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A new quantum measurement protocol

Researchers develop new measurement protocol for quantum particles

A new protocol for measurement developed at TU Wien will help in the measurement of the quantum phase of electrons. This is a significant step in attosecond physics. The work appears in the Physical Review Letters.

The current methods in attosecond physics help to measure very short intervals of time. We can track physical processes with very high precision, attoseconds to be precise which is equal to billionths of a billionth of a second.

This can be done using short laser pulses. The ionisation of one atom can be studied along with the process in which an electron exits the atom. Electrons do not always display the particle properties since the quantum-physical wave behaviour plays a major role. It is a wave oscillating in a very short time scale. The task to measure the cycle duration of such oscillations is challenging, however, it is even more difficult to measure the phase. Questions such as how would the electron waves oscillate if an electron can be ionized in two ways get quite tricky. 

A group of researchers from TU Wien and CREOL College, University of Central Florida has developed a protocol for measuring the phase of the electron waves. This can help in understanding photovoltaics in a better manner. 

Stefan Donsa, a team member working under Prof. Joachim Burgdörfer, Institute for Theoretical Physics, TU Wien mentioned that a wave consists of crests and troughs. Its phase tells the location of these points in space and time. Perfect overlapping of quantum waves, such that every wave peak meets a wave peek of other one adds up the waves, on the other hand, if the crest superimposes with the trough then they get cancelled. Hence phase shifts are very important in quantum physics. For this, a reference clock is needed that can make sure the overlap occurs at the exact time without any shift. The latest measurement protocol uses an atomic process as a reference for the other one. 

Helium atoms have been studied in computer simulations where a photon absorption results in emission of an electron. This ejected electron has a certain phase that is difficult to measure. The trick of the new method is to add a second quantum effect serving as a clock, i.e. a quantum metronome. The atom can absorb two photons instead of one under specific conditions. It leads to the same event, an electron emitted with particular energy but this can be measured as it has a different phase. Complicated protocols are needed in attosecond physics. Although there are many such protocols, none allows for the direct measurement of the phase of electron. 

Stefan Donsa said that this measurement protocol allows for the translation of information about an electron phase to its spatial distribution by a combination of special laser pulses. The right laser pulses can help in getting the phase information from the electron’s angular distribution. 

The protocols have to be experimented now to identify which quantum mechanical information can actually be obtained. 

Journal Reference: Physical Review Letters.

light rays

Researchers discover a property of light never predicted before

A team of researchers from different institutions in Spain and the USA notified that they have found a brand new property of light known as self-torque. The team’s research paper explained how they came to know about the property and what are the uses of it and their research paper was published in the journal Science.

Researchers knew about the properties of light such as wavelength before. By the property known as angular momentum scientists in the recent times came to know that lights can also be twisted. Vortex beams are that kind of beams that have highly structured angular momentum. They also have orbital angular momentum (OAM).

Vortex beams seem to be a helix which is surrounding a common center and when the beams strike a surface which is flat, they appear as doughnut-shaped. The scientists came to know about the new property of light while researching on OAM beams and while researching they found it out surprisingly where the lights were behaving in a way they had never noticed before. The scientists conducted a lot of experiments and the experiments were to fire two laser lights at the cloud formed by argon gas and by doing this it forced the beams to overlap. Thus they joined and they were emitted as a single beam from the other side of the argon cloud. The beam which resulted was a type of vortex beam.

The scientists then thought what would have happened if the lasers were a little bit out of synchronization and if the lasers had different orbital angular momentum.  After this experiment emerged a beam which looked like a corkscrew with a twist which was gradually changing. When the beam hit the flat surface it looked similar to a crescent moon.

The researchers also noticed that it can be looked the other way round as a single photon which was at the front of the beam was revolving around its center slower than a photon which was at the back of the beam. The scientists named this new property as self-torque. This is not only a newly discovered property of light, but it is also the one which was never ever predicted. This technique can be used to modulate the orbital angular momentum of light in a way very similar to that of modulating frequencies in communicating tools. This could lead to the development of devices that are used to manipulate tiny materials.

lcls SLAC National Accelerator Laboratory

Researchers produce the loudest possible sound in water

For human beings, sound is a perception of waves in the brain. However, physically it is the propagation of vibration as an audible pressure wave which requires a medium for its transmission. The medium need not be air always as loud sounds can also propagate through water.

A group of scientists of SLAC National Accelerator Laboratory, Department of Energy took an X-Ray laser to generate a very loud sound in water. The team reported that the loudness was such that it was almost at the edge of being the loudest sound which could be produced through water. The results of the experiment were reported in Physical Review Fluids. 

Physicist Claudiu Stan of Rutgers University Newark said that the produced sound was slightly below the threshold that would be enough for boiling the water. To achieve this result, scientists used an equipment known as Linac Coherent Light Source (LCLS). This is a very powerful X-ray laser which is capable of creating molecular black holes and also raise the temperature of water to 100,000 degrees celsius in a time period which is lesser than millionth of a millionth of second. The X-rays produced by the laser have very high brightness and is considered to be the most powerful X-ray source in the world.

LCLS was used by scientists to understand how the high-intensity sound waves that generate very loud sounds impact materials. For the experiment, researchers blasted very small liquid water microjets with a thickness less than hair strand in a vacuum chamber having X-ray pulses.

As the water stream was intercepted by the laser, very rapid ionisation occurred in the microjet due to heating of the water leading to its vapourisation which in turn produced shock waves.

The researchers found out that these shock waves had peak pressures which match with high sound intensity and sound pressures above 270 decibels. This is louder than a rocket launch or a jet plane taking off. It has been found that it is not possible to reach an intensity louder than this as it would result in the break down of water.

Researchers explained that the magnitudes of the sound intensity were restricted since the wave would destroy the medium of propagation though cavitation. This makes the ultrasonic waves in jets as one of the most intense sounds possible to be generated in water. Scientists also estimate these sound waves to be the highest intensity sound waves produced in water till date.



Levitating Object Using Light

Researchers devise a way to levitate objects using only light

During childhood days we have been to the magic shows and we have always wondered as to how the objects over there fly in the air. Now we know that it wasn’t magic, but it was physics applied that made it look like magic.

Now the researchers at the California Institute of Technology claim that they have found a way to levitate and propel objects using light, even though for time being the work remains theoretical. It is believed according to a paper published in Nature Photonics that this technique could be used for trajectory control of ultra-light spacecraft and even laser propelled light sails for space exploration. It means that no fuel needed, just a powerful laser fired at a spacecraft from the earth.

Scientists developed photonic levitation and propulsion system by designing a complex pattern that could be etched into an object’s surface.

The way the concentrated light beam reflected from the etching causes the object to “self-stabilize“, they say, as it attempts to stay inside the focused laser beam.

The groundwork for the new research was the development of optical tweezers and the big downside to it was that it could manipulate tiny objects at the microscopic level only.

Generic Optical Tweezer Diagram

Generic Optical Tweezer Diagram (Credit: Wikimedia)

Ognjen Ilic, post-doctoral scholar and first author of the new study, explains the tweezer concept and its limitations in much simpler terms: “One can levitate a ping pong ball using a steady stream of air from a hairdryer. But it wouldn’t work if the ping pong ball were too big, or if it were too far away from the hair dryer, and so on.

Though the theory is still untested in the real world, the researchers say that if it pans out, it could send a spacecraft to the nearest star outside our Solar System in just 20 years.

There is an audaciously interesting application to use this technique as a means for propulsion of a new generation of spacecraft,” said Harry Atwater, a professor at the Caltech Division of Engineering and Applied Science.

He also said, “We’re a long way from actually doing that, but we are in the process of testing out the principles.”

Published Research: https://www.nature.com/articles/s41566-019-0373-y