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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 have now developed a novel concept for low-cost terahertz receivers. More
Inspired by the need for new and better therapies for neurodegenerative diseases, researchers are exploring the link between uncontrolled inflammation within the brain and the brain’s immune cells, known as microglia, which are emerging as a promising cellular target because of the prominent role they play in brain inflammation. The group highlights the design considerations and benefits of creating therapeutic nanoparticles for carrying pharmacological factors directly to the sites of the microglia. More
A recent study has shed new light on the Minoan system of fractions, one of the outstanding enigmas tied to the ancient writing of numbers. More
In physics, it is essential to be able to show a theoretical assumption in actual, physical experiments. For more than a hundred years, physicists have been aware of the link between the concepts of disorder in a system, and information obtained by measurement. However, a clean experimental assessment of this link in common monitored systems, that is systems which are continuously measured over time, was missing so far. More
Structural coloration is promised to be the display technology of the future as there is no fading – it does not use dyes – and enables low-power displays without strong external light source. However, the disadvantage of this technique is that once a device is made, it is impossible to change its properties so the reproducible colors remain fixed. Recently, a research team has successfully obtained vivid colors by using semiconductor chips – not dyes – made by mimicking the human brain structure. More
A fifth of carbon dioxide emissions come from multinational companies’ global supply chains, according to a new study that shows the scope of multinationals’ influence on climate change. More
Quantum bits, or qubits, can hold quantum information much longer now thanks to efforts by an international research team. The researchers have increased the retention time, or coherence time, to 10 milliseconds — 10,000 times longer than the previous record — by combining the orbital motion and spinning inside an atom. Such a boost in information retention has major implications for information technology developments since the longer coherence time makes spin-orbit qubits the ideal candidate for building large quantum computers.
They published their results on July 20 in Nature Materials.
“We defined a spin-orbit qubit using a charged particle, which appears as a hole, trapped by an impurity atom in silicon crystal,” said lead author Dr. Takashi Kobayashi, research scientist at the University of New South Wales Sydney and assistant professor at Tohoku University. “Orbital motion and spinning of the hole are strongly coupled and locked together. This is reminiscent of a pair of meshing gears where circular motion and spinning are locked together.”
Qubits have been encoded with spin or orbital motion of a charged particle, producing different advantages that are highly demanded for building quantum computers. To utilize the advantages of qubits, Kobayashi and the team specifically used an exotic charged particle “hole” in silicon to define a qubit, since orbital motion and spin of holes in silicon are coupled together.
Spin-orbit qubits encoded by holes are particularly sensitive to electric fields, according to Kobayashi, which allows for more rapid control and benefits scaling up quantum computers. However, the qubits are affected by electrical noise, limiting their coherence time.
“In this work, we have engineered sensitivity to the electric field of our spin-orbit qubit by stretching the silicon crystal like a rubber band,” Kobayashi said. “This mechanical engineering of the spin-orbit qubit enables us to remarkably extend its coherence time, while still retaining moderate electrical sensitivity to control the spin-orbit qubit.”
Think of gears in a watch. Their individual spinning propels the entire mechanism to keep time. It is neither the spin nor orbital motion, but a combination of them that takes the information forward.
“These results open a pathway to develop new artificial quantum systems and to improve the functionality and scalability of spin-based quantum technologies,” Kobayashi said.
This work was supported in part by the ARC Centre of Excellence for Quantum Computation and Communication Technology, the U.S. Army Research Office and the Tohoku University Graduate Program in Spintronics.
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Materials provided by Tohoku University. Note: Content may be edited for style and length. More
Researchers from the Paul-Drude-Institut in Berlin, the Helmholtz-Zentrum in Dresden and the Ioffe Institute in St. Petersburg have demonstrated the use of elastic vibrations to manipulate the spin states of optically active color centers in SiC at room temperature. They show a non-trivial dependence of the acoustically induced spin transitions on the spin quantization direction, which can lead to chiral spin-acoustic resonances. These findings are important for applications in future quantum-electronic devices and have recently been published in Physical Review Letters.
Color centers in solids are optically active crystallographic defects containing one or more trapped electrons. Of special interest for applications in quantum technologies are optically addressable color centers, that is, lattice defects whose electronic spin states can be selectively initialized and read-out using light. In addition to initialization and read-out, it is also necessary to develop efficient methods to manipulate their spin states, and thus the information stored in them. While this is typically realized by applying microwave fields, an alternative and more efficient method could be the use of mechanical vibrations. Among the different materials for the implementation of such strain-based technologies, SiC is attracting growing attention as a robust material for nano-electromechanical systems with an ultrahigh sensitivity to vibrations that also hosts highly-coherent optically active color centers.
In a recent work published in Physical Review Letters, researches from the Paul-Drude-Institut fuer Festkoerperelektronik, the Helmholtz-Zentrum Dresden-Rossendorf and the Ioffe Institute have demonstrated the use of elastic vibrations to manipulate the spin states of optically active color centers in SiC at room temperature. In their study, the authors use the periodic modulation of the SiC crystal lattice to induce transitions between the spin levels of the silicon-vacancy center, an optically active color center with spin S=3/2. Of special importance for future applications is the fact that, in contrast to most atom-like light centers, where the observation of strain-induced effects requires cooling the system to very low temperatures, the effects reported here were observed at room temperature.
To couple the lattice vibrations to the silicon-vacancy centers, the authors first selectively created such centers by irradiating the SiC with protons. Then they fabricated an acoustic resonator for the excitation of standing surface acoustic waves (SAW) on the SiC. SAWs are elastic vibrations confined to the surface of a solid that resemble seismic waves created during an earthquake. When the frequency of the SAW matches the resonant frequencies of the color centers, the electrons trapped in them can use the energy of the SAW to jump between the different spin sublevels. Due to the special nature of the spin-strain coupling, the SAW can induce jumps between spin states with magnetic quantum number differences ?m=±1 and ?m=±2, while microwave-induced ones are restricted to ?m=±1. This allows to realize full control of the spin states using high-frequency vibrations without the aid of external microwave fields.
In addition, due to the intrinsic symmetry of the SAW strain fields combined with the peculiar properties of the half-integer spin system, the intensity of such spin transitions depends on the angle between SAW propagation and spin quantization directions, which can be controlled by an external magnetic field. Moreover, the authors predict a chiral spin-acoustic resonance under traveling SAWs. This means that, under certain experimental conditions, the spin transitions can be switched on or off by inverting the magnetic field or the SAW propagation direction.
These findings establish silicon carbide as a highly promising hybrid platform for on-chip spin-optomechanical quantum control enabling engineered interactions at room temperature.
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Materials provided by Forschungsverbund Berlin. Note: Content may be edited for style and length. More
