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Category: quantum physics

A researcher from Skoltech has filled in the gaps connecting quantum simulators with more traditional quantum computers, discovering a new computationally universal model of quantum computation, the variational model. The paper was published as a Letter in the journal Physical Review A. The work made the Editors’ Suggestion list.

A is built to share properties with a target quantum system we wish to understand. Early quantum simulators were ‘dedicated’—that means they could not be programmed, tuned or adjusted and so could mimic one or very few target systems. Modern quantum simulators enable some control over their settings, offering more possibilities.

In contrast to quantum simulators, the long-promised quantum computer is a fully programmable quantum system. While building a fully programmable quantum remains elusive, noisy quantum processors that can execute short quantum programs and offer limited programmability are now available in leading laboratories around the world. These quantum processors are closer to the more established quantum simulators.

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A team of researchers and engineers at Canadian company Xanadu Quantum Technologies Inc., working with the National Institute of Standards and Technology in the U.S., has developed a programmable, scalable photonic quantum chip that can execute multiple algorithms. In their paper published in the journal Nature, the group describes how they made their chip, its characteristics and how it can be used. Ulrik Andersen with the Technical University of Denmark has published a News & Views piece in the same journal issue outlining current research on quantum computers and the work by the team in Canada.

Scientists around the world are working to build a truly useful quantum that can perform calculations that would take traditional computers millions of years to carry out. To date, most such efforts have been focused on two main architectures—those based on superconducting electrical circuits and those based on trapped-ion technology. Both have their advantages and disadvantages, and both must operate in a supercooled environment, making them difficult to scale up. Receiving less attention is work using a photonics-based approach to building a quantum computer. Such an approach has been seen as less feasible because of the problems inherent in generating quantum states and also of transforming such states on demand. One big advantage photonics-based systems would have over the other two architectures is that they would not have to be chilled—they could work at room temperature.

In this new effort, the group at Xanadu has overcome some of the problems associated with photonics-based systems and created a working programmable photonic quantum chip that can execute multiple algorithms and can also be scaled up. They have named it the X8 photonic quantum processing unit. During operation, the is connected to what the team at Xanadu describe as a “squeezed light” source—infrared laser pulses working with microscopic resonators. This is because the new system performs continuous variable quantum computing rather than using single-photon generators.

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Foresight Molecular Machines Group.
Program & apply to join: https://foresight.org/molecular-machines/

Joe Lyding.
Silicon-Based Nanotechnology: There’s Still Plenty of Room at the Bottom.
Joe Lyding is a distinguished professor in Electrical and Computer Engineering at the University of Illinios. His career includes constructing the first atomic resolution scanning tunneling microscope, discovering new industrial uses for deuterium, studying quantum size effects down to 2nm lateral graphene dimensions, and much more. His current research is focused on carbon nanoelectronics. Specifically using carbon nanoelectronics based on carbon nanotubes and graphene for future semiconducting device applications.

Leonhard Grill.
Every Atom Counts: Manipulating Single Molecules on Surfaces.
Leonhard Grill is a professor at the University of Graz, where he leads a research group on nanoscience. His research focuses on imaging, characterization and manipulation of single functional molecules adsorbed on surfaces by using scanning tunneling microscopy, typically at cryogenic temperatures and under ultrahigh vacuum conditions.

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We argue in a model-independent way that the Hilbert space of quantum gravity is locally finite-dimensional. In other words, the density operator describing the state corresponding to a small region of space, when such a notion makes sense, is defined on a finite-dimensional factor of a larger Hilbert space. Because quantum gravity potentially describes superpo-sitions of different geometries, it is crucial that we associate Hilbert-space factors with spatial regions only on individual decohered branches of the universal wave function. We discuss some implications of this claim, including the fact that quantum field theory cannot be a fundamental description of Nature.

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Quanta of light—photons—form the basis of quantum key distribution in modern cryptographic networks. Before the huge potential of quantum technology is fully realized, however, several challenges remain. A solution to one of these has now been found.

In a paper published in the journal Science, teams led by David Novoa, Nicolas Joly and Philip Russell report a breakthrough in frequency up-conversion of single photons, based on a hollow-core photonic crystal fiber (PCF) filled with hydrogen gas. First a spatio-temporal hologram of molecular vibrations is created in the gas by stimulated Raman scattering. This hologram is then used for highly efficient, correlation-preserving frequency conversion of single photons. The system operates at a pressure-tuneable wavelength, making it potentially interesting for quantum communications, where efficient sources of indistinguishable single-photons are unavailable at wavelengths compatible with existing fiber networks.

The approach combines , gas-based , hollow-core PCF, and the physics of molecular vibrations to form an efficient tool that can operate in any spectral band from the ultraviolet to the mid-infrared—an ultra-broad working range inaccessible to existing technologies. The findings may be used to develop fiber-based tools in technologies such as , and quantum-enhanced imaging.

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Physicists from Paderborn University have developed a novel concept for generating individual photons—tiny particles of light that make up electromagnetic radiation—with tailored properties, the controlled manipulation of which is of fundamental importance for photonic quantum technologies. The findings have now been published in the journal Nature Communications.

Professor Artur Zrenner, head of the “nanostructure optoelectronics” research group, explains how tailored desired states have so far posed a challenge: “Corresponding sources are usually based on light emissions from individual semiconductor quantum emitters, which generate the photons. Here, the properties of the emitted photons are defined by the fixed properties of the quantum emitter, and can therefore not be controlled with full flexibility.”

To get around the problem, the scientists have developed an all-optical, non-linear method to tailor and control single photon emissions. Based on this concept, they demonstrate laser-guided energy tuning and polarization control of photons (i.e., the light frequency and direction of oscillation of electromagnetic waves).

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Future quantum computers are expected not only to solve particularly tricky computing tasks, but also to be connected to a network for the secure exchange of data. In principle, quantum gates could be used for these purposes. But until now, it has not been possible to realize them with sufficient efficiency. By a sophisticated combination of several techniques, researchers at the Max Planck Institute of Quantum Optics (MPQ) have now taken a major step towards overcoming this hurdle.

For decades, computers have been getting faster and more powerful with each . This development makes it possible to constantly open up new applications, for example in systems with artificial intelligence. But further progress is becoming increasingly difficult to achieve with established computer technology. For this reason, researchers are now setting their sights on alternative, completely new concepts that could be used in the future for some particularly difficult computing tasks. These concepts include quantum computers.

Their function is not based on the combination of digital zeros and ones—the classical bits—as is the case with conventional, microelectronic computers. Instead, a quantum computer uses , or qubits for short, as the basic units for encoding and processing information. They are the counterparts of bits in the quantum world—but differ from them in one crucial feature: qubits can not only assume two fixed values or states such as zero or one, but also any values in between. In principle, this offers the possibility to carry out many computing processes simultaneously instead of processing one logical operation after the other.

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The digital device you are using to view this article is no doubt using the bit, which can either be 0 or 1, as its basic unit of information. However, scientists around the world are racing to develop a new kind of computer based on the use of quantum bits, or qubits, which can simultaneously be 0 and 1 and could one day solve complex problems beyond any classical supercomputers.

A research team led by scientists at the U.S. Department of Energy’s (DOE) Argonne National Laboratory, in close collaboration with FAMU-FSU College of Engineering Associate Professor of Mechanical Engineering Wei Guo, has announced the creation of a new qubit platform that shows great promise to be developed into future quantum computers. Their work is published in the journal Nature.

“Quantum computers could be a revolutionary tool for performing calculations that are practically impossible for classical computers, but there is still work to do to make them reality,” said Guo, a paper co-author. “With this research, we think we have a breakthrough that goes a long way toward making qubits that help realize this technology’s potential.”

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Over the years, supercomputers have played a pivotal role in pushing the frontiers of science. Earlier this year, Meta launched one of the fastest AI supercomputers, the AI Research SuperCluster (RSC), to build sophisticated AI models that can learn from trillions of examples; navigate hundreds of different languages; seamlessly analyse text, images, and video together; build AR tools etc.

However, the quest for something even faster than supercomputers led to the development of quantum computers. Last year, the University of Science and Technology of China (USTC) introduced the world’s fastest programmable superconducting quantum computer; Zuchongzhi 2.1 is a million times faster than a conventional computer.

At last year’s I/O conference, Google unveiled a Quantum AI campus in Santa Barbara, California, complete with a quantum data centre, quantum hardware research labs, and quantum processor chip fab facilities. The tech giant plans to build a useful, error-corrected quantum computer within a decade.

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