First photograph of light as a particle and a wave

Quantum mechanics tells us that light can behave simultaneously as a particle or a wave. However, there has never been an experiment able to capture both natures of light at the same time; the closest we have come is seeing either wave or particle, but always at different times. Taking a radically different experimental approach, EPFL scientists have now been able to take the first ever snapshot of light behaving both as a wave and as a particle. The breakthrough work is published in Nature Communications.

When UV light hits a metal surface, it causes an emission of electrons. Albert Einstein explained this “photoelectric” effect by proposing that light – thought to only be a wave – is also a stream of particles. Even though a variety of experiments have successfully observed both the particle- and wave-like behaviors of light, they have never been able to observe both at the same time.

A new approach on a classic effect

A research team led by Fabrizio Carbone at EPFL has now carried out an experiment with a clever twist: using electrons to image light. The researchers have captured, for the first time ever, a single snapshot of light behaving simultaneously as both a wave and a stream of particles particle.

The experiment is set up like this: A pulse of laser light is fired at a tiny metallic nanowire. The laser adds energy to the charged particles in the nanowire, causing them to vibrate. Light travels along this tiny wire in two possible directions, like cars on a highway. When waves traveling in opposite directions meet each other they form a new wave that looks like it is standing in place. Here, this standing wave becomes the source of light for the experiment, radiating around the nanowire.

This is where the experiment’s trick comes in: The scientists shot a stream of electrons close to the nanowire, using them to image the standing wave of light. As the electrons interacted with the confined light on the nanowire, they either sped up or slowed down. Using the ultrafast microscope to image the position where this change in speed occurred, Carbone’s team could now visualize the standing wave, which acts as a fingerprint of the wave-nature of light.

While this phenomenon shows the wave-like nature of light, it simultaneously demonstrated its particle aspect as well. As the electrons pass close to the standing wave of light, they “hit” the light’s particles, the photons. As mentioned above, this affects their speed, making them move faster or slower. This change in speed appears as an exchange of energy “packets” (quanta) between electrons and photons. The very occurrence of these energy packets shows that the light on the nanowire behaves as a particle.

“This experiment demonstrates that, for the first time ever, we can film quantum mechanics – and its paradoxical nature – directly,” says Fabrizio Carbone. In addition, the importance of this pioneering work can extend beyond fundamental science and to future technologies. As Carbone explains: “Being able to image and control quantum phenomena at the nanometer scale like this opens up a new route towards quantum computing.”



Cheap invisibility cloak

invisibility cloak

invisibility cloak



Hats off to scientists at the University of Rochester in New York, who have managed to produce a cheap ‘invisibility cloak’ effect using readily available materials and a lot of clever thinking. Through a combination of optical lenses, any object that passes behind a certain line of sight can be made to disappear from view.

‘The Rochester Cloak’, as it’s being dubbed, uses a simplified four-lens system that essentially bends light around any objects you put into the middle of the chain — you’re able to see the area in the background as normal, but not the item in the foreground. According to its inventors, it can be scaled up using any size of lens, and the team responsible for the setup has used standard, off-the-shelf hardware.

“People have been fascinated with cloaking for a very long time,” said John Howell, a Professor of Physics at the University. “It’s recently been a really popular thing in science fiction and Harry Potter… I think people are really excited about the prospect of just being invisible.”

“From what we know this is the first cloaking device that provides three-dimensional, continuously multidirectional cloaking,” said doctoral student Joseph Choi, one of the team who worked on the project, when speaking to Reuters. “I imagine this could be used to cloak a trailer on the back of a semi-truck so the driver can see directly behind him. It can be used for surgery, in the military, in interior design, art.”

What makes this system so interesting is that it’s simple, inexpensive and capable of working at multiple angles, as long as the object remains inside the series of lenses. Howell and Choi say it cost them $1,000 to get all of the necessary equipment together, but it can be done more cheaply. A patent is pending for their invention but the pair have put together instructions on making your own Rochester Cloak at home for less than $100.



Synthetic gel communicates with itself

In a paper published in the January 8 print edition of the Proceedings of the National Academy of Sciences, the research team demonstrates that a synthetic system can reconfigure itself through a combination of chemical communication and interaction with light.

This study demonstrates the ability of a synthetic material to actually 'talk to itself'

This study demonstrates the ability of a synthetic material to actually ‘talk to itself’

Anna Balazs, principal investigator of the study and professor of chemical and petroleum engineering in the University of Pittsburgh’s Swanson School of Engineering, has long studied the properties of the Belousov-Zhabotinsky (BZ) gel, a material first fabricated in the late 1990s and shown to pulsate in the absence of any external stimuli.

In a previous study, the team noticed that long pieces of gel attached to a surface by one end “bent” toward one another, almost as if they were trying to communicate by sending signals. This hint that “chatter” might be taking place led the team to detach the fixed ends of the gels and allow them to move freely.

Balazs and her team developed a 3D gel model to test the effects of the chemical signaling and light on the material. They found that when the gel pieces were moved far apart, they would automatically come back together, exhibiting autochemotaxis—the ability to both emit and sense a chemical, and move in response to that signal.

“This study demonstrates the ability of a synthetic material to actually ‘talk to itself’ and follow out a given action or command, similar to such biological species as amoeba and termites,” says Balazs.

“Imagine a Lego set that could by itself unsnap its parts and then put itself back together again in different shapes but also allow you to control those shapes through chemical reaction and light.”

“We find this system to be extremely exciting and important because it provides a unique opportunity to study autochemotaxis in synthetic systems,” says Olga Kuksenok, a member of the research team and research associate professor in the department of chemical engineering.

The National Science Foundation, Army Research Office, and Air Force Office of Scientific Research supported the research.