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A group of researchers led by Andreas Wallraff, Professor of Solid State Physics at ETH Zurich, has performed a loophole-free Bell test to disprove the concept of “local causality” formulated by Albert Einstein in response to quantum mechanics.

By showing that quantum mechanical objects that are far apart can be much more strongly correlated with each other than is possible in conventional systems, the researchers have provided further confirmation for quantum mechanics. What’s special about this experiment is that the researchers were able for the first time to perform it using superconducting circuits, which are considered to be promising candidates for building powerful quantum computers.

A Bell test is based on an experimental setup that was initially devised as a thought experiment by British physicist John Bell in the 1960s. Bell wanted to settle a question that the greats of physics had already argued about in the 1930s: Are the predictions of quantum mechanics, which run completely counter to everyday intuition, correct, or do the conventional concepts of causality also apply in the atomic microcosm, as Albert Einstein believed?

In a result decades in the making, Los Alamos scientists have achieved light amplification with electrically driven devices based on solution-cast semiconductor nanocrystals—tiny specs of semiconductor matter made via chemical synthesis and often called colloidal quantum dots.

This demonstration, reported in the journal Nature, opens the door to a completely new class of electrically pumped lasing devices—highly flexible, solution-processable laser diodes that can be prepared on any crystalline or non-crystalline substrate without the need for sophisticated vacuum-based growth techniques or a highly controlled clean-room environment.

“The capabilities to attain light amplification with electrically driven colloidal quantum dots have emerged from decades of our previous research into syntheses of nanocrystals, their photophysical properties and optical and electrical design of quantum dot devices,” said Victor Klimov, Laboratory Fellow and leader of the quantum dot research initiative.

Quantum dots in semiconductors such as silicon or gallium arsenide have long been considered hot candidates for hosting quantum bits in future quantum processors. Scientists at Forschungszentrum Jülich and RWTH Aachen University have now shown that bilayer graphene has even more to offer here than other materials.

The double quantum dots they have created are characterized by a nearly perfect electron-hole-symmetry that allows a robust read-out mechanism—one of the necessary criteria for quantum computing. The results were published in Nature.

The development of robust semiconductor spin qubits could help the realization of large-scale quantum computers in the future. However, current quantum dot based qubit systems are still in their infancy. In 2022, researchers at QuTech in the Netherlands were able to create 6 silicon-based spin qubits for the first time. With graphene, there is still a long way to go. The material, which was first isolated in 2004, is highly attractive to many scientists. But the realization of the first quantum bit has yet to come.

In two landmark experiments, researchers used quantum processors to engineer exotic particles that have captivated physicists for decades. The work is a step toward crash-proof quantum computers.

It is often desirable to restrict flows—whether of sound, electricity, or heat—to one direction, but naturally occurring systems almost never allow this. However, unidirectional flow can indeed be engineered under certain conditions, and the resulting systems are said to exhibit chiral behavior.

The concept of chirality is traditionally limited to single direction flows in one dimension. In 2021, however, researchers working with Taylor Hughes, a professor of physics at the University of Illinois Urbana-Champaign, introduced a theoretical extension that can account for more intricate chiral flows in two dimensions.

Now, a team led by Hughes and Gaurav Bahl, a UIUC professor of mechanical science & engineering, has experimentally realized this extension. As the researchers reported in Nature Communications, they constructed a topological circuit network, a system of electronics that simulates the microscopic behavior of quantum materials, to explore the entirely new behaviors predicted by this extended, or higher-rank chirality.

The 2022 physics Nobel prize was awarded for experimental work demonstrating fundamental breaks in our understanding of the quantum world, leading to discussions around “local realism” and how it could be refuted. Many theorists believe these experiments challenge either “locality” (the notion that distant objects require a physical mediator to interact) or “realism” (the idea that there’s an objective state of reality). However, a growing number of experts suggest an alternative approach, “retrocausality,” which posits that present actions can affect past events, thus preserving both locality and realism.

The 2022 Nobel Prize in physics highlighted the challenges quantum experiments pose to “local realism.” However, a growing body of experts propose “retrocausality” as a solution, suggesting that present actions can influence past events, thus preserving both locality and realism. This concept offers a novel approach to understanding causation and correlations in quantum mechanics, and despite some critics and confusion with “superdeterminism,” it is increasingly seen as a viable explanation for recent groundbreaking experiments, potentially safeguarding the core principles of special relativity.

In 2022, the physics Nobel prize was awarded for experimental work showing that the quantum world must break some of our fundamental intuitions about how the universe works.

A time crystal, as originally proposed in 2012, is a new state of matter in which the particles are in continuous oscillatory motion. Time crystals break time-translation symmetry. Discrete time crystals do so by oscillating under the influence of a periodic external parametric force, and this type of time crystal has been demonstrated in trapped ions, atoms and spin systems.

Continuous time crystals are more interesting and arguably more important, as they exhibit continuous time-translation symmetry but can spontaneously enter a regime of periodic motion, induced by a vanishingly small perturbation. It is now understood that this state is only possible in an open system, and a continuous quantum-time-crystal state has recently been observed in a quantum system of ultracold atoms inside an optical cavity illuminated with light.

In a paper published in Nature Physics, researchers at University of Southampton in the U.K. showed that a classical metamaterial nanostructure can be driven to a state that exhibits the same key characteristics of a continuous time crystal.

According to the rules of thermodynamics, you need infinite time or energy to achieve absolute zero. But a new study says there is another way.

Light, sound, and heat are all types of energy around us. Thermodynamics is a branch of science that helps us understand how energy moves between objects. According to the third law of thermodynamics, it is impossible to cool any object to-273.15 degrees C (or absolute zero), which is the lowest temperature possible.

Now a research team from the Vienna University of Technology in Austria has found a way to cool an object to absolute zero. The study published in PRX Quantum demonstrates this alternate route using quantum computing.

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The motion of an electron in a strong infrared laser field is tracked in real time by means of a novel method developed by MPIK physicists and applied to confirm quantum-dynamics theory by cooperating researchers at MPI-PKS. The experimental approach links the absorption spectrum of the ionizing extreme ultraviolet pulse to the free-electron motion driven by the subsequent near-infrared pulse. Their paper is published in the journal Physical Review Letters.

For this experimental scheme, the classical description of the electron motion is justified even though it is a quantum object. In the future, the new method demonstrated here for helium can be applied to more complex systems such as larger atoms or molecules for a broad range of intensities.

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