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Category: quantum physics

Lasers produce coherent waves of light: All the light inside a laser vibrates completely in sync. Meanwhile, quantum mechanics tells us that particles like atoms should also be thought of as waves. As a result, we can build “atom lasers” containing coherent waves of matter. But can we make these matter waves last, so that they may be used in applications? In research that was published in Nature this week, a team of Amsterdam physicists shows that the answer to this question is affirmative.

Getting bosons to march in sync

The concept that underlies the atom laser is the so-called Bose-Einstein Condensate, or BEC for short. Elementary particles in nature occur in two types: fermions and bosons. Fermions are particles like electrons and quarks—the building blocks of the matter that we are made of. Bosons are very different in nature: they are not hard like fermions, but soft: for example, they can move through one another without a problem. The best-known example of a boson is the photon, the smallest possible quantity of light. But matter particles can also combine to form bosons—in fact, entire can behave just like particles of light. What makes bosons so special is that they can all be in the exact same state at the exact same time, or phrased in more technical terms, they can “condense” into a coherent wave. When this type of condensation happens for matter particles, physicists call the resulting substance a Bose-Einstein Condensate.

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Circa 2006 string theory would explain everything even extradimensional beings or even weird phenomenon. Basically it could even explain something even greater about our existence that even a God level entity had a grand design of our universe. It could even explain miracles by these entities using string theory. Even Einstein thought that there could be a great designer and oddly enough this could explain all things in physics and our world even an infinite multiverse that our universe is much more odd then we previously thought. String theory could even essentially be the next step after quantum mechanics.

In the first part of this paper, we explain what empirical evidence points to the need for having an effective grand unification-like symmetry possessing the symmetry SU-color in 4D. If one assumes the premises of a future predictive theory including gravity — be it string/M-theory or a reincarnation — this evidence then suggests that such a theory should lead to an effective grand unification-like symmetry as above in 4D, near the string-GUT-scale, rather than the standard model symmetry. Advantages of an effective supersymmetric G(224) = SU L × SU R × SU c or SO(10) symmetry in 4D in explaining (i) observed neutrino oscillations, (ii) baryogenesis via leptogenesis, and (iii) certain fermion mass-relations are noted. And certain distinguishing tests of a SUSY G(224) or SO(10)-framework involving CP and flavor violations (as in μ → eγ, τ → μγ, edm’s of the neutron and the electron) as well as proton decay are briefly mentioned.

Recalling some of the successes we have had in our understanding of nature so far, and the current difficulties of string/M-theory as regards the large multiplicity of string vacua, some comments are made on the traditional goal of understanding vis a vis the recently evolved view of landscape and anthropism.

Invited plenary talk delivered at the International Conference on Einstein’s Legacy in the New Millennium, December 15–22, 2005, Puri, India.

Continue reading “Grand Unification as a Bridge Between String Theory And Phenomenology” | >

Circa 2019

According to string theory, all particles and fundamental forces arise from the vibrational states of tiny strings. For mathematical consistency, these strings vibrate in 10-dimensional spacetime. And for consistency with our familiar everyday experience of the universe, with three spatial dimensions and the dimension of time, the additional six dimensions are “compactified” so as to be undetectable.

Different compactifications lead to different solutions. In string theory, a “solution” implies a vacuum of spacetime that is governed by Einstein’s theory of gravity coupled to a quantum field theory. Each solution describes a unique universe, with its own set of particles, fundamental forces and other such defining properties.

Some string theorists have focused their efforts on trying to find ways to connect string theory to properties of our known, observable universe—particularly the standard model of particle physics, which describes all known particles and all their mutual forces except gravity.

Continue reading “Found: A Quadrillion Ways for String Theory to Make Our Universe” | >

After previously studying the phenomena of two sound waves in quantum liquids, scientists have now observed sound moving at two different speeds in a quantum gas.

If you were somehow immersed in the three-dimensional gas used for this study, you would hear every sound twice: each individual sound carried by two different sound waves moving at two different speeds.

This is an important development in the field of superfluidity – fluids with no viscosity that can flow without any loss of energy.

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The origin of consciousness is one of the greatest mysteries of science. One proposed solution, first suggested by Nobel Laureate and Oxford mathematician Roger Penrose and anesthesiologist Stuart Hammeroff, at Arizona State University, in Tucson, attributes consciousness to quantum computations in the brain. This in turn hinges on the notion that gravity could play a role in how quantum effects disappear, or “collapse.” But a series of experiments in a lab deep under the Gran Sasso mountains, in Italy, has failed to find evidence in support of a gravity-related quantum collapse model, undermining the feasibility of this explanation for consciousness. The result is reported in the journal Physics of Life Reviews.

“How consciousness arises in the brain is a huge puzzle,” says Catalina Curceanu, a member of the physics think tank, the Foundational Questions Institute, FQXi, and the lead physicist on the experiments at INFN in Frascati, Italy. “There are many competing ideas, but very few can be experimentally tested.”

Quantum physics famously tells us that cats can be alive and dead at the same time, at least in . Yet in practice we never see felines locked in such an unfortunate limbo state. One popular explanation for why not is because the “wavefunction” of a system–its quantum character allowing it to be in two contradictory states simultaneously–is more likely to “collapse” or be destroyed if it is more massive, leaving it in one defined state, either dead or alive, say, but not both at the same time. This model of collapse, related to gravity acting on heavy objects like cats, was invoked by Penrose and Hammeroff when developing their model of consciousness, ‘Orch OR theory’ (the Orchestrated Objective Reduction theory), in the 1990s.

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A team of researchers affiliated with multiple institutions in the U.S., including Google Quantum AI, and a colleague in Australia, has developed a theory suggesting that quantum computers should be exponentially faster on some learning tasks than classical machines. In their paper published in the journal Science, the group describes their theory and results when tested on Google’s Sycamore quantum computer. Vedran Dunjko with Leiden University City has published a Perspective piece in the same journal issue outlining the idea behind combining quantum computing with machine learning to provide a new level of computer-based learning systems.

Machine learning is a system by which computers trained with datasets make informed guesses about new data. And quantum computing involves using sub-atomic particles to represent qubits as a means for conducting applications many times faster than is possible with . In this new effort, the researchers considered the idea of running machine-learning applications on quantum computers, possibly making them better at learning, and thus more useful.

To find out if the idea might be possible, and more importantly, if the results would be better than those achieved on classical computers, the researchers posed the problem in a novel way—they devised a task that would learn via experiments repeated many times over. They then developed theories describing how a quantum system could be used to conduct such experiments and to learn from them. They found that they were able to prove that a quantum could do it, and that it could do it much better than a classical system. In fact, they found a reduction in the required number of experiments needed to learn a concept to be four orders of magnitude lower than for classical systems. The researchers then built such a system and tested it on Google’s Sycamore quantum computer and confirmed their theory.

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Researchers at Duke University and the University of Maryland have used the frequency of measurements on a quantum computer to get a glimpse into the quantum phenomena of phase changes—something analogous to water turning to steam.

By measuring the number of operations that can be implemented on a quantum computing system without triggering the collapse of its quantum state, the researchers gained insight into how other systems—both natural and computational—meet their tipping points between phases. The results also provide guidance for working to implement that will eventually enable quantum computers to achieve their full potential.

The results appeared online June 3 in the journal Nature Physics.

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Noise in an electronic circuit is a nuisance that can scramble information or reduce a detector’s sensitivity. But noise also offers a way to learn about the microscopic quantum mechanisms at play in a material or device. By measuring a circuit’s “shot noise,” a form of white noise, researchers have previously shed light on conduction in quantum Hall and spintronic systems, for instance. Now, a collaboration led by Oren Tal at the Weizmann Institute of Science, Israel, and by Dvira Segal at the University of Toronto, Canada, has shown that an easier-to-measure form of noise, called “flicker noise,” can also be a powerful probe of quantum effects [1].

Flicker noise is a type of pink noise, whose spectrum is dominated by low frequencies—the kind of noise associated with light rainfall. Flicker noise also appears in electrical circuits, but its connection to microscopic transport channels remains poorly understood. To investigate this connection, the team studied an atomic-scale junction between two wires. They modeled the electrons passing through the junction as coherent quantum-mechanical waves that scatter off fluctuating defects located near the junction. These fluctuations can represent the trapping and releasing of electrons by static defects, the movement of charged impurities between lattice sites, and the fluctuations of atoms and molecules adsorbed on surfaces.

Continue reading “Pink Noise as a Probe of Quantum Transport” | >