Random thoughts about random subjects… From science to literature and between manga and watercolours, passing by data science and rugby; including film, physics and fiction, programming, pictures and puns.
A laser in Shanghai, China, has set power records yet fits on tabletops.
Inside a cramped laboratory in Shanghai, China, physicist Ruxin Li and colleagues are breaking records with the most powerful pulses of light the world has ever seen. At the heart of their laser, called the Shanghai Superintense Ultrafast Laser Facility (SULF), is a single cylinder of titanium-doped sapphire about the width of a Frisbee. After kindling light in the crystal and shunting it through a system of lenses and mirrors, the SULF distills it into pulses of mind-boggling power. In 2016, it achieved an unprecedented 5.3 million billion watts, or petawatts (PW). The lights in Shanghai do not dim each time the laser fires, however. Although the pulses are extraordinarily powerful, they are also infinitesimally brief, lasting less than a trillionth of a second. The researchers are now upgrading their laser and hope to beat their own record by the end of this year with a 10-PW shot, which would pack more than 1000 times the power of all the world’s electrical grids combined.
The group’s ambitions don’t end there. This year, Li and colleagues intend to start building a 100-PW laser known as the Station of Extreme Light (SEL). By 2023, it could be flinging pulses into a chamber 20 meters underground, subjecting targets to extremes of temperature and pressure not normally found on Earth, a boon to astrophysicists and materials scientists alike. The laser could also power demonstrations of a new way to accelerate particles for use in medicine and high-energy physics. But most alluring, Li says, would be showing that light could tear electrons and their antimatter counterparts, positrons, from empty space—a phenomenon known as “breaking the vacuum.” It would be a striking illustration that matter and energy are interchangeable, as Albert Einstein’s famous E=mc2 equation states. Although nuclear weapons attest to the conversion of matter into immense amounts of heat and light, doing the reverse is not so easy. But Li says the SEL is up to the task. “That would be very exciting,” he says. “It would mean you could generate something from nothing.”
The Chinese group is “definitely leading the way” to 100 PW, says Philip Bucksbaum, an atomic physicist at Stanford University in Palo Alto, California. But there is plenty of competition. In the next few years, 10-PW devices should switch on in Romania and the Czech Republic as part of Europe’s Extreme Light Infrastructure, although the project recently put off its goal of building a 100-PW-scale device. Physicists in Russia have drawn up a design for a 180-PW laser known as the Exawatt Center for Extreme Light Studies (XCELS), while Japanese researchers have put forward proposals for a 30-PW device.
Largely missing from the fray are U.S. scientists, who have fallen behind in the race to high powers, according to a study published last month by a National Academies of Sciences, Engineering, and Medicine group that was chaired by Bucksbaum. The study calls on the Department of Energy to plan for at least one high-power laser facility, and that gives hope to researchers at the University of Rochester in New York, who are developing plans for a 75-PW laser, the Optical Parametric Amplifier Line (OPAL). It would take advantage of beamlines at OMEGA-EP, one of the country’s most powerful lasers. “The [Academies] report is encouraging,” says Jonathan Zuegel, who heads the OPAL.
Invented in 1960, lasers use an external “pump,” such as a flash lamp, to excite electrons within the atoms of a lasing material—usually a gas, crystal, or semiconductor. When one of these excited electrons falls back to its original state it emits a photon, which in turn stimulates another electron to emit a photon, and so on. Unlike the spreading beams of a flashlight, the photons in a laser emerge in a tightly packed stream at specific wavelengths.
Because power equals energy divided by time, there are basically two ways to maximize it: Either boost the energy of your laser, or shorten the duration of its pulses. In the 1970s, researchers at Lawrence Livermore National Laboratory (LLNL) in California focused on the former, boosting laser energy by routing beams through additional lasing crystals made of glass doped with neodymium. Beams above a certain intensity, however, can damage the amplifiers. To avoid this, LLNL had to make the amplifiers ever larger, many tens of centimeters in diameter. But in 1983, Gerard Mourou, now at the École Polytechnique near Paris, and his colleagues made a breakthrough. He realized that a short laser pulse could be stretched in time—thereby making it less intense—by a diffraction grating that spreads the pulse into its component colors. After being safely amplified to higher energies, the light could be recompressed with a second grating. The end result: a more powerful pulse and an intact amplifier.
No, sadly this is not a post about observing the Mpemba effect on beer. Instead is about me reading about new studies about the Mpemba effect – i.e. the effect that hot water freezes faster than lukewarm or cool water – while enjoying a cold beer.
To find the smallest of the small, it pays to dream big. The American physicists Rainer Weiss, Kip Thorne and Barry Barish shared the 2017 Nobel Prize in Physics today for their leading roles in the https://www.quantamagazine.org/gravitational-waves-discovered-at-long-last-20160211/,” tiny ripples in space-time set in motion by faraway cataclysms such as the collisions of black holes. The existence of gravitational waves was predicted a century ago by Albert Einstein, who assumed they would be far too weak to ever detect. But Weiss, Thorne, Barish and the late Scottish physicist Ronald Drever spent decades building a hypersensitive experiment that did just that, recording contractions and expansions in the fabric of space-time less than one-thousandth the width of an atomic nucleus.
“It’s really wonderful,” Weiss said after learning of the prize this morning. “But I view this more as a thing that is recognizing the work of about 1,000 people, a dedicated effort that’s been going on for, I hate to tell you, as long as 40 years.”
In the 1960s, Thorne, a black hole expert at the California Institute of Technology who is now 77, came to believe that collisions between the invisible monsters he studied should be detectable as gravitational waves. Meanwhile, across the country at the Massachusetts Institute of Technology’s https://www.quantamagazine.org/rainer-weiss-remembering-the-little-room-in-the-plywood-palace-20170615/,” Weiss, now 85, came up with the concept for how to detect them. They, along with Drever, founded in 1984 the project that became the Laser Interferometer Gravitational-Wave Observatory (LIGO). More than three decades later, in September 2015, LIGO’s two giant detectors recorded gravitational waves for the first time.
“This was a high-risk, very-high-potential-payoff enterprise,” Thorne told Quanta last year.
After LIGO’s breakthrough success, he and Weiss were seen as shoo-ins to win a physics Nobel. The committee chose to give half of the award to Weiss and split the other half between Thorne and Barish. (Drever, who died in March, was ineligible as the prize is not awarded posthumously, and the gravitational-wave discovery did not make the deadline for consideration last year.)
Barish’s recognition by the Nobel committee was harder to predict. He “was the organizational genius who made this thing go,” Thorne told Quanta. Barish, a Caltech particle physicist who is now 81, replaced the talented but discordant “troika” of Drever, Thorne and Weiss as leader of LIGO in 1994. Barish established the LIGO Scientific Collaboration, which now has more than 1,000 members, and orchestrated the construction of LIGO’s detectors in Louisiana and Washington state.
Left to right: Kip Thorne, Rainer Weiss and Barry Barish.
From left to right: Courtesy of the Caltech Alumni Association; Bryce Vickmark; R. Hahn
Weiss, Thorne and Barish — all now professors emeritus — and their LIGO collaborators have kick-started a new era of astrophysics by tuning in to these tremors in space-time geometry. As they radiate past Earth, gusts of gravitational waves alternately stretch and squeeze the four-kilometer-long arms of LIGO’s detectors by a fraction of an atom’s width. With princess-and-pea sensitivity, laser beams bouncing along both arms of the L-shape detectors overlap to reveal fleeting differences in the arms’ lengths. By studying the form of a gravitational-wave signal, scientists can extract details about the faraway, long-ago cataclysm that produced it.
Just last week, for example, LIGO announced its fourth and latest gravitational-wave detection. Its two detectors, along with a new detector in Europe called Virgo, registered the signal from two enormous black holes 1.8 billion light-years away. After circling each other for eons, the pair finally collided, radiating three suns’ worth of energy into space in the form of telltale gravitational waves.
“That would be one of the most fascinating things man could do, because it would tell you very much how the universe started,” said Weiss shortly after the announcement. “Gravitational waves, because they are so imperturbable — they go through everything — they will tell you the most information you can get about the earliest instants that go on in the universe.”
This article was updated on October 3, 2017, with additional details from the Nobel Prize announcement. It was also corrected to reflect that Rainer Weiss is now 85.
This is an exceptionally good answer to the question: “What do physicists wish the average person knew about physics?” The answer was written by Inna Vishik, Assistant Professor of Physics at the University of California, Davis.
Physics makes predictive models about the natural world based on empirical observations (experiments), mathematics, and numerical simulations. These models are called ‘theories’, but this does not mean they are speculative; physics theories explain past behavior and predict future behavior. When a previously-validated theory fails to explain the behavior in a new physical system, it doesn’t mean the theory is suddenly ‘wrong’ altogether, it means that it is inapplicable in a certain regime. It is very exciting for physicists when these exceptions are found, and it is in these holes in our models that we propel our understanding of the physical world forward.
The domain of physics is vast. Some physicists study the existing universe around us. Some study the smallest constituent particles and forces of matter in this universe. Some manipulate clusters of atoms, and some manipulate light. Some study crystalline solids and the myriad properties they can have when quadrillions of atoms and electrons are arranged in slightly different ways. Others study biological systems. This is not a full list of the many subfields in physics, but what they all have in common is they combine classical (including continuum) mechanics, quantum mechanics, statistical mechanics, general relativity, and electricity and magnetism in various configurations to explain the physical and engineered world around us.
Research in physics and other fundamental sciences play three crucial roles in an advanced society; they cement our cultural legacy by exploring one aspect of the human condition (the universe we occupy), similar to the role of the arts; they educate a portion of the work force in solving difficult, open ended problems beyond the limits of prior human innovation; they provide the seeds for future technological developments, which is often realized decades in the future in an unpredictable manner (i.e. not amenable to quarterly earnings reports). At the time of their inception, electromagnetic waves (late 19th century), quantum mechanics (early 20th century) and lasers (mid 20th century) were viewed even by their progenitors as esoteric curiosities; now they permeate our life, technology, and medicine so deeply that no one would question their practical importance. In the modern physics research era, there are newer ideas that might have an equally important impact 50 years from now, but they will never be realized without continued investment in the public good known as fundamental science.
Yesterday the 2016 Nobel Prize in Physics was announced. I immediately got a few tweets asking for more information about what these “exotic” states of matter were and explain more about them… Well in short the prize was awarded for the theoretical discoveries that help scientists understand unusual properties of materials, such as superconductivity and superfluidity, that arise at low temperatures.
The prize was awarded jointly to David J. Thouless of the University of Washington in Seattle, F. Duncan M. Haldane of Princeton University in New Jersey, and J. Michael Kosterlitz of Brown University in Rhode Island. The citation from the Swedish Academy reads: “for theoretical discoveries of topological phase transitions and topological phases of matter.”
“Topo…what?” – I hear you cry… well let us start at the beginning…
Thouless, Haldane and Kosterliz work in a field of physics known as Condensed Matter Physics and it is interested in the physical properties of “condensed” materials such as solids and liquids. You may not know it, but results from research in condensed matter physics have made it possible for you to save a lot of data in your computer’s hard drive: the discovery of giant magnetoresistance has made it possible.
The discoveries that the Nobel Committee are highlighting with the prize provide a better understanding of phases of matter such as superconductors, superfluids and thin magnetic films. The discoveries are now guiding the quest for next generation materials for electronics, quantum computing and more. They have developed mathematical models to describe the topological properties of materials in relation to other phenomena such as superconductivity, superfluidity and other peculiar magnetic properties.
Once again that word: “topology”…
So, we know that all matter is formed by atoms. Nonetheless matter can have different properties and appear in different forms, such as solid, liquid, superfluid, magnet, etc. These various forms of matter are often called states of matter or phases. According to condensed matter physics , the different properties of materials originate from the different ways in which the atoms are organised in the materials. Those different organizations of the atoms (or other particles) are formally called the orders in the materials. Topological order is a type of order in zero-temperature phase of matter (also known as quantum matter). In general, topology is the study of geometrical properties and spatial relations unaffected by the continuous change of shape or size of figures. In our case, we are talking about properties of matter that remain unchanged when the object is flattened or expanded.
Although, research originally focused on topological properties in 1-D and 2-D materials, researchers have discovered them in 3-D materials as well. These results are particularly important as they enable us to understanding “exotic” phenomena such as superconductivity, the property of matter that lets electrons travel through materials with zero resistance, and superfluidity, which lets fluids flow with zero loss of kinetic energy. Currently one of the most researched topics in the area is the study of topological insulators, superconductors and metals.
Here is a report from Physics Today about the Nobel Prize announcement:
David Thouless, Duncan Haldane, and Michael Kosterlitz are to be awarded the 2016 Nobel Prize in Physics for their work on topological phases and phase transitions, the Royal Swedish Academy of Sciences announced on Tuesday. Thouless, of the University of Washington in Seattle, will receive half the 8 million Swedish krona (roughly $925 000) prize; Haldane, of Princeton University, and Kosterlitz, of Brown University, will split the other half.
This year’s laureates used the mathematical branch of topology to make revolutionary contributions to their field of condensed-matter physics. In 1972 Thouless and Kosterlitz identified a phase transition that opened up two-dimensional systems as a playground for observing superconductivity, superfluidity, and other exotic phenomena. A decade later Haldane showed that topology is important in considering the properties of 1D chains of magnetic atoms. Then in the 1980s Thouless and Haldane demonstrated that the unusual behavior exhibited in the quantum Hall effect can emerge without a magnetic field.
From early on it was clear that the laureates’ work would have important implications for condensed-matter theory. Today experimenters are studying 2D superconductors and topological insulators, which are insulating in the bulk yet channel spin-polarized currents on their surfaces without resistance (see Physics Today, January 2010, page 33). The research could lead to improved electronics, robust qubits for quantum computers, and even an improved understanding of the standard model of particle physics.
Vortices and the KT transition
When Thouless and Kosterlitz first collaborated in the early 1970s, the conventional wisdom was that thermal fluctuations in 2D materials precluded the emergence of ordered phases such as superconductivity. The researchers, then at the University of Birmingham in England, dismantled that argument by investigating the interactions within a 2D lattice.
Thouless and Kosterlitz considered an idealized array of spins that is cooled to nearly absolute zero. At first the system lacks enough thermal energy to create defects, which in the model take the form of localized swirling vortices. Raising the temperature spurs the development of tightly bound pairs of oppositely rotating vortices. The coherence of the entire system depends logarithmically on the separation between vortices. As the temperature rises further, more vortex pairs pop up, and the separation between partners grows.
The two scientists’ major insight came when they realized they could model the clockwise and counterclockwise vortices as positive and negative electric charges. The more pairs that form, the more interactions are disturbed by narrowly spaced vortices sitting between widely spaced ones. “Eventually, the whole thing will fly apart and you’ll get spontaneous ‘ionization,’ ” Thouless told Physics Today in 2006.
That analog to ionization, in which the coherence suddenly falls off in an exponential rather than logarithmic dependence with distance, is known as the Kosterlitz–Thouless (KT) transition. (The late Russian physicist Vadim Berezinskii made a similar observation in 1970, which led some researchers to add a “B” to the transition name, but the Nobel committee notes that Berezinskii did not theorize the existence of the transition at finite temperature.)
Unlike some other phase transitions, such as the onset of ferromagnetism, no symmetry is broken. The sudden shift between order and disorder also demonstrates that superconductivity could indeed subsist in the 2D realm at temperatures below that of the KT transition. Experimenters observed the KT transition in superfluid helium-4 in 1978 and in superconducting thin films in 1981. More recently, the transition was reproduced in a flattened cloud of ultracold rubidium atoms (see Physics Today, August 2006, page 17).
A topological answer for the quantum Hall effect
Thouless then turned his attention to the quantum foundations of conductors and insulators. In 1980 German physicist Klaus von Klitzing had applied a strong magnetic field to a thin conducting film sandwiched between semiconductors. The electrons traveling within the film separated into well-organized opposing lanes of traffic along the edges (see Physics Today, June 1981, page 17). Von Klitzing had discovered the quantum Hall effect, for which he would earn the Nobel five years later.
Crucially, von Klitzing found that adjusting the strength of the magnetic field changed the conductance of his thin film only in fixed steps; the conductance was always an integer multiple of a fixed value, e2/h. That discovery proved the key for Thouless to relate the quantum Hall effect to topology, which is also based on integer steps—objects are often distinguished from each other topologically by the number of holes or nodes they possess, which is always an integer. In 1983 Thouless proposed that the electrons in von Klitzing’s experiment had formed a topological quantum fluid; the electrons’ collective behavior in that fluid, as measured by conductance, must vary in steps.
Not only did Thouless’s work explain the integer nature of the quantum Hall effect, but it also pointed the way to reproducing the phenomenon’s exotic behavior under less extreme conditions. In 1988 Haldane proposed a means for electrons to form a topological quantum fluid in the absence of a magnetic field. Twenty-five years later, researchers reported such behavior in chromium-doped (Bi,Sb)2Te3, the first observation of what is known as the quantum anomalous Hall effect.
Exploring topological materials
Around 2005, physicists began exploring the possibility of realizing topological insulators, a large family of new topological phases of matter that would exhibit the best of multiple worlds: They would robustly conduct electricity on their edges or surfaces without a magnetic field and as a bonus would divide electron traffic into lanes determined by spin. Since then experimenters have identified topological insulators in two and three dimensions, which may lead to improved electronics. Other physicists have created topological insulators that conduct sound or light, rather than electrons, on their surfaces (see Physics Today, May 2014, page 68).
Haldane’s work in the 1980s on the fractional quantum Hall effect was among the theoretical building blocks for proposals to use topologically protected excitations to build a fault-tolerant quantum computer (see Physics Today, October 2005, page 21). And his 1982 paper on magnetic chains serves as the foundation for efforts to create topologically protected excitations that behave like Majorana fermions, which are their own antiparticle. The work could lead to robust qubits for preserving the coherence of quantum information and perhaps provide particle physicists with clues as to the properties of fundamental Majorana fermions, which may or may not exist in nature.
Earlier this week I attended a talk by Sir Roger Penrose FRS in celebration of the 100th anniversary of the publication of Einstein´s General Theory of Relativity. The talk was entitled Einstein’s Amazing Theory of Gravity and it was sponsored by the London Mathematical Society (of which I am a proud member) and held at the Science Museum as part of the November Lates events. It also coincided with the 150th anniversary of the LMS!
Not only was the LMS and the Science Museum commemorating the centenary of the birth of Einstein’s Theory of General Relativity but other outlets were too. It may be difficult to put an actual date to Einstein’s work, but we know that on November 25th, 1915 Einstein presented the “final” form of his theory to the Prussian Academy of Sciences. You can find a full translation of the paper “The Field Equations of Gravitation” here. It is interesting to note that he refers to a couple of earlier papers in that work, but the one we are referring to presents the theory in full.
During his talk, Penrose indeed talked about Relativity and I would have preferred that he concentrated on the theory per se at a more introductory level, after all it was part of a public talk in the Science Museum. He talked about black holes and did not shy talking about conformal geometries for example (bravo!). He finished his talk by presenting some of his own work regarding eons and cyclical cosmology. You can get a flavour of what he talked about in this recording of a lecture he gave in 2010.
2015 has been declared the International Year of Light (IYL 2015) and with me being an optics geek, well, it was difficult to resist to enter a post about it. The IYL 2015 is a global initiative adopted by the United Nations to raise awareness of how optical technologies promote sustainable development and provide solutions to worldwide challenges in areas such as energy, education, communications, health, and sustainability.
There will be a number of event and programs run throughout the year and the aim of many of them is to promote public and political understanding of the central role of light in the modern world while also celebrating noteworthy anniversaries in 2015 – from the first studies of optics 1000 years ago to discoveries in optical communications that power the Internet today.