Rainer Weiss: 50 years of LIGO and gravitational waves..Hare Krishna hare Krishna hare Krishna

As one of the key experimentalists to conceptualize and then build one of the biggest experiments in history, Nobel-prize-winning physicist Rainer Weiss’s path to success is remarkable. Now aged 90 he talks to Sidney Perkowitz about his life and work, from the unexpected sources for scientific inspiration to the challenges of large-scale experiments.

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Down-to-earth, unassuming, and keen to discuss his research, physicist Rainer Weiss is remarkably easy to talk to. Five years ago, his work earned him half the 2017 Nobel Prize for Physics, with the other half going to Barry Barish and Kip Thorne, for “decisive contributions to the LIGO detector and the observation of gravitational waves”. The US-based Laser Interferometer Gravitational-Wave Observatory (LIGO) is where gravitational waves were first observed in 2015, definitively confirming the last remaining untested prediction from Albert Einstein’s century-old general theory of relativity.

Despite portending their existence, Einstein himself doubted that these waves would ever be observable because they are extremely weak. Weiss’s breakthrough idea of using laser interferometry finally made possible that first observation – of gravitational waves emitted from the merger of two black holes, 1.3 billion light-years away from Earth – and the many more that LIGO has since detected. It took decades of effort from Weiss, his Nobel colleagues and many others, and the discovery represented a pinnacle in physics that also ushered in a new era in astronomy. Since the advent of observational astronomy, we had been scanning the universe mostly by observing first visible light, then a broad spectrum of electromagnetic waves. Now gravitational waves were able to provide a new way of probing many cosmic phenomena. Only seven years after the birth of gravitational astronomy, it has already produced much valuable new knowledge.

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Weiss was born in Berlin, Germany on 29 September 1932, during the Nazis’ rise to power. Weiss’s father, Frederick, who Rainer describes as “an ardent and idealistic communist” from a young age, was a physician. As a Jew and an anti-Nazi communist, who had testified against a Nazi doctor accused of malpractice, Frederick was detained by the Nazis when Rainer’s mother, Gertrude, was pregnant with him. At the behest of his Christian wife, whose family had some local contacts, Frederick was released and sent to Prague. Once Rainer was born, Gertrude travelled with her new baby to join Frederick in Czechoslovakia, where the couple had another child, Sybille, in 1937.

But when the 1938 Munich Agreement allowed German troops to enter Czechoslovakia, the family had to escape once more. “We heard the decision on a radio while on vacation in Slovakia and joined a large group of people heading toward Prague to attempt to get a visa to emigrate to almost anywhere else in the world that would accept Jews,” Rainer recalls in his Nobel biography. The family moved to the US in 1939. Under the immigration law at that time, this was only possible because of Frederick’s profession and because a “very wonderful woman” as Weiss calls her, from the philanthropic Stix family of St Louis, posted a bond to guarantee that the Weisses would not be a burden to the community.

Weiss was raised in New York City, where he initially attended public school. In the fifth grade, he received a scholarship, via a local refugee relief organization to join Columbia Grammar School – a private school in mid-Manhattan, which at one time was associated with preparing students for Columbia University. Music, science and history were his favourite courses, and as a teenager he built custom high-fidelity or “hi-fi” audio systems for classical music lovers.

That interest and his own curiosity eventually brought him to physics. Seeking perfect sound reproduction, Weiss tried to electronically eliminate the background noise a phonograph needle makes as it moves along the groove in an old-fashioned record, which marred the music. But his efforts failed and he decided to go to college to learn enough to enable him to solve the problem. That education began at Massachusetts Institute of Technology (MIT) in 1950..

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Electronics to physics, via a detour

As an electrical engineering major at MIT, Weiss was expected to learn about generators and transmission lines before he could study the electronics that really interested him. This rigid plan was not to his taste, so in his second year he switched to physics, because “it had fewer requirements” and a more flexible curriculum. But that did not immediately work out either. In 1952 Weiss fell in love with a young woman, a pianist. The relationship did not end well and, heartbroken, Weiss failed all of his courses and had to leave MIT.

But all was not lost. By the spring of 1953 he returned to MIT as a technician working in the Atomic Beam Laboratory of physicist Jerrold Zacharias, who had developed the first atomic clock. “The science being done in that laboratory was exquisite,” Weiss recalls. “The experiments there were looking at the properties of isolated single atoms and molecules unperturbed by neighbouring systems. Each atom was the same as the next and it was possible to ask fundamental questions about their structure and the interactions that held them together.” What started off as a role helping grad students with their thesis projects eventually led to Weiss working directly with Zacharias on developing the caesium atomic beam clock, which would eventually go on to be adopted as the standard of time for the Bureau of Standards (now the National Institute of Standards and Technology) and the US Navy..

The escalation of spiritual knowledge through murmurings and chanting the name of Hare Krishna..

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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