Scientists Created First Quantum Knot

Quantum knots are real

18.01.2016

Aalto University, Finland

The very first experimental observations of knots in quantum matter have just been reported in Nature Physics.

The scientists at Aalto University (Finland) and Amherst College (USA) created knotted solitary waves, or knot solitons, in the quantum-mechanical field describing a gas of superfluid atoms, also known as a Bose–Einstein condensate.

[caption id="attachment_722" align="aligncenter" width="700"]                                                                        Quantum knots are real[/caption]

In contrast to knotted ropes, the created quantum knots exist in a field that assumes a certain direction at every point of space. The field segregates into an infinite number of linked rings, each with its own field direction. The resulting structure is topologically stable as it cannot be separated without breaking the rings. In other words, one cannot untie the knot within the superfluid unless one destroys the state of the quantum matter.

– To make this discovery we exposed a Rubidium condensate to rapid changes of a specifically tailored magnetic field, tying the knot in less than a thousandth of a second. After we learned how to tie the first quantum knot, we have become rather good at it. Thus far, we have tied several hundred such knots, says Professor David Hall, Amherst College.

The scientists tied the knot by squeezing the structure into the condensate from its outskirts. This required them to initialize the quantum field to point in a particular direction, after which they suddenly changed the applied magnetic field to bring an isolated null point, at which the magnetic field vanishes, into the center of the cloud. Then they just waited for less than a millisecond for the magnetic field to do its trick and tie the knot.

–For decades, physicists have been theoretically predicting that it should be possible to have knots in quantum fields, but nobody else has been able to make one. Now that we have seen these exotic beasts, we are really excited to study their peculiar properties. Importantly, our discovery connects to a diverse set of research fields including cosmology, fusion power, and quantum computers, says research group leaderMikko Möttönen, Aalto University.

Knots have been used and appreciated by human civilizations for thousands of years. For example, they have enabled great seafaring expeditions and inspired intricate designs and patterns. The ancient Inca civilization used a system of knots known as quipu to store information. In modern times, knots have been thought to play important roles in the quantum-mechanical foundations of nature, although they have thus far remained unseen in quantum dynamics.

In everyday life, knots are typically tied on ropes or strings with two ends. However, these kinds of knots are not what mathematicians call topologically stable since they can be untied without cutting the rope. In stable knots, the ends of the ropes are glued together. Such knots can be relocated within the rope but cannot be untied without scissors.

Mathematically speaking, the created quantum knot realizes a mapping referred to as Hopf fibration that was discovered by Heinz Hopf in 1931. The Hopf fibration is still widely studied in physics and mathematics. Now it has been experimentally demonstrated for the first time in a quantum field.

–This is the beginning of the story of quantum knots. It would be great to see even more sophisticated quantum knots to appear such as those with knotted cores. Also it would be important to create these knots in conditions where the state of the quantum matter would be inherently stable. Such system would allow for detailed studies of the stability of the knot itself, says Mikko Möttönen.

News Release Source : Quantum knots are real

Image Credit : Aalto University, Finland

The research article  Link : “Tying Quantum Knots”, Nature Physics

Researchers Linked between String Field Theory and Quantum Mechanics

String field theory could be the foundation of quantum mechanics

USC scientists uncover a connection that could be a huge boost to string theory

Two USC researchers have proposed a link between string field theory and quantum mechanics that could open the door to using string field theory — or a broader version of it, called M-theory — as the basis of all physics.

[caption id="attachment_467" align="aligncenter" width="660"] Two USC researchers used string field theory to try to validate quantum mechanics.[/caption]

“This could solve the mystery of where quantum mechanics comes from,” said Itzhak Bars, USC Dornsife College of Letters, Arts and Sciences professor and lead author of the paper.

Bars collaborated with Dmitry Rychkov, his Ph.D. student at USC. The paper was published online on Oct. 27 by the journal Physics Letters.

Rather than use quantum mechanics to validate string field theory, the researchers worked backwards and used string field theory to try to validate quantum mechanics.

In their paper, which reformulated string field theory in a clearer language, Bars and Rychov showed that a set of fundamental quantum mechanical principles known as “commutation rules’’ that may be derived from the geometry of strings joining and splitting.

“Our argument can be presented in bare bones in a hugely simplified mathematical structure,” Bars said. “The essential ingredient is the assumption that all matter is made up of strings and that the only possible interaction is joining/splitting as specified in their version of string field theory.”

The history of string theory

Physicists have long sought to unite quantum mechanics and general relativity, and to explain why both work in their respective domains. First proposed in the 1970s, string theory resolved inconsistencies of quantum gravity and suggested that the fundamental unit of matter was a tiny string, not a point, and that the only possible interactions of matter are strings either joining or splitting.

Four decades later, physicists are still trying to hash out the rules of string theory, which seem to demand some interesting starting conditions to work (like extra dimensions, which may explain why quarks and leptons have electric charge, color and “flavor” that distinguish them from one another).

At present, no single set of rules can be used to explain all of the physical interactions that occur in the observable universe.

On large scales, scientists use classical, Newtonian mechanics to describe how gravity holds the moon in its orbit or why the force of a jet engine propels a jet forward. Newtonian mechanics is intuitive and can often be observed with the naked eye.

On incredibly tiny scales, such as 100 million times smaller than an atom, scientists use relativistic quantum field theory to describe the interactions of subatomic particles and the forces that hold quarks and leptons together inside protons, neutrons, nuclei and atoms.

An invaluable framework

Quantum mechanics is often counterintuitive, allowing for particles to be in two places at once, but has been repeatedly validated from the atom to the quarks. It has become an invaluable and accurate framework for understanding the interactions of matter and energy at small distances.

Quantum mechanics is extremely successful as a model for how things work on small scales, but it contains a big mystery: the unexplained foundational quantum commutation rules that predict uncertainty in the position and momentum of every point in the universe.

“The commutation rules don’t have an explanation from a more fundamental perspective, but have been experimentally verified down to the smallest distances probed by the most powerful accelerators. Clearly the rules are correct, but they beg for an explanation of their origins in some physical phenomena that are even deeper,” Bars said.

The difficulty lies in the fact that there’s no experimental data on the topic — testing things on such a small scale is currently beyond a scientist’s technological ability.

The research was funded by the Department of Energy.

News Release Source :  String field theory could be the foundation of quantum mechanics

Image Credit : Photo/astrophysics.pro

Academics are Challenging The Foundations of Quantum Science

New quantum theory is out of this parallel world

Griffith University academics are challenging the foundations of quantum science with a radical new theory based on interactions between parallel universes.

[caption id="attachment_462" align="aligncenter" width="468"] The Director of Griffith’s Centre for Quantum Dynamics,                              Professor Howard Wiseman[/caption]

In a paper published in the prestigious journal Physical Review X,Professor Howard Wiseman and Dr Michael Hall from Griffith’sCentre for Quantum Dynamics, and Dr Dirk-Andre Deckert from the University of California, take interacting parallel worlds out of the realm of science fiction and into that of hard science.

The team proposes that parallel universes really exist, and that they interact. That is, rather than evolving independently, nearby worlds influence one another by a subtle force of repulsion. They show that such an interaction could explain everything that is bizarre about quantum mechanics.

Quantum theory is needed to explain how the universe works at the microscopic scale, and is believed to apply to all matter. But it is notoriously difficult to fathom, exhibiting weird phenomena which seem to violate the laws of cause and effect.

As the eminent American theoretical physicist Richard Feynman once noted: “I think I can safely say that nobody understands quantum mechanics.”

However, the “Many-Interacting Worlds” approach developed at Griffith University provides a new and daring perspective on this baffling field.

“The idea of parallel universes in quantum mechanics has been around since 1957,” says Professor Wiseman.

“In the well-known “Many-Worlds Interpretation”, each universe branches into a bunch of new universes every time a quantum measurement is made. All possibilities are therefore realised – in some universes the dinosaur-killing asteroid missed Earth. In others, Australia was colonised by the Portuguese.

“But critics question the reality of these other universes, since they do not influence our universe at all. On this score, our “Many Interacting Worlds” approach is completely different, as its name implies.”

Professor Wiseman and his colleagues propose that:

• The universe we experience is just one of a gigantic number of worlds. Some are almost identical to ours while most are very different;


• All of these worlds are equally real, exist continuously through time, and possess precisely defined properties;


• All quantum phenomena arise from a universal force of repulsion between ‘nearby’ (i.e. similar) worlds, which tends to make them more dissimilar.

Dr Hall says the “Many-Interacting Worlds” theory may even create the extraordinary possibility of testing for the existence of other worlds.

“The beauty of our approach is that if there is just one world our theory reduces to Newtonian mechanics, while if there is a gigantic number of worlds it reproduces quantum mechanics,” he says.

“In between it predicts something new that is neither Newton’s theory nor quantum theory.

“We also believe that, in providing a new mental picture of quantum effects, it will be useful in planning experiments to test and exploit quantum phenomena.”

The ability to approximate quantum evolution using a finite number of worlds could have significant ramifications in molecular dynamics, which is important for understanding chemical reactions and the action of drugs.

Professor Bill Poirier, Distinguished Professor of Chemistry at Texas Tech University, has observed: “These are great ideas, not only conceptually, but also with regard to the new numerical breakthroughs they are almost certain to engender.”

From chemistry to quantum physics to science fiction, this theory opens new and exciting territory.

Go to:https://journals.aps.org/prx/abstract/10.1103/PhysRevX.4.041013

News Release Source :  New quantum theory is out of this parallel world

Image Credit : Centre for Quantum Dynamics, Griffith University

Quantum computing will Create Smarter and Creative Robots

Pressing The Accelerator on Quantum Robotics

Quantum computing will allow for the creation of powerful computers, but also much smarter and more creative robots than conventional ones. This was the conclusion arrived at by researchers from the Complutense University of Madrid (UCM) and Austria, who have confirmed that quantum tools help robots learn and respond much faster to the stimuli around them.

[caption id="attachment_440" align="aligncenter" width="500"] Quantum computing will Create Smarter and Creative Robots[/caption]

SINC | October 02 2014 09:00

Quantum mechanics has revolutionised the world of communications and computers by introducing algorithms which are much quicker and more secure in transferring information. Now researchers from the Complutense University of Madrid (UCM) and the University of Innsbruck (Austria) have published a study in the journal ‘Physical Review X’ which states that these tools can be used to apply to robots, automatons and the other agents that use artificial intelligence (AI).

They demonstrate for the first time that quantum machines can respond the best and act the fastest against the environment surrounding them. More specifically, they adapt to situations where the conventional ones, which are much slower, cannot finish the learning and response processes.

“In the case of very demanding and ‘impatient’ environments, the outcome is that the quantum robot can adapt itself and survive, while the classic robot is destined to collapse,” explains G. Davide Paparo and Miguel A. Martín-Delgado, the two researchers from UCM who have participated in the study.

Their theoretical work has focused on using quantum computing to accelerate ahead with one of the most difficult points to resolve in information technology: machine learning, which is used to create highly accurate models and predictions. It is applied, for example, to know how the climate or an illness will evolve or in the development of Internet search engines.

More creative quantum robots

“Building a model is actually a creative act, but conventional computers are no good at it,” says Martín-Delgado. “That is where quantum computing comes into play. The advances it brings are not only quantitative in terms of greater speed, but also qualitative: adapting better to environments where the classic agent does not survive. This means that quantum robots are more creative”.

The authors assess the scope of their study as such: “It means a step forward towards the most ambitious objective of artificial intelligence: the creation of a robot that is intelligent and creative, and that is not designed for specific tasks”.

This work comes under a new discipline, the so-called ‘quantum AI’, an area in which the company Google has started to invest millions of dollars via the creation of a specialised laboratory in collaboration with the NASA.

Referencia bibliográfica:

Giuseppe Davide Paparo, Vedran Dunjko, Adi Makmal, Miguel Angel Martin-Delgado, and Hans J. Briegel. “Quantum Speedup for Active Learning Agents”. Phys. Rev. X 4, 031002, 8 de julio de 2014.

News Release Source : Pressing the accelerator on quantum robotics

Image Credit : SINC

Quantum Cheshire Cat - Scientists Separate a Particle from itsProperties

Scientists separate a particle from its properties

Researchers from the Vienna University of Technology have performed the first separation of a particle from one of its properties. The study, carried out at the Institute Laue-Langevin (ILL) and published in Nature Communications, showed that in an interferometer a neutron's magnetic moment could be measured independently of the neutron itself, thereby marking the first experimental observation of a new quantum paradox known as the 'Cheshire Cat'. The new technique, which can be applied to any property of any quantum object, could be used to remove disturbance and improve the resolution of high precision measurements.

Diagram of Cheshire Cat Experiment

The idea of a Quantum Cheshire Cat was proposed theoretically last year. It is based on the well known character from Alice in Wonderland who can vanish leaving his smile behind. In quantum physics, the term refers to an object whose properties can be separated from its physical location so that the two can be measured at different places. While this is clearly not possible in our everyday experience, where objects are spatially linked to their properties, the laws of Quantum Mechanics allow it to be achieved.

Quantum mechanics already tells us that particles can be in different physical states at the same time, a phenomenon known as superposition. For example if a neutron beam is divided in two using a crystal, individual neutrons do not have to decide which of the two paths to take. Instead, they can travel along both paths at the same time in a quantum superposition.

"This experimental technique is called neutron interferometry", says Professor Yuji Hasegawa from the Vienna University of Technology. "It was invented here at the Atominstitut in the 1970s, and it has turned out to be the perfect tool to investigate the foundations of quantum mechanics."

To see if the same technique could separate the properties of a particle from the particle itself, Yuji Hasegawa brought together a team including colleagues Tobis Denkmayr, Hermann Geppert and Stephan Sponar from Vienna, together with Alexandre Matzkin from CNRS in France, Professor Jeff Tollaksen from Chapman University in California, and Hartmut Lemmel from the Institut Laue-Langevin to develop a brand new quantum experiment.

Their aim was to get neutrons at the ILL to travel along a different path from its magnetic moment - a property describing the particle's coupling strength to an external magnetic field. The neutron's magnetic moment has a directional preference, a property called spin. In the experiment the neutron beam was split into two paths with different spin directions. The upper beam path had a spin parallel to the neutrons' direction of flight whilst the spin of the lower beam pointed in the opposite direction.

After the two beams were recombined the experimental detector was set up so that only neutrons with spin parallel to the direction of motion - implying that those travelling along the upper path - are detected. "This is called postselection", says Hermann Geppert. "The beam contains neutrons of both spin directions, but we only detect a selection of the neutrons."

Things get tricky, when the location of the neutron spin is measured: the spin can be slightly changed using a magnetic field. When the two beams are recombined appropriately, they can amplify or cancel each other. This is exactly what can be seen in the measurement, if the magnetic field is applied at the lower beam – but that is the path, which the neutrons are actually never supposed to take. A magnetic field applied to the upper beam, on the other hand, does not have any effect.

"By preparing the neutrons in a special initial state and then postselecting them, we can achieve a situation in which both possible paths in the interferometer are important for the experiment, but in very different ways", says Tobias Denkmayr. "Along one of the paths, only an interaction with the particles themselves has an effect, but the other path is only sensitive to a magnetic spin coupling. The system behaves as if the particles were spatially separated from their properties."

The success of this unique type of quantum experiment was dependent on making so called 'weak measurements' to avoid the collapse of the superposition in accordance with the laws of quantum mechanics.

"These weak measurements give you less information," explains Hartmut Lemmel, instrument leader on S18, the ILL's crystal thermal neutron interferometer on which the Cheshire Cat was observed. "As a result you need to do lots of observations to achieve any sort of certainty that you have seen what you think you have seen. This was only possible due the strength of the neutron source available at the ILL which can uniquely provide the numbers of neutrons required to run these repeat experiments."

With their landmark observation suitably vindicated, questions turn to the potential impact of their fundamental discovery. One application might high precision measurements of quantum systems which are often affected by disturbance.

"Consider a quantum system that has two properties: you want to measure the first one very precisely but the second makes the system prone to perturbations. The two can be separated using a Quantum Cheshire Cat, and possibly the perturbation can be minimized", says Stephan Sponar.

News Release Source :  Scientists separate a particle from its properties

Physicists Take Quantum Leap Toward Ultra-Precise Measurement

University of Toronto Physicists Take Quantum Leap Toward Ultra-Precise Measurement

TORONTO, ON – For the first time, physicists at the University of Toronto (U of T) have overcome a major challenge in the science of measurement using quantum mechanics. Their work paves the way for great advances in using quantum states to enable the next generation of ultra-precise measurement technologies.

Physicists Take Quantum Leap Toward Ultra-Precise Measurement

University of Toronto physics students James Bateman (left) and Lee Rozema (right) led a study which successfully measured multiple photons in an entangled NOON state. The work paves the way for great advances in using quantum states to enable the next generation of ultra-precise measurement technologies.

"We've been able to conduct measurements using photons – individual particles of light – at a resolution unattainable according to classical physics," says Lee Rozema, a Ph.D. candidate in Professor Aephraim Steinberg's quantum optics research group in U of T's Department of Physics, and one of the lead authors along with M.Sc. candidate James Bateman of a report on the discovery published online today in Physical Review Letters. "This work opens up a path for using entangled states of light to carry out ultra-precise measurements."

Many of the most sensitive measurement techniques in existence, from ultra-precise atomic clocks to the world's largest telescopes, rely on detecting interference between waves – which occurs, for example, when two or more beams of light collide in the same space. Manipulating interference by producing photons in a special quantum state known as an "entangled" state – the sort of state famously dismissed by a skeptical Albert Einstein as implying "spooky action at a distance" – provided the result Rozema and his colleagues were looking for. The entangled state they used contains N photons which are all guaranteed to take the same path in an interferometer – either all N take the left-hand path or all N take the right-hand path, but no photons leave the pack.

The effects of interference are measured in devices known as "interferometers." It is well known that the resolution of such a device can be improved by sending more photons through it – when classical light beams are used, increasing the number of photons (the intensity of the light) by a factor of 100 can improve the resolution of an interferometer by a factor of 10. However, if the photons are prepared in a quantum-entangled state, an increase by a factor of 100 should improve the resolution by that same full factor of 100.

The scientific community already knew resolution could be improved by using entangled photons. Once scientists figured out how to entangle multiple photons the theory was proved correct but only up to a point. As the number of entangled photons rose, the odds of all photons reaching the same detector and at the same time became astronomically small, rendering the technique useless in practice.

So Rozema and his colleagues developed a way to employ multiple detectors in order to measure photons in entangled states. They designed an experimental apparatus that uses a "fibre ribbon" to collect photons and send them to an array of 11 single-photon detectors.

"This allowed us to capture nearly all of the multi-photons originally sent," says Rozema. "Sending single photons as well as two, three and four entangled photons at a time into our device produced dramatically improved resolution."

The U of T experiment built on a proposal by National University of Singapore physicist Mankei Tsang. In 2009, Tsang posited the idea of placing detectors at every possible position a photon could reach so that every possible event could be recorded, whether or not multiple photons hit the same detector. This would enable the calculation of the average position of all the detected photons, and could be done without having to discard any of them. The theory was quickly tested with two photons and two detectors by University of Ottawa physicist Robert Boyd.

"While two photons are better than one, we've shown that 11 detectors are far better than two," says Steinberg, summarising their advancement on Boyd's results. "As technology progresses, using high-efficiency detector arrays and on-demand entangled-photons sources, our techniques could be used to measure increasingly higher numbers of photons with higher resolution."

The discovery is reported in a study titled "Scalable spatial superresolution using entangled photons" published in the June 6 issue of Physical Review Letters. It is recommended as an Editor's Suggestion, and is accompanied by a commentary in the journal Physics which describes the work as a viable approach to efficiently observing superresolved spatial interference fringes that could improve the precision of imaging and lithography systems.

 News Release Source : University of Toronto Physicists Take Quantum Leap Toward Ultra-Precise Measurement