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Category: quantum physics – Page 21

Quantum-Secure Ballots Demonstrated in the Lab

Quantum bits (qubits) enable these conditions. The quantum voting protocol involves creating a quantum state of many quantum-entangled qubits known as a Greenberger-Horne-Zeilinger (GHZ) state, with one qubit for each voter. The state can be prepared so that each qubit measurement randomly produces 0 or 1, but the entanglement guarantees that the total number of 1s is either even or odd. These states can be prepared using, for example, photons as qubits, with 0 and 1 corresponding to distinct polarization states.

Such a protocol was proposed in 2022 by quantum information theorist Federico Centrone of the Barcelona Institute of Science and Technology in Spain and his co-workers [3]. Implementing it requires that the voters be able to verify that they have been given a true GHZ state and not some other state that subverts the protocol. Such verifications can be carried out, but each qubit can only be used once—either for voting or for verification. So extra sets of GHZ states must be produced for multiple rounds of verification.

Two research teams have now demonstrated the fundamental features of the protocol using photons as qubits, although several practical challenges remain before it can be used in a real election. Joey Marcellino, a PhD student at the University of Geneva, and his co-workers randomly assign each round as either a verification or a voting round [1]. Meanwhile, Laurent-Puig and his colleagues (including Centrone) simply chose to postpone the verification aspect of the protocol for future work [2].

Physicists watch a material’s electrons assemble, and reassemble, into coexisting phases

A tall glass of ice water isn’t just a thirst quencher; it’s also an everyday example of coexisting phases. Water can exist simultaneously in both liquid and solid phases. As it turns out, this phase duality can also exist in more exotic quantum materials, in ways that are far more complicated to tease apart.

A new study by MIT physicists sheds light on how two different phases of electron behavior can emerge and coexist in the same quantum material.

Their results, reported in the journal Nature Physics, can help explain how some materials host superconductivity, magnetism and other electronic phases. Untangling such phases and understanding how they emerge will help engineers control electronic behavior and design high-performance quantum devices.

Crossing into a mirror world: Particles turn to wisps of fog, and the magnetic monopole paradox dissolves

In Goethe’s ballad “Erlkönig,” immortalized in Schubert’s fevered 1815 setting, a dying boy riding through the night sees a spectral king beckoning from the darkness. His father calms him: “Mein Sohn, es ist ein Nebelstreif”—my son, it is only a wisp of fog. In the poem, the father’s reassurance proves tragically wrong. In the quantum world, however, his words acquire an uncanny new meaning.

For four decades, physicists have been haunted by their own apparition: a particle that scatters off a magnetic monopole and seems to vanish from the theory entirely, its outgoing state missing from the books. A team of physicists from Ghent University, the University of Cambridge and the University of Oxford now shows, in a paper published in Nature Physics, where such particles go.

Throwing quantum wave packets at a so-called “duality defect”—an interface stitching together two quantum worlds that are secretly descriptions of the same physics—they find that the particle is never reflected: it always passes through, with 100% probability, and reemerges as precisely what the father promised. A wisp of fog: faint, smeared out, trailing an invisible thread of quantum mist back to the mirror’s edge.

New ‘shape-shifting’ architecture brings versatility to photonic quantum computing

Using light to process quantum information is one of the most promising approaches to building future quantum computers. Light particles, known as photons, are excellent carriers of quantum information, but their lack of natural interactions has created a major challenge for researchers seeking to build systems capable of performing a full range of computations.

Now, researchers from Imperial’s Department of Physics and external collaborators have developed a new architecture, called Clavina, that overcomes this longstanding limitation.

Published in Nature Photonics, the study demonstrates a programmable platform that combines both linear and nonlinear quantum operations within a single system, expanding the capabilities of quantum computers that use light.

Physics In History (@PhysInHistory) on X

The Longest Equation in Physics The model Lagrangian is a mathematical expression that summarizes the Standard Model of particle physics, which is the most successful theory of the fundamental interactions between elementary particles. It is composed of four different parts, each describing a different aspect of the Standard Model. The model Lagrangian is written in a compact notation that uses symbols and operators from quantum field theory, such as covariant derivatives, field strength tensors, Dirac matrices, and gauge group generators. It also uses various constants and parameters that are determined by experiments, such as coupling constants, masses, and mixing angles. It is one of the longest equations in physics because it contains many terms and factors that account for all the possible interactions and symmetries of the Standard Model. It was transcribed by Thomas Gutierrez who derived it from Martinus Veltman’s Diagrammatica: The Path to Feynman Diagrams.

Repurposing deep-Earth tools in the hunt for practical superconductors

If scientists could find a material that acts as a superconductor—that is, one that transmits energy with zero resistance—at normal pressures and relatively high temperatures, it would open up a vast number of possibilities. These include medical imaging, quantum computing and numerous other fields. So, yes, it would be a big deal.

“Right now, almost 50% of the energy in transmission is just heat in copper wires,” said Shomeek Mukhopadhyay. “If you can transmit electricity through wires without dissipating energy, that’s a huge economic benefit. I would say it’s equivalent to having thermonuclear fusion.”

Mukhopadhyay, a research scientist in Chemical & Environmental Engineering, is on the third floor of the Kline Geology Laboratory. Nearby, Natalia Nevskaya, a postdoctoral associate in Earth & Planetary Sciences, prepares a massive device called the Kawai multi-anvil press.

Sunlight-powered setup generates quantum entanglement

Today’s quantum technologies rely on energy-intensive lasers, raising concerns that scaling them up could further increase energy demands. In new work, researchers have demonstrated that quantum entanglement between photons can be generated directly from sunlight, offering a potential alternative.

“Quantum entanglement is crucial for applications such as secure communication, ultra-precise sensing and high-performance computation,” said Cheng Li, a recent graduate of the University of Ottawa in Canada. “Our work shows that abundant natural light sources can be used for quantum entanglement, opening the possibility of more energy-efficient and accessible quantum technologies.”

In Optica, the researchers report that the entanglement they achieved using sunlight was comparable to laser-based approaches after accounting for differences in the bandwidth of the input light.

Two-qubit entangling gate flags its own errors as detectable photon losses

Quantum errors are a normal part of quantum computing because fragile physical qubits (the tiny components storing data) can easily break down because of environmental noise, like heat, stray signals or microscopic vibrations. Typical fixes involve vast amounts of extra hardware qubits, which make computers larger, more expensive and harder to build.

In a paper published in the journal Nature, scientists report developing a two-qubit entangling gate that automatically flags its most common errors as they occur.

The team at D-Wave Quantum Inc. engineered an ultrafast link, called a controlled-Z (CZ) entangling gate, that entangles two qubits in just 500 nanoseconds. When errors occur, the system automatically flags most of them as photon losses (known as erasures) instead of letting them turn into hidden glitches.

X(2370) emerges as glueball-dominated particle in collider experiments

At the International Conference on High Energy Physics in Brazil, the BESIII Collaboration report that, after 15 years of sustained research, it identified the dominant constituent of the X(2370) as a pseudoscalar glueball with spin-parity quantum numbers of 0⁻⁺

The strong interaction force tightly binds quarks inside protons and neutrons. Its mediator is called the gluon, just as the photon mediates the electromagnetic interaction. Notably, however, gluons can attract each other and form an entirely new particle—a bound state called a glueball.

The glueball is an important prediction of quantum chromodynamics, the theory that describes the strong interaction, and is also the only type of particle in nature composed entirely of force mediators. No particle of this kind has ever been observed experimentally, and its existence constitutes a crucial test of quantum chromodynamics.

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