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Category: quantum physics

Recently, Prof. Yang Xueming from the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences and Prof. Yang Tiangang from the Southern University of Science and Technology discussed significant advances in the study of quantum resonances in atomic and molecular collisions at near absolute zero temperature. Their article was published in Science on May 7.

The rules of quantum mechanics govern all atomic and molecular processes. Understanding the quantum nature of atomic and is essential for understanding energy transfer and chemical reaction processes, especially in the low collisional energy region, where quantum effect is the most prominent.

A remarkable feature of quantum nature in atomic and molecular collision is quantum scattering resonances, but probing them experimentally has been a great challenge due to the transient nature of these resonances.

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For the first time, researchers have succeeded in creating strong coupling between quantum systems over a great distance. They accomplished this with a novel method in which a laser loop connects the systems, enabling nearly lossless exchange of information and strong interaction between them. In the journal Science, physicists from the University of Basel and University of Hanover reported that the new method opens up new possibilities in quantum networks and quantum sensor technology.

Quantum technology is currently one of the most active fields of research worldwide. It takes advantage of the special properties of quantum mechanical states of atoms, light, or nanostructures to develop, for example, novel sensors for medicine and navigation, networks for information processing and powerful simulators for materials sciences. Generating these quantum states normally requires a between the systems involved, such as between several atoms or nanostructures.

Until now, however, sufficiently strong interactions were limited to short distances. Typically, two systems had to be placed close to each other on the same chip at low temperatures or in the same vacuum chamber, where they interact via electrostatic or magnetostatic forces. Coupling them across larger distances, however, is required for many applications such as or certain types of sensors.

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Einstein bose condensate can make ultra powerful lasers. bigsmile

The general understanding of nature involves three, sometimes four states of matter. We all are well aware of solids, liquids and gases, plus – if we think about stars – plasmas. The state in which a specific “matter” is found depends on the relation between interaction energy and temperature. In 1924, a revolutionary article was published by Bose and Einstein theoretically describing that particles should undergo a phase transition at low temperatures even if there is no or negligible interaction between them. This phase transition would not rely on an interaction between the particles but occur only due to quantum statistical effects relying on the indistinguishable nature of particles with integer spin (called bosons). This was a striking prediction and it took 71 years until this phase transition could clearly be observed in dilute atomic gases by three research groups in 1995. Only 6 years later, the Nobel Prize in physics was awarded to E. A. Cornell, W. Ketterle and C. E. Wieman “for the achievement of Bose-Einstein condensation in dilute gases of alkali atoms, and for early fundamental studies of the properties of the condensates”. The headline was simpler: “New state of matter revealed: Bose-Einstein condensate”. This was just a beginning of a still exploding research field. Not only are Bose-Einstein condensate the coldest things in universe – temperatures below one nK (1 billionth of a K above absolute zero) have been observed, they also show unique properties, e.g. behave as one giant matter wave. Weakly interacting particles with half integer spin (Fermions) do not undergo a phase transition to a Bose-Einstein condensate (BEC). Still one can cool them so far that quantum statistical effects dominate. The system is called degenerate Fermi gas (DFG) and again strange behavior occurs. Both types of degenerate quantum gases, BEC and DFG, are investigated in optical lattices to study solid state physics. New methods for precise tuning of the atomic interaction were used to study effects of High-Tc super conductivity, to create molecular BECs or to investigate dipolar BECs.

Formation of Bose-Einstein condensates

Bose-Einstein condensates (BECs) are formed if the phase space density of the atom gas becomes greater than an integer number of order one. Above this point more and more atoms occupy the lowest energy state available leading to macroscopically occupied lowest energy quantum state. A more intuitive picture is based on the wave nature of the atoms. Atoms are not point like particles. They show wave-like behavior especially at low temperature. At the transition from a thermal gas to a Bose-Einstein condensate, the size of the atomic wave packet becomes comparable to the mean distance between atoms so all atoms start to feel their common identity. In order to increase the phase space density of a laser cooled atom cloud – that is making it colder and/or more dense — one transfers the atoms into a magnetic or optical dipole trap. Further cooling is achieved by evaporative cooling taking away high energy atoms and letting the remaining ones rethermalize, quite similar to the cooling of a hot cup of coffee or tea. Typically, Bose-Einstein condensation then occurs at temperatures on the order of 0.1 µK and is observed by a characteristic change in the shape of an atom cloud that was released from the trap, illuminated with a resonant laser beam and its shadow then observed with a CCD camera.

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Exotic atoms in which electrons are replaced by other subatomic particles of the same charge allow deep insights into the quantum world. After eight years of ongoing research, a group led by Masaki Hori, senior physicist at the Max Planck Institute of Quantum Optics in Garching, Germany, has now succeeded in a challenging experiment: In a helium atom, they replaced an electron with a pion in a specific quantum state and verified the existence of this long-lived “pionic helium” for the very first time. The usually short-lived pion could thereby exist 1000 times longer than it normally would in other varieties of matter. Pions belong to an important family of particles that determine the stability and decay of atomic nuclei. The pionic helium atom enables scientists to study pions in an extremely precise manner using laser spectroscopy. The research is published in this week’s edition of Nature.

For eight years, the group worked on this challenging experiment, which has the potential to establish a new field of research. The team experimentally demonstrated for the first time that long-lived pionic really exist. “It is a form of chemical reaction that happens automatically,” explains Hori. The exotic atom was first theoretically predicted in 1964 after experiments at that time pointed toward its existence. However, it was considered extremely difficult to verify this prediction experimentally. Usually, in an atom, the extremely short-lived decays quickly. However, in pionic helium, it can be conserved in a sense so it lives 1000 times longer than it normally does in other atoms.

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Researchers at the Department of Energy’s (DOE’s) Oak Ridge National Laboratory (ORNL) have finished the preliminary commissioning of a new 14-tesla magnet at the Spallation Neutron Source (SNS). This new sample environment allows researchers to explore the fundamental physics behind complex behavior of quantum matter.

The magnet, which also features an optional dilution refrigerator insert, is the latest low-temperature sample to be commissioned at SNS. Weighing 2,670 pounds and standing nearly 7 feet tall, this massive device is an excellent tool for researchers wanting to learn more about materials that exhibit quantum phenomena. Its powerful magnetic field forces quantum particles to behave in an orderly way, giving scientists the opportunity to locate patterns in otherwise disordered . And with its refrigerator—which can chill samples to −459.65° F—scientists can essentially “freeze” molecular vibrations in materials that might appear as background noise in neutron scattering studies. This allows for more accurate measurements of the excitations associated with quantum magnets.

“Quantum systems often lack discernible order. This makes it difficult to understand their fundamental characteristics. This new sample environment lets us bring order to these systems we’re interested in studying,” said Matt Stone, a lead instrument scientist at ORNL.

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Quantum computing is seen by many as a technology of the future. In this article, we’re going to look at how to run some non-trivial programs on actual quantum computers. In particular, we’re going to discuss something called graph states. Graph states are used for quantum cryptography, quantum error correction, and measurement based quantum computing. If all of that sounds like a foreign language, that’s okay. We’re going to go through everything, from the ground up, and in detail…and don’t worry, we’ll keep it light and fun.

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Princeton researchers detect a supercurrent — a current flowing without energy loss — at the edge of a superconductor with a topological twist.

A discovery that long eluded physicists has been detected in a laboratory at Princeton. A team of physicists detected superconducting currents — the flow of electrons without wasting energy — along the exterior edge of a superconducting material. The finding was published May 1 in the journal Science.

The superconductor that the researchers studied is also a topological semi-metal, a material that comes with its own unusual electronic properties. The finding suggests ways to unlock a new era of “topological superconductivity” that could have value for quantum computing.

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Circa 2016

Researchers say the new ‘impossible’ drive could carry passengers and their equipment to the moon in as little as four hours.

A trip to Alpha Centauri, which would take tens of thousands of years now, could be reached in just 100 years.

The system is based on electromagnetic drive, or EMDrive, which converts electrical energy into thrust without the need for rocket fuel.

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Spinels are oxides with chemical formulas of the type AB2O4, where A is a divalent metal cation (positive ion), B is a trivalent metal cation, and O is oxygen. Spinels are valued for their beauty, which derives from the molecules’ spatial configurations, but spinels in which the trivalent cation B consists of the element chrome (Cr) are interesting for a reason that has nothing to do with aesthetics: They have magnetic properties with an abundance of potential technological applications, including gas sensors, drug carriers, data storage media, and components of telecommunications systems.

A study by Brazilian and Indian researchers investigated a peculiar kind of spinel: zinc-doped manganese chromite. Nanoparticles of this material, described by the formula Mn0.5 Zn0.5 Cr2O4 [where manganese (Mn) and zinc (Zn) compose the A-site divalent cation], were synthesized in the laboratory and characterized by calculations based on density functional theory (DFT), a method derived from that is used in solid-state physics and chemistry to resolve complex crystal structures.

The material’s structural, electronic, vibrational and were determined by X-ray diffraction, neutron diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy. A report of the study has been published in the Journal of Magnetism and Magnetic Materials with the title “Structural, electronic, vibrational and magnetic properties of Zn2+ substituted MnCr2O4 nanoparticles.”

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