Controlling qubits with quantum superpositions allows them to dramatically violate a fundamental limit and encode information for about five times longer during quantum computations
Category: quantum physics
Caltech Team Sets Record with 6,100-Qubit Array
Quantum computers will need large numbers of qubits to tackle challenging problems in physics, chemistry, and beyond. Unlike classical bits, qubits can exist in two states at once—a phenomenon called superposition. This quirk of quantum physics gives quantum computers the potential to perform certain complex calculations better than their classical counterparts, but it also means the qubits are fragile. To compensate, researchers are building quantum computers with extra, redundant qubits to correct any errors. That is why robust quantum computers will require hundreds of thousands of qubits.
Now, in a step toward this vision, Caltech physicists have created the largest qubit array ever assembled: 6,100 neutral-atom qubits trapped in a grid by lasers. Previous arrays of this kind contained only hundreds of qubits.
This milestone comes amid a rapidly growing race to scale up quantum computers. There are several approaches in development, including those based on superconducting circuits, trapped ions, and neutral atoms, as used in the new study.
The neutral-atom platform shows promise for scaling up quantum computers.
How Bose-Einstein condensates replicate Shapiro steps
The microscopic processes taking place in superconductors are difficult to observe directly. Researchers at the RPTU University of Kaiserslautern-Landau have therefore implemented a quantum simulation of the Josephson effect: They separated two Bose-Einstein condensates (BECs) by means of an extremely thin optical barrier.
The characteristic Shapiro steps were observed in the atomic system. The research was published in the journal Science.
Two superconductors separated by a wafer-thin insulating layer—that’s how simple a Josephson junction looks. But despite its simple structure, it harbors a quantum mechanical effect that is now one of the most important tools of modern technology: Josephson contacts form the heart of many quantum computers and enable high-precision measurements—such as the measurement of very weak magnetic fields.
Pinpointing the glow of a single atom to advance quantum emitter engineering
Researchers have discovered how to design and place single-photon sources at the atomic scale inside ultrathin 2D materials, lighting the path for future quantum innovations.
Like perfectly controlled light switches, quantum emitters can turn on the flow of single particles of light, called photons, one at a time. These tiny switches—the “bits” of many quantum technologies—are created by atomic-scale defects in materials.
Their ability to produce light with such precision makes them essential for the future of quantum technologies, including quantum computing, secure communication and ultraprecise sensing. But finding and controlling these atomic light switches has been a major scientific challenge—until now.
String Theory Inspires a Brilliant, Baffling New Math Proof
When the team posted their proof in August, many mathematicians were excited. It was the biggest advance in the classification project in decades, and hinted at a new way to tackle the classification of polynomial equations well beyond four-folds.
But other mathematicians weren’t so sure. Six years had passed since the lecture in Moscow. Had Kontsevich finally made good on his promise, or were there still details to fill in?
And how could they assuage their doubts, when the proof’s techniques were so completely foreign — the stuff of string theory, not polynomial classification? “They say, ‘This is black magic, what is this machinery?’” Kontsevich said.
Time might not exist — and we’re starting to understand why
Consider two events, A and B, such as flashes of light made by two sources in different places.
Cause and effect means there are three possibilities: 1) Flash A happened before flash B, and via some mechanism, could have triggered B; 2) Flash B happened before Flash A and could have triggered it; 3) Neither one could have triggered the other because they are too far apart in space and too close in time for a triggering signal to have been sent from one location to the other.
Now, Einstein’s Special Theory of Relativity states that all observers, no matter how fast they’re moving relative to each other, see light travelling at the same constant speed.
This strange but simple fact can lead to observers seeing events happening in different orders.
For option above, two observers moving relative to each other close to the speed of light might disagree on the ordering of flashes.
Thankfully, there’s no danger of an effect coming before its cause (known as a ‘violation of causality’) since the events are too far apart for either to cause the other.
However, what if options and coexisted in a quantum superposition? The causal order of the two events would no longer be fixed.
From fullerenes to 2D structures: A unified design principle for boron nanostructures
Boron, a chemical element next to carbon in the periodic table, is known for its unique ability to form complex bond networks. Unlike carbon, which typically bonds with two or three neighboring atoms, boron can share electrons among several atoms. This leads to a wide variety of nanostructures. These include boron fullerenes, which are hollow, cage-like molecules, and borophenes, ultra-thin metallic sheets of boron atoms arranged in triangular and hexagonal patterns.
Dr. Nevill Gonzalez Szwacki has developed a model explaining the variety of boron nanostructures. The analysis, published in the journal 2D Materials, combines more than a dozen known boron nanostructures, including the experimentally observed B₄₀ and B₈₀ fullerenes.
Using first-principles quantum-mechanical calculations, the study shows that the structural, energetic, and electronic properties of these systems can be predicted by looking at the proportions of atoms with four, five, or six bonds. The results reveal clear links between finite and extended boron structures. The B₄₀ cage corresponds to the χ₃ borophene layer, while B₆₅, B₈₀, and B₉₂ connect with the β₁₂, α, and bt borophene sheets, respectively. These structural links suggest that new boron cages could be created by using known two-dimensional boron templates.
Growth strategy enables coherent quantum transport in single-layer MoS₂ semiconductors
Two-dimensional (2D) semiconductors are thin materials (i.e., one-atom thick) with advantageous electronic properties. These materials have proved to be promising for the development of thinner, highly performing electronics, such as fitness trackers and portable devices.
A 2D semiconductor that has attracted particular interest within the electronics community is molybdenum disulfide (MoS₂), a transition-metal dichalcogenide made up of one metal atom and two chalcogen atoms. To build reliable large-area electronics based on MoS₂ layers, engineers need to uniformly grow this material over wafer-scale surfaces, minimizing defects that hinder the performance of devices.
Researchers at the Institute for Basic Science (IBS), Pohang University of Science and Technology (POSTECH) and other institutes recently introduced a new approach to grow single-layer MoS₂ on substrates while maintaining a uniform atomic arrangement. Their approach, outlined in a paper in Nature Electronics, entails a greater control of the process by which small crystal regions merge on a substrate, also known as coalescence.
Real-life ‘quantum molycircuits’ using exotic nanotubes
Molybdenum disulfide MoS2 is a groundbreaking material for electronics applications. As a two-dimensional layer similar to graphene, it is an excellent semiconductor, and can even become intrinsically superconducting under the right conditions. It’s not particularly surprising that science fiction authors have already been speculating about molycircs, fictional computer circuits built from MoS2, for years—and that physicists and engineers are directing huge research efforts at this material.
Researchers at the University of Regensburg, have many years of expertise with diverse quantum materials—in particular also with carbon nanotubes, tube-like macromolecules made from carbon atoms alone.
“It was an obvious next step to now focus on MoS2 and its fascinating properties,” said Dr. Andreas K. Hüttel, head of the research group Nanotube Electronics and Nanomechanics in Regensburg. In cooperation with Prof. Dr. Maja Remškar, Jožef Stefan Institut Ljubljana, a specialist in the crystalline growth of molybdenum disulfide nanomaterials, his research group started working on quantum devices based on MoS2 nanotubes.