves as a good quantum number.

Here we present the observation of non-classical correlations between two photons in the near-field regime, giving rise to entanglement related to the TAM.

We entangle those nanophotonic states by coupling photon pairs to plasmonic modes and use quantum imaging techniques to measure their correlations.

We observe that entanglement in TAM leads to a completely different structure of quantum correlations of photon pairs, compared with entanglement related to the two constituent angular momenta.

This work paves the way for on-chip quantum information processing using the TAM of photons as the encoding property for quantum information."

Researchers discover a new type of quantum entanglement

Technion Researchers Discover a New Type of Quantum Entanglement (original news release) "A groundbreaking study from the Technion unveils a newly discovered form of quantum entanglement in the total angular momentum of photons confined in nanoscale structures – just a thousandth the width of a human hair. This discovery could play a key role in the future miniaturization of quantum communication and computing components"

Near-field photon entanglement in total angular momentum (no public access)

Theoretical physicists completely determine the statistics of quantum entanglement

Amazing stuff!

"For the first time, theoretical physicists ... have completely determined the statistics that can be generated by a system using quantum entanglement. This achievement paves the way for exhaustive test procedures for quantum devices. ..."

"... An entangled system comprises two parts that are inextricably linked. When these subsystems are measured, this link appears in the frequencies of the observed results. A signature of the quantum regime par excellence, these statistics are a foundation of the growing field of quantum information. Until now, however, statistics derived from measurements on entangled states have always resisted analysis. By identifying all the frequencies needed to reconstruct the description of the measured quantum system, this work presents the first complete and explicit description of a set of quantum statistics.

This result has both fundamental and applied significance. Indeed, the type of reconstruction obtained forms the basis of the most advanced validation methods for quantum devices. This work paves the way for new, more comprehensive test procedures for quantum devices. At the same time, by determining the extent of quantum statistics, this result identifies the limits of quantum physics itself. It thus informs us about the scope of quantum theory and offers new perspectives for better understanding it."

From the abstract:

"In any experimental setting, quantum physics provides the statistical distributions that the observed outcomes are expected to follow. The set formed by all these distributions contains the imprint of quantum theory and captures some of its core properties. So far, only partial explicit descriptions of this set have been found for Bell-type settings in which entangled states can be shared and measured by independent observers.

Here we obtain the complete explicit and analytical description of a full set of quantum statistics in terms of its extremal points. This is made possible by finding all bipartite quantum states and pairs of binary measurements that can be self-tested, that is, reconstructed from empirical statistics only. Our description precisely reveals some of the extent and limitations of quantum theory."

Theoretical physicists completely determine the statistics of quantum entanglement

Quantum Statistics (original news release) "In a new paper ... provide an answer to a 40-year-old open question about the scope of quantum entanglement."

Quantum statistics in the minimal Bell scenario (no public access)