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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.

Diamond graphite structure

Researchers demonstrate quantum teleportation within a diamond

Researchers from the Yokohama National University have been successful in teleporting quantum information securely within the boundaries of a diamond. The implications of this study are huge in the field of quantum information technology. It defines how sensitive information can be safely shared and stored. The results of the study have been published in the journal Communications Physics

Hideo Kosaka, professor at Yokohama National University, also a co-author of the study said that the phenomenon of quantum teleportation permits the transfer of quantum information into space which cannot be normally accessed. In addition to this, it also permits the information transfer into quantum memory by not revealing or destroying the stored information. 

In the case of a diamond, this inaccessible space consisted of its carbon atoms. Since a diamond is composed of well linked, self-contained carbon atoms it has the most suitable ingredients for quantum teleportation to occur. 

In the nucleus of the carbon atom, there are six protons and six neutrons. This nucleus is surrounded by six spinning electrons. In the bonding of atoms to form a diamond a very strong lattice is formed. Although diamond can also have complex defects. When a nitrogen atom is located in one of the two adjacent vacancies where there should be a carbon atom, the defect is called a nitrogen-vacancy-center. 

When surrounded by carbon atoms, the researchers call the nucleus of a nitrogen atom a nanomagnet

For manipulation of the electron and carbon isotope in the vacancy, researchers attached a wire of the dimensions of a quarter width of a human hair to the diamond’s surface. Then the team applied a radio wave and microwave to the wire for making an oscillating magnetic field around the diamond. The microwave was manipulated for generating the optimal conditions for the transfer of quantum information in the diamond. 

Then Kosaka’s team used nitrogen nanomagnet for anchoring an electron. They forced the electron spin for entangling with a carbon nuclear spin by using radio and microwaves. The break down of the electron spin occurs under the magnetic field which has been created by the nanomagnet, making it susceptible to entanglement. 

After the entanglement of the pieces which mean that the physical characteristics cannot be described individually as they are very similar, a photon holding the quantum information is applied and is absorbed by the electron. The absorption allows the polarization state of the photon to be transferred into the carbon, which is mediated by the entangled electron, demonstrating a teleportation of information at the quantum level.

This method can take chunks of information, from one node to another in the quantum field. Researchers want to develop this method further to enable large scale quantum computation and meteorology. 

Double slit x ray simulation

Experiment proves the wave-particle duality of antimatter

Antimatter is a material which is made of not only antiparticles but also waves. However, it has been recently found that this holds true even in the case of a singular particle of antimatter. The results of the experiments have been published in the Science Advances journal.

It has been long known by physicists that almost everything in existence, from light, other energy forms to individual particles of a human body exists both in the form of particles as well as waves. This is also known as the particle-wave duality. It has been verified for microscopic elements such as electrons, protons and even atoms and molecules. However, this is not detected in macroscopic elements due to their very short wavelengths. Quantum mechanics has its foundations in this duality of matter.

Physicists now have shown that a single positron which is the antimatter twin of an electron is composed of particles as well as waves. For proving this, scientists performed a modified version of the “double-slit experiment” which was done in 1927 by Davisson and Germer to prove that electrons have both particle as well as wave nature.

In the double-slit experiment, scientists focused a stream of electrons through a plate having two slits on it, and a detector behind the plate. If electrons were only composed of particles then, then there would have been two bright lines on the detector. But this was not the case. There was a spread-out formation on the screen with alternate bright and dim lines. Hence diffraction was observed. Waves can combine or cancel each other depending on how they overlap or shift in respect to the other one, which in turn creates a pattern which is known as interference. These experiments are called interferometry.

In 1976, scientists found out how to achieve the same results with only a single electron, which brings the conclusion that even individual electrons are actually waves which can interfere with themselves.

A team of Swiss and Italian researchers have found out how to create a low energy positron beam which could be used for conducting the first antimatter form of the famous double slit experiment. When the positrons were fired through a series of multiple slits, the pattern formed by the positrons was similar to the one which would have created by waves and not particles.

This leads to a new version of the interferometry experiments. Paola Scampoli, a researcher at Politecnico of Milano said the experiment proves the quantum-mechanical origin and hence the wave nature of the positrons.