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A heptagonal-lattice superconducting circuit, and the mathematics that describe it, provide tools for studying quantum mechanics in curved space.

According to John Wheeler’s summary of general relativity, “space-time tells matter how to move; matter tells space-time how to curve.” How this relationship plays out at the quantum scale is not known, because extending quantum experiments to curved space poses a challenge. In 2019, Alicia Kollár and colleagues at Princeton University met that challenge with a photonic circuit that represents the negatively curved space of an expanding universe [1]. Now, Igor Boettcher and colleagues at the University of Maryland, College Park, describe those experiments with a new theoretical framework [2]. Together, the studies offer a toolkit for studying quantum mechanics in curved space that could help answer fundamental questions about cosmology.

In a universe that expands at an accelerating rate, space curves away from itself at every point, producing a saddle-like, hyperbolic geometry. To project hyperbolic space onto a plane, Kollár’s team etched a centimeter-sized chip with superconducting resonators arranged in a lattice of heptagonal tiles. By decreasing the tile size toward the edge of the chip, the researchers reproduced a perplexing property of hyperbolic space: most of its points exist on its boundary. As a result, photons moving through the circuit behave like particles moving in negatively curved space.

Natalia Herrera-Valencia and colleagues have successfully unscrambled entangled light after it has passed through a 2 m long multimode fibre. Led by Mehul Malik, the team at the Heriot-Watt University in Edinburgh tackled the challenge using entanglement itself. The research was done in collaboration with a colleague at the University of Glasgow and is described in a recent paper in Nature Physics.

Light passing through a disordered (or “complex”) medium like atmospheric fog or a multimode fibre gets scattered, albeit in a known manner. As a result, the information carried by the light gets distorted but is preserved, and extra steps are needed to access it. This gets especially tricky for the transport of entangled states of light because the medium muddles up the quantum correlations. The states get “scrambled” and “unscrambling” becomes necessary to retrieve the original entangled states.

First photonic quantum computer on the cloud.

Even quantum computers make mistakes. Their computing ability is extraordinary, exceeding that of classical computers by far. This is because circuits in quantum computers are based on qubits that can represent not only zeroes or ones, but also superpositions of both states by using the principles of quantum mechanics. Despite their great potential, qubits are extremely fragile and prone to errors due to the interactions with the external environment.

To solve this crucial issue, an international research group developed and implemented a new protocol that protects fragile quantum information and corrects errors due to qubit loss. This research group published the results of their study in Nature.

“Developing a fully functioning quantum processor still represents a great challenge for scientists across the world,” explains Davide Vodola who is one of the authors of the study as well as a researcher at the University of Bologna. “This research allowed us, for the first time, to implement a protocol that can detect and, at the same time, correct errors due to qubit loss. This ability could prove to be essential for the future development of large-scale quantum computers.”

Circa 2015. What if a hull of ship could have warp crystals that could slip through space time easier.

Crystals, as quantum objects typically much larger than their lattice spacing, are a counterexample to a frequent prejudice that quantum effects should not be pronounced at macroscopic distances. We propose that the Einstein theory of gravity only describes a fluid phase and that a phase transition of crystallization can occur under extreme conditions such as those inside the black hole. Such a crystal phase with lattice spacing of the order of the Planck length offers a natural mechanism for pronounced quantum-gravity effects at distances much larger than the Planck length. A resolution of the black-hole information paradox is proposed, according to which all information is stored in a crystal-phase remnant with size and mass much above the Planck scale.

Future wireless networks of the 6th generation (6G) will consist of a multitude of small radio cells that need to be connected by broadband communication links. In this context, wireless transmission at THz frequencies represents a particularly attractive and flexible solution. Researchers at Karlsruhe Institute of Technology (KIT) have now developed a novel concept for low-cost terahertz receivers that consist of a single diode in combination with a dedicated signal processing technique. In a proof-of-concept experiment, the team demonstrated transmission at a data rate of 115 Gbit/s and a carrier frequency of 0.3 THz over a distance of 110 meters. The results are reported in Nature Photonics.

5G will be followed by 6G: The sixth generation of mobile communications promises even higher data rates, shorter latency, and strongly increased densities of terminal devices, while exploiting Artificial Intelligence (AI) to control devices or autonomous vehicles in the Internet-of-Things era. “To simultaneously serve as many users as possible and to transmit data at utmost speed, future wireless networks will consist of a large number of small radio cells,” explains Professor Christian Koos, who works on 6G technologies at KIT together with his colleague Professor Sebastian Randel. In these radio cells, distances are short such that high data rates can be transmitted with minimum energy consumption and low electromagnetic immission. The associated base stations will be compact and can easily be mounted to building facades or street lights.

To form a powerful and flexible network, these base stations need to be connected by high-speed wireless links that offer data rates of tens or even hundreds of gigabits per second (Gbit/s). This may be accomplished by terahertz carrier waves, which occupy the frequency range between microwaves and infrared light waves. However, terahertz receivers are still rather complex and expensive and often represent the bandwidht bottleneck of the entire link. In cooperation with Virginia Diodes (VDI) in Charlottesville, U.S., researchers of KIT’s Institute of Photonics and Quantum Electronics (IPQ), Institute of Microstructure Technology (IMT), and Institute for Beam Physics and Technology (IBPT) have now demonstrated a particularly simple inexpensive receiver for terahertz signals. The concept is presented in Nature Photonics.

Emerging quantum materials can be defined by topology and strong electron correlations, although their applications in experimental systems are relatively limited. Weyl semimetals incorporating magnetism offer a unique and fertile platform to explore emerging phenomena in developing topological matter and topological spintronics. The triangular antiferromagnet Mn₃Sn exhibits many exotic physical properties as an antiferromagnetic (AFM) Weyl semimetal (WSM), including an attractively large spontaneous Hall effect.

The spontaneous Hall effect was discovered more than a century ago and understood in terms of time-reversal symmetry breaking by the internal spin structure of antiferromagnetic, ferromagnetic or skyrmionic (small swirling topological defects in the magnetization) forms.

In a new report now published on Science Advances, Durga Khadka and a team of scientists in physics, materials science, neutron research and engineering in the U.S. reported the synthesis of epitaxial Mn_3+x Sn_1−x films with compositions similar to bulk samples. When they replaced the tin (Sn) atoms with magnetic manganese (Mn) atoms in the samples, they noted the Kondo effect; a celebrated example of strong correlations to emerge, then develop coherence and induce a hybridization energy gap. The process of magnetic doping and gap opening facilitated rich extraordinary properties for the new materials.

To maintain its leadership in quantum computing technology, the US must embrace a culture shift that fuses three important elements: science, a roadmap, and agility.

The achievement opens a pathway for development of the first practical and efficient devices to generate and detect light at terahertz wavelengths—between infrared light and microwaves. Such devices could be used in applications as diverse as communications in outer space, cancer detection, and scanning for concealed weapons.

The research could also enable exploration of the basic physics of matter at infinitesimally small scales and help usher in an era of quantum metamaterials, whose structures are engineered at atomic dimensions.