Saturday, July 23, 2016

Winding Light Takes New Paths

Light travels in a straight line. If that ceased to be the case, reflections, shadows, and really the whole world would make a lot less sense. During the past several years, however, scientists have created beams of light that curve as they travel, called accelerating beams. This crazy-sounding development could have wide ranging applications in fundamental research and practical technology, such as allowing visible light or information to be sent around obstacles.

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Friday, July 22, 2016

Experimental Results Hint at Fifth Fundamental Force

Last week, we reported on a new theory by Dr. Jonathan Feng and collaborators, slated to appear in Physical Review Letters, which postulated a fifth fundamental force of nature. Exciting as this work is, our piece contained some errors and gave altogether the wrong impression, suggesting that the experimental work that served as the basis for this new theory might not be reliable. PhysicsCentral would like to apologize to our readers for this miscommunication, and in particular to Dr. Feng, as well as to the Atomki research group whose discovery of unusual features in the decay of Beryllium-8 atoms laid the groundwork for the new theory.

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Wednesday, July 20, 2016

Microwave Technology Heats Up

Microwaves provide more than just a quick meal. The transmission of information via microwaves (the type of light, not the appliance) is fundamental to technologies such as Bluetooth communication, mobile phone networks, satellite televisions, radar, and GPS. A team of scientists from Aalto University in Finland recently created a tiny detector that could lead to big advances in microwave technology and have applications at the cutting edge of science.

The electromagnetic spectrum.
Image Credit: NASA's Imagine the Universe
Microwaves are easy to send wirelessly and transmit across a wide range of frequencies, and they pass through most objects without being affected. These features make microwaves a great option for communication systems. As the technology for sending and receiving microwave signals has improved, so have our communication abilities. However, there is still room to push the current limits on this technology.

Imagine that you are outside on a dark night when you see someone using a lantern to send out an SOS. This call for help works because you—a detector—can see the pulses of light. Now imagine that the person has a keychain flashlight instead of a lantern, so the pulses are much fainter. You can still get the message and call for help as long as you can resolve the light and dark pattern. Now imagine the signal getting fainter and fainter, until the pulses are as faint as they can possibly be—you’d need a much more sensitive detector than your eyes to register the SOS.

Similarly, over time we have developed the technology to send fainter and fainter microwave pulses—all the way down to one photon at a time. Sending messages with individual photons instead of bright pulses means you can do more communicating with less energy. This technology has exciting possibilities in communication and imaging, but also in experiments at the forefront of science that explore how atoms and molecules behave on the quantum level. The trouble is, detecting individual microwave photons efficiently is a challenge.

Scientists are approaching this challenge from multiple angles. One of the most attractive approaches is detecting microwave photons thermally—with heat. Because electromagnetic waves cause the electrons in a conductor to oscillate back and forth, there is a slight increase in the temperature of an object when it absorbs a microwave pulse. If you can detect this temperature change, congratulations! You’ve successfully detected a microwave signal.

It sounds easy enough, but in reality the change in temperature is so small than it often gets lost in the noise when you try to read out the temperature. What you need is a very sensitive thermometer that makes the temperature change easy to see. A team of scientists led by Mikko Möttönen has made significant progress toward achieving this goal.

The detector created by Möttönen’s team consists of a gold nanowire and several tiny pieces of superconducting aluminum. It is smaller than a human blood cell and is chilled to just above absolute zero. When a microwave pulse reaches the detector, it is absorbed by the nanowire and the temperature of the device goes up slightly. This leads to a change in the electrical properties of the device, making it a very sensitive thermometer.

In order to keep the small temperature change from being overwhelmed by noise, the team put a feedback mechanism in place. An external source of energy interacts with the device in such a way that when a microwave pulse is absorbed, the temperature difference is amplified, somewhat similar to the way a guitar amplifier works. The team was able to detect microwave pulses with energy 14 times smaller than previous experiments based on temperature.

Artist's depiction of a hybrid superconductor-metal microwave detector.
Image Credit: Ella Maru Sudio
The roots of the idea go back seven years to a dinnertime conversation. Möttönen was a postdoc at the Centre for Quantum Computer Technology then, eating with Jukka Pekola, a professor visiting from Aalto University. During conversation an idea sparked and some quick calculations scribbled on a small piece of paper indicated that it should be possible to detect a single microwave photon with a very sensitive thermometer. After starting at Aalto University and securing funding and expertise in the form of PhD student Joonas Govenius and postdocs Rusell Lake and Kuan Yen Tan, the experimental work began.

So far they’ve been able to detect microwave pulses of around 200 photons with 1.1 zeptojoule of energy. This is a tiny amount of energy—the energy required to lift a red blood cell by just 1 nanometer. They are working on optimizing the design, and their paper in Physical Review Letters provides some thoughts on how to get down to the individual photon level, in addition to describing their work.

“I hope that I still have somewhere the little piece of paper that we used to make the back-of-the-envelope calculations,” said Möttönen. But he continues, it’s not enough to have great ideas, you have to have a system that funds the implementation of ideas, as well as motivated, hard-working people.

In addition to other applications, this work is important for cutting-edge experiments exploring quantum-mechanical effects. Experiments in superconducting quantum computers, quantum optics, and quantum thermodynamics require detectors that can measure the energy of quantum systems, which means measuring individual microwave photons. They may sound like science fiction, but these areas could revolutionize our understanding and use of computing, light, and energy.

—Kendra Redmond
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Thursday, July 14, 2016

Did Rembrandt "Cheat"? Optics Paper Weighs in on Art History Debate

Works of art by masters like Rembrandt may have harnessed the power of light to create awe-inspiring, realistic paintings. This being Physics Buzz, artistic techniques are not really our specialty. However, it’s worth a look at the way that the scientific and artistic side of light merge in an article that just came out in the Journal of Optical Physics, published by the Institute of Physics.


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Tuesday, July 12, 2016

Ask a Physicist: Time Warp Brain Teaser

Bill, from the US, wants to know:

Would a satellite with a perfectly circular orbit around the center of a circle experience time dilation relative to an observer at the center of the circle? What if the observer were spinning to always be looking at the satellite making them both seem at relative rest? If the satellite does experience time dilation, is it due to the non-inertial acceleration due to centripetal force? 
This is a really insightful question—it applies the concepts of relativity in a very tricky way to create an apparent paradox which might not be obvious at first glance. For those less well-versed in relativity, we'll do a quick breakdown of what this question is getting at.

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Monday, July 11, 2016

Putting a New Spin on Sound Waves

It's already possible to do some really extraordinary things with sound waves, like levitating small particles and manipulating them in-air (useful for caustic chemistry reactions) but we're about to see another tool added to the sonic utility belt: spin. Scientists from Nanjing University in China have recently created a passive device that, for the first time, easily allows planar sound waves to be converted into corkscrew-shaped spiral waves without requiring elaborate geometric arrangements of sound sources.

An illustration of the new passive angular filter 

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Friday, July 08, 2016

What Most People Get Wrong About Einstein's Famous Equation

It’s practically the most famous formula in history. Every student knows it by heart, and nearly anyone can tell you who came up with it—with good reason: it’s as profound as it is widely known, communicating a fundamental truth of the universe in a mere five characters. Everyone say it with me, it’s:

E=mc2

But how many of us actually know what this means? A lot of people think they do, but—as you might expect for a concept so often-repeated but infrequently explained—a startling number of people have serious misconceptions about the significance of Einstein's most famous equation.

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Thursday, July 07, 2016

My Three Suns: Our First Look at a Triple-Star System

2016 has been an exhilarating year for space enthusiasts, and we’re only in July. Actually, this is an exhilarating year for anyone interested in where we came from and what else is out there. So far we’ve seen the first (and second) detection of gravitational waves, a rapidly expanding list of exoplanets, and Juno’s successful arrival at Jupiter’s doorstep, to name a few highlights. Today in the journal Science, astronomers announced another crazy milestone, the first image of a planet with three suns.

This image shows the newly discovered planet in the triple-star system. The picture was created from two separate SPHERE observations: one to image the three stars and one to detect the faint planet. The planet appears vastly brighter in this image than it would in reality, compared to the stars.
Image Credit: ESO/K. Wagner et al.
It sounds like science fiction, but it’s all gravity. When we talk about the Earth orbiting the Sun, most of us picture the Earth tracing out a path around the Sun while the Sun stands still. In reality, both the Sun and the Earth orbit the same point, the center of mass of the Sun-Earth system. In our case, the Sun is just so much more massive than the Earth that the center of mass and the center of the Sun are practically the same thing.

With this in mind, here is the most likely scenario: The planet orbits around a bright, heavy star. Two fainter stars are very close to each other and orbit one another. In addition, the bright star and the two faint stars are locked in an orbit around the center of mass of the triple-star system.

If this is the case, the planet is sometimes far off to one side of the system and at other times right between the bright star (its main sun) and the other two stars. The researchers estimate that for about half of the planet’s journey around its main sun, which takes around 550 years, an inhabitant looking out from his or her front porch would see three suns! Keep in mind that this is the most likely scenario—others are possible but we need more follow-up observations to know for sure.

This graphic shows the orbit of the planet (red line) and the orbits of the stars (blue lines).
Image Credit: ESO
The planet was discovered by Kevin Wagner, a PhD student at the University of Arizona, using images from the European Southern Observatory’s Very Large Telescope (VLT) in Chile. The VLT consists of four ground-based telescopes that work together in a way that provides astronomers with significantly more detail than the sum of its parts. This planet was the first one discovered with SPHERE, an instrument on one of the VLT telescopes that aims to directly image planets outside of our solar system.

Most planets outside of our solar system are detected indirectly, for example by measuring changes in the light reaching us from a star that are characteristic of planet passing in front of the star. SPHERE is more direct. Using sophisticated technology it looks at a star, filters out the light coming from the star, and produces a kind of infrared photograph of what is left. Planets give off a lot of infrared light. We can tell us quite a bit about what a planet is like by studying its infrared signal. The new planet is about four times bigger than Jupiter and approximately 1,000° F. That’s big and hot compared to our planet, but it’s actually one of the smallest and coldest planets we have imaged.

This isn’t the first triple-star system with a planet that astronomers have discovered, but we’re still in single digits. Earlier this year researchers at the Harvard-Smithsonian Center for Astrophysics announced a similar system with a stable Jupiter-like planet in its orbit. That was number four. Multi-star systems are just as common as single-star systems like ours, but it’s not clear yet how common it is that they have planets.

Compared to planets in other multiple-star systems, the newly discovered planet has a much wider orbit—meaning that it’s a lot farther from its main sun. This makes the discovery extra surprising. Scientists expect that planets in triple-star systems don’t stick around very long because as their distance from the stars changes, so does the strength of the radiation and gravity they experience. The changes are even more dramatic for planets in wider orbits. We don’t know yet how stable the orbit of this planet is, but the fact that we’ve seen it this early in the search suggests this situation may be more common or stable than previously thought. It is a good reminder that, as usual, we still have a lot more to learn!
This artist's impression shows a view of the triple-star system from close to the planet. The planet is currently known as 131399Ab and appears in the lower-left corner of the picture.
Image Credit: ESO/L. Calçada
Kendra Redmond
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Wednesday, July 06, 2016

Surprising Resonance Result Yields Record-Breaking Heat Insulation

This is an exciting time. Cutting-edge technology enables us to zoom in on individual atoms and take pictures and measurements. Theoretical models and computer simulations that describe how atoms interact on different scales are becoming more powerful. These tools are teaching us more and more about the complicated forces at work inside of materials.

One of the ultimate goals of this work is to be able to create materials by design—to decide upon the properties you want in a material for a specific application and then build it atom-by-atom or molecule-by-molecule. We aren’t there yet, but we are on our way.

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Tuesday, July 05, 2016

How to Build a Heat Engine With Guitar Strings and Levers

To most of us, a heat engine is the thing that makes our car run. A refrigerator is the appliance that keeps our milk cold. Scientists, however, tend to think about things on a much more fundamental level.

This week, a new paper by scientists from the Swiss Federal Institute of Technology (ETH) demonstrates how to build a heat engine and refrigerator using a couple of guitar strings and a lever. Their work, published in Physical Review Letters, could pave the way for new ways to produce energy and help us learn more about heat and energy on the microscopic scale.


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