Lifeboat Foundation: Safeguarding Humanity
Toggle light / dark theme

Blog

Category: quantum physics

Quantum experiment shows events may have no fixed order

For the first time, a team of physicists in Austria has carried out an experiment that appears to verify the principle of indefinite causal order: an idea that suggests that timelines of events can exist in multiple orders at the same time. Led by Carla Richter at the Vienna Center for Quantum Science and Technology, the researchers hope their result could finally allow physicists to verify a key prediction of quantum theory. The results have been published in PRX Quantum.

The basic principle of cause and effect underpins everything that happens in the classical world: for an event to occur, it must be triggered by another event in its past. Yet in the quantum world, physicists have long suspected that these rules may not always apply.

Just as quantum particles can exist in superpositions of multiple states which collapse to a single outcome when measured, indefinite causal order suggests something similar may apply to entire sequences of events. Until a measurement is made, multiple orders of cause and effect can exist in superposition.

Tiny LED design could power next-generation technology

From 3D movie screens to augmented-reality devices, many modern technologies rely on our ability to manipulate light. Doing so in a cost-effective and efficient way, however, is often a formidable task. In an article published in Optics Letters, researchers from the University of Osaka announced a new light-emitting diode (LED) design that may help shrink complex optical systems into much smaller devices. The LED produces circularly polarized light using a built-in nanostructured surface, eliminating the need for bulky external optical components.

Circularly polarized light, whose electric field rotates like a corkscrew as it travels, is essential for technologies such as 3D displays, advanced imaging systems, and quantum communication tools. Traditionally, generating this kind of light requires optical components such as polarizers and special plates that modify the light’s phase. However, these components make devices larger, more complex, and harder to integrate.

“Our goal is to simplify the way circularly polarized light is produced,” says corresponding author Shuhei Ichikawa. “By integrating polarization control directly into the LED with a specially designed metasurface, we remove the need for additional optical components.”

Experimental evidence shows how photons spread across multiple paths in an interferometer

The nature of quantum particles has long puzzled scientists. While single-particle interference suggests that a photon can behave like a spread-out wave, a whole photon is only ever detected in one specific place. Traditional interpretations of quantum mechanics often address this by suggesting the particle is in a superposition of being here and there at the same time. However, this tells us only where the particle is when it is measured, not where the particle physically is when no detector is present.

A research team led by Hiroshima University, led by Holger F. Hofmann, professor at the Graduate School of Advanced Science and Engineering, has now developed a method to measure this delocalization without disturbing the photon’s wave-like path.

In a study published in the New Journal of Physics, the researchers applied a modification of the well-established method of “weak measurements” to a two-path interferometer. As the photon traveled, they applied a tiny rotation by a positive angle in one path and a negative angle in the other. If the two paths interfere in the output, the average rotation angle is always zero. However, this is only a statistical average.

Quantum computer accurately simulates real magnetic materials, reproducing national laboratory data

Studying and designing novel materials is a central application of quantum mechanics. Chemists, materials scientists, and physicists focus on subtle interactions in quantum materials and to uncover them they rely on sophisticated computational and experimental techniques. Computer simulations that connect microscopic quantum interactions to measurable material properties complement experimental data to connect structure to function—but classical computers can struggle to simulate those properties. Fortunately, scientists today have a new tool in their toolbox: quantum computers.

In new preprint, a team of researchers from Oak Ridge National Lab’s (ORNL’s) Quantum Science Center (QSC), Purdue University, Los Alamos Laboratory, the University of Illinois at Urbana-Champaign, the University of Tennessee, and IBM used quantum simulation to compute the energy-momentum spectrum of a well-studied magnetic material, KCuF3, showing strong agreement with the spectra measured via neutron scattering. The research is published on the arXiv preprint server.

The quantum simulations employed the IBM Quantum Heron processor, while the experimental data was acquired from neutron sources at the Spallation Neutron Source (SNS) at ORNL and at the Rutherford Appleton Laboratory in the United Kingdom. This work serves as another realization of Richard Feynman’s vision: the use of a well-controlled, programmable quantum system to simulate the properties of a quantum system of interest.

Unlocking scalable entanglement will enable next-generation quantum computing

Quantum computing promises to transform our world in rapid, radical and revolutionary ways: solving in seconds problems that would take classical computers years, accelerating the discovery of new medicines, creating sustainable materials, optimizing complex systems, and strengthening cybersecurity. It does so using qubits, the quantum counterparts of classical bits, which can occupy multiple states simultaneously and enable a fundamentally new kind of computation.

For example, imagine 1,000 trucks need to arrive at 10,000 different locations, each, in different parts of the country. A traditional computation model would examine each of the 10 million possible routes one by one to evaluate their efficacy, but a quantum model would be able to evaluate all those millions of different routes instantaneously.

At the same time, quantum sensing is opening new frontiers in precision measurement, enabling technologies such as ultra-sensitive medical imaging and navigation systems that can detect minute changes in gravity or magnetic fields, capabilities that could allow doctors to identify diseases earlier or help vehicles navigate without GPS. UCF researchers believe the science of light, photonics, may hold the key to unlocking quantum computing’s true potential.

Building a National Quantum Strategy

Andrea Damascelli has always been fascinated by light. He uses it to probe materials on an atomic level, and his observations have contributed to the condensed-matter community’s understanding of high-temperature superconductors and quantum materials. His research group at the University of British Columbia (UBC) uses time-, spin-, and angle-resolved photoemission spectroscopy, an intricate technique that maps the energy and velocity of electrons as they propagate through materials.

In 2015, Damascelli spearheaded efforts that brought one of the first Canada First Research Excellence Fund (CFREF) grants to UBC’s Quantum Matter Institute. As the institute’s scientific director, he found himself at the helm of a full-blown research center—hiring faculty, expanding staff, and upgrading facilities. A few months later, he received a special request from Canada’s National Research Council: join leaders from across Canada’s quantum ecosystem to advise on a strategy for growing the country’s quantum community as a whole.

Physics Magazine chatted with Damascelli as he looked back on the beginning of Canada’s first National Quantum Strategy (NQS) and looked forward to developing a self-sustaining quantum research and training powerhouse.

DNA origami precisely positions single-photon emitters for quantum technologies

An international research team led by scientists from Skoltech has developed a method to position molecules on the surface of ultrathin materials with unprecedented precision using molecular DNA self-assembly, enabling the creation of quantum light sources. The results, published in the journal Light: Science & Applications, pave the way for the production of compact and efficient components for future quantum computers and secure communication networks.

Two-dimensional materials such as molybdenum disulfide are promising candidates for quantum light sources due to their ability to emit photons under laser excitation. However, until now, scientists have been unable to precisely control the location of emission centers—they emerged randomly upon ion beam irradiation or mechanical deformation of the material.

The authors of the study proposed a different approach. The research is based on the DNA origami method, which allows the construction of nanoscale objects of a specified shape from DNA molecules. Triangular structures measuring 127 nanometers were assembled, each carrying 18 thiol molecules. These structures were placed onto a silicon chip with a lithographic pattern. The positioning yield of each DNA origami structure at its designated location exceeded 90%, significantly surpassing the statistical limit of traditional single molecule deposition methods.

Making quantum vibrations nonlinear to enable phonon-phonon interactions

Phonons are the quantum units of mechanical vibration. They describe how motion propagates through a solid at the smallest possible scales, in much the same way that electrons describe electric currents. Because phonons can be exceptionally stable and sensitive, they are used in quantum science and technology.

Researchers can already detect and control individual phonons. The problem lies in making phonons interact with each other in a predictable and tunable way, which would be a key requirement for building complex quantum systems like quantum computers.

Interactions are essential in quantum technologies. Whether the goal is sensing tiny forces or processing information, one quantum excitation must be able to influence another. In practice, this requires nonlinearity, which means that adding one excitation changes how the system responds to the next, rather than each excitation behaving independently.

Now you see it, now you don’t: Material can transition between quantum states

A team of scientists led by the U.S. Department of Energy’s (DOE) Argonne National Laboratory has identified a rare, switchable quantum property in a new type of nickel sulfide material. The discovery could have applications in high-speed transistors, adaptive sensors and other devices that require a material’s electronic structure to be controlled on the fly. The research is published in the journal Matter.

The compound, KxNi4S2 (0 ≤ x ≤ 1), contains nickel and sulfur sandwiched between layers of potassium. The “(0 ≤ x ≤ 1)” in the name means that the amount of potassium in the material can vary from no potassium at all to a full potassium atom, depending on the sample.

First detailed in a 2021 paper, it was created as part of an ongoing quest to develop more superconductors. As researchers examined the layered material’s characteristics, they happened upon a remarkable feature: applying an electrical current could drive the potassium layers out, collapsing the sandwich and changing the material’s structure.

Dancing to invisible choreography, quantum computers can balance the noise

Large-scale quantum computers are waiting in the wings. One of the main reasons we don’t have them yet is because quantum hardware is so noisy. This isn’t the type of noise you’d want to shush in a crowded theater. When it comes to computers, noise means errors that crop up when conditions aren’t perfect.

“We need to find a way to detect errors and correct for them,” said graduate student Evangelos Piliouras. Working with physicist Ed Barnes, Piliouras devised a method to reduce the noise and make quantum computers more noise tolerant. His work was published in npj Quantum Information.

Noise can have real-world implications even in a traditional computer, which uses a stream of electrical signals called bits that represent the 1s and 0s that make up binary code. Noise can knock a 0 into a 1, and a credit card transaction, for instance, might fail.

/* */