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Qubits in quantum computing

Scientists find gravity as key to optimal quantum computation

Scientists have been trying persistently to achieve significant success in the field of Quantum Computing but still, there is a huge scope of improvement if we go by the consensus.

But recently the arduous efforts of all the involved scientists have given them something to cheer at, as there is a claim that gravity a natural phenomenon which has been studied extensively will provide the pathway through which in-depth knowledge of quantum computing can be obtained. The scientific community is hailing these findings because there is a belief that quantum computing will bring a drastic change in the power and scale of computation. The study has been published in Physical Review Letters

The reason behind this linkage between gravity and quantum computing are the geometric rules which are used for finding the shortest distance between two points on a curved surface with respect to gravity in General Relativity. Those same geometric rules can be used for finding the most effective methods to process information in quantum computing.

These points of shortest travel – whether across a spherical planet or inside a quantum computing system – are known as geodesics. A noteworthy point regarding this discovery is that it involves a branch of quantum computing which is conformal field theory. Through this new study, there is a possibility of faster calculations in the above-mentioned branch of quantum computing.

Physicist Pawel Caputa who was involved in this discovery expounds that the process of finding minimal length on complexity geometry is equivalent to solving equations of gravity. So this explanation has made it transparent about how gravity is linked to discovery of quantum computing.

Looking at the other side, there is still a requirement where the reduction of error rates should take place. Along with this, scientists are looking to bring down the interference which hinders the computation process. The reason why quantum computing is thought as the future of computing because it functions on the concept of qubits which is also another form of information. The striking feature of a qubit is its ability to represent several states in contrast to binary digits which have only two states (0 and 1).

Therefore, along with this discovery, recent progress has made quantum computing to be more space efficient and significant improvement in accuracy has taken

All of this promises a bright future for the quantum computing field but the finding has been limited and thus it requires much deeper research which will help in finding its multidisciplinary applications.

string theory

Physicist one step closer towards solution of the string theory puzzle

A physicist from the University of Colorado, Boulder is very close in solving a puzzle in the string theory which has been unsolved for more than 20 years now. 

Paul Romatschke, an associate physics professor at CU Boulder has figured out a different set of tools for what created the three-quarters dilemma. This mathematical puzzle of string theory has plagued scientists for several years. This has kept them from the realization and proof of the “Theory of everything”. The results of the study have been published in Physical Review Letters.

It may not be applicable for the regular world we see around us but it opens the possibilities for the understanding of high-level physics. The results of the study could change the ways we look at the several important domains of physics such as string theory or quantum field theory. These set of theories describe the field dynamics and the entities which permeate everything. 

Romatschke said that it would have been really great to actually understand the meaning of three-quarters however this outlook is a step towards the solution, if not the solution, and provides a suggestive picture. 

The string theory has puzzled the scientists since 1960’s. It is a theoretical framework which involves fundamental, one dimensional objects known as strings. These entities constitute the fabric of everything. It was first put forward for addressing a number of questions in fundamental physics. But from there it has been applied for studying several topics such as black holes, nuclear physics to even the origin of the universe. 

One of the biggest achievements of the string theory is the conclusion that black holes and matter are nearly the two faces of a single coin. This duality allows researchers to map several properties of matter such as pressure to the black hole properties as obtained from the general theory of relativity of Einstein. It would create the possibility of a greater mathematical exploration of the string theory. However, physicists have not been able to prove a major aspect of the string theory. 

Since the duality was discovered 20 years ago, researchers have tried to clear the roadblock with equations of increasing complexity. But they arrive at the same result always. The free energy obtained from the strong interaction is nearly three-quarters of the strength of weak coupling. 

Romatschke put the equations for space which has only two dimensions. He used equations from the previous research, as well as modern techniques of quantum field theory and he proved that a relationship exists when the matter is forced to interact from zero to infinite interaction. Calculations revealed the infinite coupling’s pressure is four-fifths of that at zero coupling. This can be a standard approach in solving puzzles of this nature. It also indicates there is a stronger relationship for space with lesser dimensions. 

 

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. 

Neural network data matching

Machine learning unlocks mysteries of quantum physics

Understanding electrons’ intricate behaviour has led to discoveries that transformed society, such as the revolution in computing made possible by the invention of the transistor.

Today, through advances in technology, electron behaviour can be studied much more deeply than in the past, potentially enabling scientific breakthroughs as world-changing as the personal computer. However, the data these tools generate are too complex for humans to interpret.

A Cornell-led team has developed a way to use machine learning to analyze the data generated by scanning tunnelling microscopy (STM) – a technique that produces subatomic scale images of electronic motions in material surfaces at varying energies, providing information unattainable by any other method.

“Some of those images were taken on materials that have been deemed important and mysterious for two decades,” said Eun-Ah Kim, professor of physics. “You wonder what kinds of secrets are buried in those images. We would like to unlock those secrets.”

Kim is senior author of “Machine Learning in Electronic Quantum Matter Imaging Experiments,” which published in Nature June 19. First authors are Yi Zhang, formerly a postdoctoral researcher in Kim’s lab and now at Peking University in China, and Andrej Mesaros, a former postdoctoral researcher in Kim’s lab now at the Université Paris-Sud in France.

Co-authors include J.C. Séamus Davis, Cornell’s James Gilbert White Distinguished Professor in the Physical Sciences, an innovator in STM-driven studies.

The research yielded new insights into how electrons interact – and showed how machine learning can be used to drive further discovery in experimental quantum physics.

At the subatomic scale, a given sample will include trillion trillions of electrons interacting with each other and the surrounding infrastructure. Electrons’ behaviour is determined partly by the tension between their two competing tendencies: to move around, associated with kinetic energy; and to stay far away from each other, associated with repulsive interaction energy.

In this study, Kim and collaborators set out to discover which of these tendencies is more important in a high-temperature superconductive material.

Using STM, electrons tunnel through a vacuum between the conducting tip of the microscope and the surface of the sample being examined, providing detailed information about the electrons’ behaviour.

“The problem is, when you take data like that and record it, you get image-like data, but it’s not a natural image, like an apple or a pear,” Kim said. The data generated by the instrument is more like a pattern, she said, and about 10,000 times more complicated than a traditional measurement curve. “We don’t have a good tool to study those kinds of data sets.”

To interpret this data, the researchers simulated an ideal environment and added factors that would cause changes in electron behaviour. They then trained an artificial neural network – a kind of artificial intelligence that can learn a specific task using methods inspired by how the brain works – to recognize the circumstances associated with different theories. When the researchers input the experimental data into the neural network, it determined which of the theories the actual data most resembled.

This method, Kim said, confirmed the hypothesis that the repulsive interaction energy was more influential in the electrons’ behaviour.

A better understanding of how many electrons interact on different materials and under different conditions will likely lead to more discoveries, she said, including the development of new materials.

“The materials that led to the initial revolution of transistors were actually pretty simple materials. Now we have the ability to design much more complex materials,” Kim said. “If these powerful tools can reveal important aspects leading to the desired property, we would like to be able to make a material with that property.”

Also contributing were researchers at Brookhaven National Laboratory, Stanford University, Harvard University, San Jose State University, the National Institute of Advanced Industrial Science in Japan, the University of Tokyo and Oxford University.

Materials provided by Cornell University

Quantum Dots

Researchers develop quantum dot microscope for measuring electric potentials of atoms

A group of scientists from Jülich in collaboration with the University of Magdeburg has developed a new technique for measuring the electric potentials of a sample with accuracy to the atomic level. Using normal methods, it was almost impossible until now to measure the electric potentials which occur in the vicinity of individual molecules. The scanning quantum dot microscopy method, which was presented in the Nature Materials journal by researchers from Forschungszentrum Jülich in collaboration with other institutes, could open new possibilities in chip manufacturing or biomolecule characterization.

All matter consists of a positive nucleus of the atom and negative electrons. They generate electric potential fields which superpose and compensate the other, even at very small distances. Conventional methods do not allow for the measurements of these fields, that are responsible for many nanoscale properties and functions. Almost all the methods which are in use today are capable of imaging potentials which are based on the forces due to the electric charges. However, these forces are difficult to distinguish from other ones occurring at the nanoscale, that prevents measurements.

Researchers from Forschungszentrum Jülich, four years ago discovered a technique based on a different principle. Scanning quantum dot microscopy involves attachment of one organic molecule, quantum dot—to atomic microscope’s tip. This molecule acts as a  probe. Dr. Christian Wagner, lead researcher at the Controlled Mechanical Manipulation of Molecules group at Peter Grünberg Institute said that due to the small size of the molecule, individual electrons can be attached from atomic microscope’s tip to the molecule in a very controlled way.

Scientists recognized that this method can open up new avenues and hence filed a patent for it. But it could not be used in real experiments immediately. Initially, there were some limitations to its practical use. But now, the electric fields of individual atoms can be visualized and also precisely quantified. This was confirmed by comparing with theoretical calculations which were done by researchers at Luxembourg. Besides this, large areas of a sample can be imaged and the nanostructures can be displayed at once.

The researchers at Jülich spent a lot of time in investigating the technique and then developed a coherent theory for it. The very sharp images are possible due to the large separation from the sample which is permitted by the microscope tip, something beyond the ability of normal atomic force microscopes.

Engineers from Otto von Guericke University, Magdeburg developed a controller for automating the repeated sequence of scanning the sample. With the controller, now simply the whole surface can be scanned in an hour, whereas earlier it took 5-6 hours for a molecule. However, preparing the atomic dot takes lots of time but scientists are optimistic in overcoming this and applying it to challenging problems.

Collage of six cluster collisions with dark matter maps

Scientists find a new candidate for dark matter along with ways to detect it

Two physicists from the University of California, Davis have got a new element for the position of dark matter and also a possible way for its detection. Their work was presented on June 6 at the Planck Conference which was held in Granada, Spain and it has also been submitted for publication in the near future.

It is estimated by researchers that dark matter comprises about a quarter of our universe, while the rest is composed of dark energy which is even more mysterious in the scientific world. Although it cannot be observed in a direct manner like normal matter, its presence can be detected through its gravity which helps in determining the shape of very distant galaxies and other such entities.

According to many researchers, dark matter is composed of an element which is yet to be identified. However the Weakly Interacting Massive Particle or WIMP has been considered as the most likely candidate for some time now. There is no clear cut definition of WIMP but it is broadly defined as a new type of elementary particle that interacts through gravity and other forces and is weaker than the weak nuclear force. Inspite of many efforts to detect it, WIMPs have not been observed in the experiments.

John Terning, a physics professor at UC Davis, who is also a coauthor of the paper said that it is not yet known for sure what is dark matter. Although WIMP was a candidate for a long time, it has been mostly ruled out. An alternative to the WIMP model is a kind of “dark electromagnetism” which includes elements such as “dark photons” and other types of particles.

In the paper, Terning along with fellow researcher Christopher Verhaaren provided a twist to the concept. It consists of a dark magnetic “monopole” interacting with dark photon. Monopole is a type of element which behaves like one end of magnet. Scientists hypothesize that dark monopoles interact with dark photons and dark electrons similar to the interaction of electrons and photons with monopoles.

The Aharonov-Bohm effect is the interference pattern in which electron when moving by a magnetic field is influenced by it while not passing through the field itself. Terning and Verhaaren remarked that a dark monopole can be detected because of the nature of shift of electrons while passing.

In a theoretical sense, the dark matter elements are passing around us all the time but to be detected in the model suggested by Terning and Verhaaren, they would have to be excited by sun. However the predicted phase shift is very small, smaller than value needed for detection of gravity waves.

Pentaquark

Evidence from Large Hadron Collider reveals structure of pentaquark

A new structure was detected from the world’s largest particle accelerator, LHC. It was an imported particle which has five quarks bounded together commonly known as pentaquark. Quarks are the subatomic particles which make protons and neutrons bind together in either pairs or triplets to form classes of particles usually known as mesons and baryon.

Recently a data analysis done at Large Hadron Collider present in Geneva, Switzerland disclosed that there are larger aggregations present like five-quark pentaquark. Scientists are collectively getting more data on the arrangement of the odd pentaquark particles. It was also seen that baryon was bounded to a meson forming an unnatural type of ghostly molecule. The study was published in the journal Physical Review Letters.

The main job of LHC machinery is accelerating packets of protons matching the speed of light and then injecting them into pairs of magnetic circles which should intersect at four points. The particles having high energy and collide with each other resulting in the release of energy and mass in the form of particles which is unreachable to earth and detectors like LHCb stays at the collision points to record the spray of particles. With the help of this data, researchers compare with laws of physics in hope to find something not observed but were theorized before.

In the year 2015 and later confirmed in 2016, researchers noticed some pairs of peaks in their analysis of data and they were surprised to see more hits in the detector than expected. The peaks showed the existence of a collection of five quarks called pentaquarks which have a mass approximately 4.5 times of a proton but the internal structure of the particle was still unknown. After researching the data, scientists noticed another pentaquark and found that one of the pentaquarks located in 2015 was two pentaquarks close in mass by that the researchers understood that peaks were very thin which means they will be able to get high-resolution measurements of the pentaquarks mass.

Heisenberg’s uncertainty principle states that there is a relationship between how well the energy of a particle can be measured and how well we can measure the time of decaying of particles and accordingly if the particles decay quickly then scientists wouldn’t have been able to observe skinny peaks and this explains the theory of how pentaquarks have long lifetime.

Tomasz Skwarnicki, a physics professor at Syracuse University said that according to this theory different particles are bonded together in some sort of unnatural molecules which exist only at the energies created in LHC and these are held by nuclear force and have no use on earth. They decay quickly but present at neutron stars. We can conclude that more experiments are required to completely know about the internal structure of pentaquarks.

Quantum Refrigerator

Scientists create superconducting quantum refrigerator

Imagine if we can think of a refrigerator so cold that it could turn atoms into their quantum states giving those properties that defy classical physics rules. In a paper published in Physical Review Applied, Andrew Jordan, physics professor at University of Rochester, and graduate student Sreenath Manikandan, along with other scientists put forward an idea that would cool atoms to nearly absolute zero temperatures and would be based on the quantum property of superconductivity which can be used to enhance the performance of quantum sensors for ultrafast computing.

The ability of a metal to conduct electricity is called conductivity. A metal with high conductivity allows electric current to flow through and offers negligible resistance to the flow of electrons. A superconductor is a scenario where the material would conduct electricity without encountering resistance and current would circulate indefinitely without any resistance. When you cool down electrons to extreme temperatures, electrons flow like a fluid without resistance. This is possible due to Cooper Pair formation at low temperatures. When you reach such low temperature, the resistance abruptly drops to zero and there is a phase transition that occurs.

Researchers could then change material into a superconducting state which is similar to material in solid, liquid or gaseous state. The operating principles of these refrigerators are quite similar to that of traditional refrigerators as both use a phase transition to get the cooling power required.

A conventional refrigerator is usually hot on the backside and operates by removing inside heat by moving a fluid called refrigerant between hot and cold reservoirs by changing the state from liquid to gas. The refrigerant in liquid form passes through expansion valve due to which there is a drop in pressure and temperature due to gaseous form. It passes through the coils absorbing heat from the system. It is again compressed into liquid by the compressor and radiating absorbed heat and the cycle is repeated however in a superconducting refrigerator instead of using a refrigerant, the electrons in the metal changes from the paired superconducting state to an unpaired normal state.

In a superconducting quantum fridge, researchers placed a layered stack of metals in a cold dilution refrigerator. The bottom layer is a sheet of superconducting niobium, the middle layer is the superconductor tantalum and the top layer is copper.

Researchers applied a current of electricity to niobium which generates a magnetic field that penetrates the layer of tantalum causing unpairing of superconducting material and causing cool down. The cold tantalum layer absorbs heat from the warmer copper layer. The magnetic field is slowly turned off causing tantalum to pair up again which causes tantalum to become hotter than niobium. The cycle repeats again which maintains a low temperature in the topmost copper layer.

 

Schrodinger cat in box

Researchers can predict the jumps of Schrodinger’s cat and save it

Researchers from Yale University have found out a way to catch and save the famous Schrodinger’s cat, by anticipating its moves beforehand and taking necessary actions to save it from its doom. Schrodinger’s cat is the symbol of quantum unpredictability that was designed by Austrian scientist, Erwin Schrödinger in the year 1935. During this entire process, scientists have managed to discard several years of dogma which was present in quantum physics.

Through this discovery, researchers can set up early warning systems for the imminent jumps made by artificial atoms which contain quantum data. The study was published in the Nature journal.

Schrodinger’s cat is a famous paradox which is designed for illustrating the superposition concept. It is the ability of two states which are unpredictable in nature to exist simultaneously. It goes like this, a cat is trapped in a box which is closed tightly. It contains a radioactive source and a poison will be triggered with the decay of a radioactive atom. With the help of quantum physics’ superposition theory we know that the cat will be both alive and dead until the box is opened by someone. By opening the box and thus making an observation, a random change in the quantum state of the cat occurs and it is either living or is dead.

The experiment which has been conducted in the laboratory of Yale professor, Michel Devoret and proposed by Zlatko Minev, the principal author studies for the first time what actually happens in a quantum jump. The results have surprisingly contradicted the view of renowned Danish physicist, Niels Bohr. 

When microscopic entities such as electrons, atoms or artificial atoms having quantum information makes a quantum jump, the transition is sudden. It occurs from one discrete state to another. These jumps were theorized by Niels Bohr about a century ago but they were observed for the first time in atoms in 1980s.

In the experiment, researchers used three microwave generators for monitoring the atom which was enclosed in a 3D aluminium cavity. It allowed the researchers to observe the atom with a very high efficiency. The microwave radiations stir the atom, which makes a jump. The quantum signal of the jump can be amplified without disturbing the room temperature. It helped the scientists to observe a sudden absence of the detection photons which are emitted by the ancillary atomic state, excited by the microwaves. This gave the warning of the jump.

Minev noted the similarity of the jump with that of the volcanic eruption. Both are unpredictable but with correct warning, the advance disaster can be detected and acted on.

Quantum network

Establishing the ultimate limits of quantum communication networks

At the moment, sensitive data is typically encrypted and then sent across fibre-optic cables and other channels together with the digital “keys” needed to decode the information. However, the data can be vulnerable to hackers.

Quantum communication takes advantage of the laws of quantum physics to protect data. These laws allow particles—typically photons of light —to transmit the data using quantum bits, or qubits.

Superior capabilities

Multinational corporations, such as IBM and Google, are now building intermediate-size quantum computers with increasing number of quantum units or qubits.

Once they scaled up to larger sizes, these devices will have far-superior capabilities than current classical computers. For instance, they may process extremely large numbers in just a few seconds, speed-up many fundamental mathematical operations, and perfectly simulate molecular and biological processes.

One challenge will be to connect quantum computers together, in order to create a quantum-version of the Internet or " quantum Internet".

However, an important but unanswered question remains: what is the ultimate rate at which one can transmit secret messages or quantum systems from one remote quantum computer to another?

Notoriously difficult

Writing in the journal Communications PhysicsProfessor Stefano Pirandola, from the University of York’s Department of Computer Science, said scientists have answered the question.

Prof Pirandola studied the optimal working mechanism of a future quantum Internet, and also provided the ultimate secret-key capacities that can potentially be achieved.

He said: “Studying quantum networks is notoriously difficult, but recent mathematical tools developed in quantum information theory have allowed us to completely simplify the analysis.

Qubits

“An outstanding question was to compute the maximum number of elementary quantum systems (known as qubits) that could be reliably transmitted from one user of the network to another, or similarly, the maximum number of completely secret bits that these remote users could share.

“This number has now a precise analytical formula.”

Furthermore, the study reveals that the classical-inspired strategy of simultaneously sending qubits through multiple routes of the network can remarkably boost the rate, i.e., the speed of the quantum communication between any two remote users.

Materials required University of York