For the longest time: Quantum computing engineers set new standard in silicon chip performance. Shri Radhe Shri Radhe...

Two milliseconds—or two thousandths of a second—is an extraordinarily long time in the world of quantum computing. On these timescales the blink of an eye—at one 10th of a second—is like an eternity..

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Now a team of researchers at UNSW Sydney has broken new ground in proving that 'spin qubits'—properties of electrons representing the basic units of information in quantum computers—can hold information for up to two milliseconds. Known as 'coherence time', the duration of time that qubits can be manipulated in increasingly complicated calculations, the achievement is 100 times longer than previous benchmarks in the same quantum processor.

"Longer coherence time means you have more time over which your quantum information is stored—which is exactly what you need when doing quantum operations," says Ph.D. student Ms Amanda Seedhouse, whose work in theoretical quantum computing contributed to the achievement.

"The coherence time is basically telling you how long you can do all of the operations in whatever algorithm or sequence you want to do before you've lost all the information in your qubits."

In quantum computing, the more you can keep spins in motion, the better the chance that the information can be maintained during calculations. When spin qubits stop spinning, the calculation collapses and the values represented by each qubit are lost. The concept of extending coherence was already confirmed experimentally by quantum engineers at UNSW in 2016..

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Indoor high-precision visible light positioning system using non-line-of-sight method.shri Radhe. Shri Radhe.. Hare Krishna...

Location-based services are becoming increasingly important in indoor environments with the development of Internet-of-thing (IoT) technologies. The visible light positioning (VLP) system offers great potential because of its immunity to radio frequency-induced electromagnetic interference, a free and unrestricted spectrum, and a much higher level of security....

The high level of security of the radio frequency....

Recently, a lot of research work on line-of sight (LOS) VLP have been demonstrated with high accuracy at very low costs. However, for LOS VLP, blocking and shadowing is a major problem; and there is the requirement for large numbers of LEDs. Few methods to solve this problem have been investigated.

In a study published in Optics Express, Dr. Lin Bangjiang's group from the Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences proposed a non-line-of sight (NLOS) VLP system using a binocular camera and a single light-emitting diode (LED). It can realize 3D high-precision positioning of an arbitrary posture by the reflected lights from the floor.

The researchers proposed a system model which consists of two function modules: a NLOS optical camera communication (OCC) module and a binocular stereo vision module. The former uses the reflections to receive the coordinate information of the LED by an improved OCC signal recovery model. And the later estimates the camera's position by a proposed binocular position estimation algorithm, which is based on the principles of binocular stereo vision.

They then proposed an error compensation algorithm to optimize the error of the system on the z-axis, which is the key problem about depth estimation for the binocular camera that the error on the z-axis is far greater than that on the x and y axes.

Additionally, the researchers designed an experimental testbed and chose a STM32 microcontroller unit to driver a LED. At the receiver, they used a binocular camera to capture the reflected lights from the ground at two different exposure modes (one long and one short).

They gained the LED position by the NLOS OCC module using the short exposure image, and got the pixel coordinates of the projection of the LED reflected by the ground in the long exposure image. An inertial measurement unit is fixed together with the binocular camera to measure its pose.

Using this information, the researchers calculated the error between the estimation value and the measured value of the camera's position.

Engineering surface atomic structures for next-generation electronics Shri Radhe Shri Radhe Shri Radhe.......

Researchers from Osaka University have found that the surface electronic structure of samarium hexaboride originating from the topology of the bulk electronic structure can be controlled by changing the surface condition. Their findings could lead to new technologies for higher speed electronics..

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Engineered surface atomic s

Researchers from Osaka University have found that the surface electronic structure of samarium hexaboride originating from the topology of the bulk electronic structure can be controlled by changing the surface condition. Their findings could lead to new technologies for higher speed electronics.

Topologically protected forms, such as a Möbius strip, are unable to be changed without breaking them via methods such as cutting. Researchers from Osaka University have developed a new means of changing surface electronic structures, detouring its topological protection.

Physicists have believed that metallic surface states of topological insulators are very stable because the surface states are protected by the wave function symmetry of the bulk electronic structure. This property is an important advantage for applied products used in various surrounding environments; however, this feature also means that it is difficult to control the surface state according to one's purpose.

"This was thought to be advantageous, such as for preventing contamination effects," says lead author Yoshiyuki Ohtsubo, "but we have found that the topologically protected surface states can be controlled by the modification of the surface symmetry without touching its inside, which will be a new control method for topological electronic states useful for quantum computing and other advanced technologies."

A ground-breaking result of this research is that the electronic structure of a slightly tilted surface from the bulk plane of symmetry of single-crystalline samarium hexaboride (SmB6) is not the same symmetry as the bulk. This result indicates that a different topological surface state has been created by fabricating this new surface atomic structure.

"In other words, the surface electronic structure and the conducting property can be controlled through fabrication methods," explains Shin-Ichi Kimura, senior author. "This will serve as a method to control topologically protected electronic structures and their physical properties."

This research result has revealed that the topological surface electronic state, which was thought to be "strictly" determined by bulk symmetry, has many degrees of freedom and can be "flexibly" controlled by manipulating the surface atomic structure. This achievement is expected to be applied to next-generation devices with low power consumption and high speed using the same electronic state, as well as to information transfer in quantum computers.

The article, "Breakdown of bulk-projected isotropy in surface electronic states of topological Kondo insulator SmB6(001)," was published in Nature Communications...

Full control of a six-qubit quantum processor in silicon. Shri Radhe Shri Radhe..

Researchers at QuTech—a collaboration between the Delft University of Technology and TNO—have engineered a record number of six, silicon-based, spin qubits in a fully interoperable array. Importantly, the qubits can be operated with a low error-rate that is achieved with a new chip design, an automated calibration procedure, and new methods for qubit initialization and readout. These advances will contribute to a scalable quantum computer based on silicon. The results are published in Nature today..

Different materials can be used to produce qubits, the quantum analog to the bit of the classical computer, but no one knows which material will turn out to be best to build a large-scale quantum computer. To date there have only been smaller demonstrations of silicon quantum chips with high quality qubit operations. Now, researchers from QuTech, led by Prof. Lieven Vandersypen, have produced a six qubit chip in silicon that operates with low error-rates. This is a major step towards a fault-tolerant quantum computer using silicon.

To make the qubits, individual electrons are placed in a linear array of six "quantum dots" spaced 90 nanometers apart. The array of quantum dots is made in a silicon chip with structures that closely resemble the transistor—a common component in every computer chip. A quantum mechanical property called spin is used to define a qubit with its orientation defining the 0 or 1 logical state. The team used finely-tuned microwave radiation, magnetic fields, and electric potentials to control and measure the spin of individual electrons and make them interact with each other.

"The quantum computing challenge today consists of two parts," explained first author Mr. Stephan Philips. "Developing qubits that are of good enough quality, and developing an architecture that allows one to build large systems of qubits. Our work fits into both categories. And since the overall goal of building a quantum computer is an enormous effort, I think it is fair to say we have made a contribution in the right direction."

The electron's spin is a delicate property. Tiny changes in the electromagnetic environment cause the direction of spin to fluctuate, and this increases the error rate. The QuTech team built upon their previous experience engineering quantum dots with new methods for preparing, controlling, and reading the spin states of electrons. Using this new arrangement of qubits, they could create logic gates and entangle systems of two or three electrons, on demand.

Quantum arrays with over 50 qubits have been produced using superconducting qubits. It is the global availability of silicon engineering infrastructure, however, that gives silicon quantum devices the promise of easier migration from research to industry. Silicon brings certain engineering challenges, and until this work from the QuTech team, only arrays of up to three qubits could be engineered in silicon without sacrificing quality.

"This paper shows that with careful engineering, it is possible to increase the silicon spin qubit count while keeping the same precision as for single qubits. The key building block developed in this research could be used to add even more qubits in the next iterations of study," said co-author Dr. Mateusz Madzik.

"In this research we push the envelope of the number of qubits in silicon, and achieve high initialization fidelities, high readout fidelities, high single-qubit gate fidelities, and high two-qubit state fidelities," said Prof. Vandersypen. "What really stands out though is that we demonstrate all these characteristics together in one single experiment on a record number of qubits.".

Shri Radhe Shri Radhe Shri Radhe Shri Radhe Silicon nanopillars for quantum communication....

Around the world, specialists are working on implementing quantum information technologies. One important path involves light: Looking ahead, single light packages, also known as light quanta or photons, could transmit data that is both coded and effectively tap proof. To this end, new photon sources are required that emit single light quanta in a controlled fashion—and on demand. Only recently has it been discovered that silicon can host sources of single-photons with properties suitable for quantum communication. So far, however, no one has known how to integrate the sources into modern photonic circuits.

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For the first time, a team led by the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) has now presented an appropriate production technology using silicon nanopillars: A chemical etching method followed by ion bombardment. Their research is published in the Journal of Applied Physics.

"Silicon and single-photon sources in the telecommunication field have long been the missing link in speeding up the development of quantum communication by optical fibers. Now we have created the necessary preconditions for it," explains Dr. Yonder Berencén of HZDR's Institute of Ion Beam Physics and Materials Research who led the current study. Although single-photon sources have been fabricated in materials like diamonds, only silicon-based sources generate light particles at the right wavelength to proliferate in optical fibers—a considerable advantage for practical purposes.

The researchers achieved this technical breakthrough by choosing a wet etching technique—what is known as MacEtch (metal-assisted chemical etching)—rather than the conventional dry etching techniques for processing the silicon on a chip. These standard methods, which allow the creation of silicon photonic structures, use highly reactive ions. These ions induce light-emitting defects caused by the radiation damage in the silicon. However, they are randomly distributed and overlay the desired optical signal with noise. Metal-assisted chemical etching, on the other hand does not generate these defects—instead, the material is etched away chemically under a kind of metallic mask.

The goal: Single photon sources compatible with the fiber-optic network

Using the MacEtch method, researchers initially fabricated the simplest form of a potential light wave-guiding structure: silicon nanopillars on a chip. They then bombarded the finished nanopillars with carbon ions, just as they would with a massive silicon block, and thus generated photon sources embedded in the pillars. Employing the new etching technique means the size, spacing, and surface density of the nanopillars can be precisely controlled and adjusted to be compatible with modern photonic circuits. Per square millimeter chip, thousands of silicon nanopillars conduct and bundle the light from the sources by directing it vertically through the pillars.

The researchers varied the diameter of the pillars because "we had hoped this would mean we could perform single defect creation on thin pillars and actually generate a single photon source per pillar," explains Berencén. "It didn't work perfectly the first time. By comparison, even for the thinnest pillars, the dose of our carbon bombardment was too high. But now it's just a short step to single photon sources."

This is a step on which the team is already working intensively because the new technique has also unleashed something of a race for future applications.

"My dream is to integrate all the elementary building blocks, from a single photon source via photonic elements through to a single photon detector, on one single chip and then connect lots of chips via commercial optical fibers to form a modular quantum network," says Berencén...

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Ultrasound technique captures micron-scale images of brain activity... Shri Radhe

Neuroimaging has increased our understanding of brain function. Such techniques often involve measuring blood flow variations to detect brain activation, exploiting the fundamental interaction between the brain’s vascular and neuronal activities. Any alterations in this so-called neurovascular coupling are strongly linked to cerebral dysfunction. The ability to image cerebral microcirculation is particularly important, as neurodegenerative diseases such as dementia and Alzheimer’s involve dysfunction of the small cerebral vessels.

Researchers at Institute Physics For Medicine Paris (Inserm/ESPCI PSL University/CNRS) have now developed a method called functional ultrasound localization microscopy (fULM) that can capture cerebral activity at the micron scale. The team published the first micron-scale, whole-brain images of rodent vascular activity in Nature Methods, along with a detailed explanation of the fULM image acquisition and analysis procedures.  

Researchers have previously used ULM to reveal microvascular anatomy at the whole-brain scale in rodents and humans. The spatial resolution of ULM is 16-fold better than that achieved with functional ultrasound imaging. But because the acquisition process is slow, ULM can only produce static maps of blood flow induced by the neuronal activity.

The fULM technique overcomes this limitation. In addition to imaging the brain microvasculature, the technique detects local brain activation by calculating the number and speed of microbubbles passing in each vessel. When a brain region activates, neurovascular coupling causes the blood volume to increase locally, dilating the vessels and allowing more microbubbles to pass. fULM provides local estimates of multiple parameters that characterize such vascular dynamics, including microbubble flow, speed and vessel diameters.

According to principal investigator Mickael Tanter and colleagues, integrating fULM into a cost-efficient, easy-to-use ultrasound scanner provides “a quantitative look at the cerebral microcirculatory network and its haemodynamic changes by combining a brain-wide spatial extent with a microscopic resolution and a 1 s temporal resolution compatible with neurofunctional imaging”.

In vivo studies

To demonstrate the fULM concept, the researchers first imaged laboratory rats with functional ultrasound (without contrast), followed by ULM in the same imaging plane. They combined sensory stimulations (whiskers deflections or visual stimulation) in anesthetized rats with continuous microbubble injection. For ULM, the rats received a continuous slow injection of microbubbles during a 20 min imaging session, leading to roughly 30 microbubbles per ultrasound frame.

During ULM processing, the researchers saved every track with each microbubble position and its respective time position. They constructed ULM images by selecting a pixel size and sorting each microbubble within each pixel. Only pixels with at least five different microbubble detections during the total acquisition time were used for analyses.

The technique allowed the researchers to map functional hyperaemia (increased blood in the vessels) in both cortical and subcortical areas with 6.5 µm resolution. They quantified the temporal haemodynamic responses during whisker stimulations for four rats and during visual stimulations for three rats, by measuring the microbubble flux and velocity.

The team quantified the involvement of blood vessels during functional hyperaemia. They observed increases in microbubble count, speed and diameter for a representative arteriole and venule (very small arteries/veins leading into/out of the capillaries), noting that control animals did not exhibit any changes. They also introduced a “perfusion” and “drainage area index” to quantify further the involvement of each individual blood vessel. These increased by 28% and 54% during stimulation for the arteriole and venule, respectively.

Due to the large field-of-view, the researchers could perform quantitative analyses simultaneously for every vessel across the whole rat brain slice image, even in deep structures such as the thalamus for whisker stimulations and superior colliculus for visual stimulations.

“The achieved spatiotemporal resolution enables fULM to image different vascular compartments in the whole brain and to discriminate their respective contributions, in particular in the precapillary arterioles known to have a major contribution to vascular changes during neuronal activities,” write the authors.

READ MORETranscranial ULM

Ultrafast ultrasound maps tiny blood vessels deep in the human brain

They add: “fULM shows that the relative increase in microbubble flow is greater in intra-parenchymal vessels rather than in arterioles. fULM also confirms depth-dependent characteristics for blood flow and speed in penetrating arterioles at baseline, and highlights a depth-dependent variation in blood speed during activation. It also quantifies large increases of microbubble flux, blood speed and diameter in venules during activation.”

As a new imaging research tool, fULM provides a way to track dynamic changes during brain activation and will offer insights into neural brain circuits. It will aid the study of functional connectivity, layer-specific cortical activity and or neurovascular coupling alterations on a brain-wide scale.

Tanter notes that researchers at Institute Physics for Medicine are collaborating with the Paris-based medical technology company Iconeus, to make this technology available for the neuroscience community and for clinical imaging very rapidly..

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It is not a good sign that Supreme Court has become the sole forum to protect personal liberty... Shri Radhe...