Hybrid Quantum Networking...

Credit: Getty Images

Topics: Computer Science, Modern Physics, Quantum Computer, Quantum Mechanics

In a world’s first, researchers in France and the U.S. have performed a pioneering experiment demonstrating “hybrid” quantum networking. The approach, which unites two distinct methods of encoding information in particles of light called photons, could eventually allow for more capable and robust communications and computing.

Similar to how classical electronics can represent information as digital or analog signals, quantum systems can encode information as either discrete variables (DVs) in particles or continuous variables (CVs) in waves. Researchers have historically used one approach or the other—but not both—in any given system.

“DV and CV encoding have distinct advantages and drawbacks,” says Hugues de Riedmatten of the Institute of Photonic Sciences in Barcelona, who was not a part of the research. CV systems encode information in the varying intensity, or phasing, of light waves. They tend to be more efficient than DV approaches but are also more delicate, exhibiting stronger sensitivity to signal losses. Systems using DVs, which transmit information by the counting of photons, are harder to pair with conventional information technologies than CV techniques. They are also less error-prone and more fault-tolerant, however. Combining the two, de Riedmatten says, could offer “the best of both worlds.”

‘Hybrid’ Quantum Networking Demonstrated for First Time, Dhananjay Khadilkar, Scientific American

Majorana qubits...

Image Source: Link below

Topics: History, Modern Physics, Quantum Computer, Quantum Mechanics

Soon after Enrico Fermi became a professor of physics at Italy’s University of Rome in 1927, Ettore Majorana joined his research group. Majorana’s colleagues described him as humble because he considered some of his work unexceptional. For example, Majorana correctly predicted in 1932 the existence of the neutron, which he dubbed a neutral proton, based on an atomic-structure experiment by Irène Joliot-Curie and Frédéric Joliot-Curie. Despite Fermi’s urging, Majorana didn’t write a paper. Later that year James Chadwick experimentally confirmed the neutron’s existence and was awarded the 1935 Nobel Prize in Physics for the discovery.

Nevertheless, Fermi thought highly of Majorana, as is captured in the following quote: “There are various categories of scientists, people of a secondary or tertiary standing, who do their best but do not go very far. There are also those of high standing, who come to discoveries of great importance, fundamental for the development of science. But then there are geniuses like Galileo and Newton. Well, Ettore was one of them.” Majorana only wrote nine papers, and the last one, about the now-eponymous fermions, was published in 1937 at Fermi’s insistence. A few months later, Majorana took a night boat to Palermo and was never seen again.¹

In that final article, Majorana presented an alternative representation of the relativistic Dirac equation in terms of real wavefunctions. The representation has profound consequences because a real wavefunction describes particles that are their own antiparticles, unlike electrons and positrons. Since particles and antiparticles have opposite charges, fermions in his new representation must have zero charge. Majorana postulated that the neutrino could be one of those exotic fermions.

Although physicists have observed neutrinos for more than 60 years, whether Majorana’s hypothesis is true remains unclear. For example, the discovery of neutrino oscillations, which earned Takaaki Kajita and Arthur McDonald the 2015 Nobel Prize in Physics, demonstrates that neutrinos have mass. But the standard model requires that neutrinos be massless, so various possibilities have been hypothesized to explain the discrepancy. One answer could come from massive neutrinos that do not interact through the weak nuclear force. Such sterile neutrinos could be the particles that Majorana predicted. Whereas conclusive evidence for the existence of Majorana neutrinos remains elusive, researchers are now using Majorana’s idea for other applications, including exotic excitations in superconductors.

Majorana qubits for topological quantum computing, Physics Today

Ramón Aguado is a senior researcher at the Spanish National Research Council (CSIC) in Madrid.

Leo Kouwenhoven is a researcher at the Microsoft Quantum Lab Delft and a professor of applied physics at Delft University of Technology in the Netherlands.

WSMs...

Figure 1.
Spin–orbit coupling can open a bulk bandgap in materials with inverted valence and conduction bands. That gap is complete in a topological insulator, but in a Weyl semimetal, the bands still touch at certain points. Both phases also host surface states not shown here. (Adapted from ref. 4, B. Yan and C. Felser.)

Topics: Modern Physics, Particle Physics, Quantum Mechanics

When Paul Dirac introduced his famous equation for relativistic fermions in 1928, he aimed to describe one well-known particle: the electron. Shortly thereafter, Hermann Weyl observed that the equation has a special solution when the mass is set to zero. The so-called Weyl fermions embodied by that solution would be charged, like electrons, but being massless, they would travel faster and with less energy dissipation. The particles would also be chiral, like neutrinos, with each one’s handedness depending on whether its spin is aligned or antialigned with its momentum. Those features make Weyl fermions appealing candidates for use in electronic and spintronic devices.

No such elementary particle has yet been found. However, in 2015 three groups of researchers identified the first Weyl semimetal (WSM), tantalum arsenide, which hosts quasiparticles—collective excitations of electrons—with the properties of Weyl fermions.¹ A WSM must have a broken symmetry, and in TaAs, it’s inversion symmetry. Researchers, however, have continued searching for materials, particularly ferromagnetic materials, that instead rely on broken time-reversal symmetry. Tying a WSM crystal’s properties to magnetism, which can be adjusted using temperature changes or external fields, makes them potentially tunable.

Three new papers provide experimental evidence for magnetic WSMs. Yulin Chen’s team at Oxford University and Haim Beidenkopf’s team at the Weizmann Institute of Science, together with collaborators,² presented studies of Co₃Sn₂S₂, and Zahid Hasan’s group at Princeton University³ looked at Co₂MnGa. The works identify important features in the electronic structures of both materials’ bulk and surface states.

Magnetic semimetals host massless quasiparticles, Christine Middleton, Physics Today

#P4TC: Weyl Fermions...July 27, 2015

Quantum Sound...

Credit: Getty Images

Topics: Modern Physics, Phonons, Quantum Mechanics, Theoretical Physics

Researchers have gained control of the elusive “particle” of sound, the phonon. Although phonons—the smallest units of the vibrational energy that makes up sound waves—are not matter, they can be considered particles the way photons are particles of light. Photons commonly store information in prototype quantum computers, which aim to harness quantum effects to achieve unprecedented processing power. Using sound instead may have advantages, although it would require manipulating phonons on very fine scales.

Until recently, scientists lacked this ability; just detecting an individual phonon destroyed it. Early methods involved converting phonons to electricity in quantum circuits called superconducting qubits. These circuits accept energy in specific amounts; if a phonon’s energy matches, the circuit can absorb it—destroying the phonon but giving an energy reading of its presence.

In a new study, scientists at JILA (a collaboration between the National Institute of Standards and Technology and the University of Colorado Boulder) tuned the energy units of their superconducting qubit so phonons would not be destroyed. Instead the phonons sped up the current in the circuit, thanks to a special material that created an electric field in response to vibrations. Experimenters could then detect how much change in current each phonon caused.

“There’s been a lot of recent and impressive successes using superconducting qubits to control the quantum states of light. And we were curious—what can you do with sound that you can’t with light?” says Lucas Sletten of U.C. Boulder, lead author of the study published in June in Physical Review X. One difference is speed: sound travels much slower than light. Sletten and his colleagues took advantage of this to coordinate circuit-phonon interactions that sped up the current. They trapped phonons of particular wavelengths (called modes) between two acoustic “mirrors,” which reflect sound, and the relatively long time sound takes to make a round trip allowed the precise coordination. The mirrors were a hair’s width apart—similar control of light would require mirrors separated by about 12 meters.

Trapping the Tiniest Sound, Leila Sloman, Scientific American

Coherent Spookiness...

Figure 1. See link below

Topics: Entanglement, Modern Physics, Quantum Mechanics, Research, Women in Science

One of the most counterintuitive aspects of quantum mechanics is its nonlocality: the encoding of information in the correlations between widely separated particles (see, for example, Physics Today, August 2017, page 14). Typical demonstrations of spatially extended entanglement involve pairwise entangled particles produced two by two. But in the spins of atoms coupled to an optical cavity, researchers have also created massively parallel correlations, which can extend over macroscopic distances. Until recently, the dynamics that give rise to those correlations have been inferred only from global measurements, such as the total magnetization of the atomic cloud. Now Monika Schleier-Smith and colleagues at Stanford University are combining nonlocal spin interactions with the capability to locally prepare and detect the atomic spin states.

Spin excitations in a cavity hop coherently over long distances
Johanna L. Miller, Physics Today

#P4TC related links:

"Spooky Action at a Distance"...October 1, 2011
"Spukhafte Fernwirkung..."March 9, 2012

Nouveau Paradox...

Credit: Getty Images

Topics: Modern Physics, Quantum Mechanics, Schrödinger's Cat, Theoretical Physics

In the world’s most famous thought experiment, physicist Erwin Schrödinger described how a cat in a box could be in an uncertain predicament. The peculiar rules of quantum theory meant that it could be both dead and alive, until the box was opened and the cat’s state measured. Now, two physicists have devised a modern version of the paradox by replacing the cat with a physicist doing experiments—with shocking implications.

Quantum theory has a long history of thought experiments, and in most cases these are used to point to weaknesses in various interpretations of quantum mechanics. But the latest version, which involves multiple players, is unusual: it shows that if the standard interpretation of quantum mechanics is correct, then different experimenters can reach opposite conclusions about what the physicist in the box has measured. This means that quantum theory contradicts itself.

The conceptual experiment has been debated with gusto in physics circles for more than two years—and has left most researchers stumped, even in a field accustomed to weird concepts. “I think this is a whole new level of weirdness,” says Matthew Leifer, a theoretical physicist at Chapman University in Orange, California.

The authors, Daniela Frauchiger and Renato Renner of the Swiss Federal Institute of Technology (ETH) in Zurich, posted their first version of the argument online in April 2016. The final paper appears in Nature Communications on 18 September. (Frauchiger has now left academia.)

Reimagining of Schrödinger's Cat Breaks Quantum Mechanics—and Stumps Physicists, Davide Castelvecchi, Scientific American

Tunable Quantum States...

When the researchers turn an external magnetic field in different directions (indicated with arrows), they change the orientation of the linear electron flow above the kagome (six-fold) magnet, as seen in these electron wave interference patterns on the surface of a topological quantum kagome magnet. Each pattern is created by a particular direction of the external magnetic field applied on the sample.

Image by M. Z. Hasan, Jia-Xin Yin, Songtian Sonia Zhang, Princeton University

Topics: Modern Physics, Nanotechnology, Quantum Computer, Quantum Mechanics

An international team of researchers led by Princeton physicist Zahid Hasan has discovered a quantum state of matter that can be “tuned” at will — and it’s 10 times more tuneable than existing theories can explain. This level of manipulability opens enormous possibilities for next-generation nanotechnologies and quantum computing.

“We found a new control knob for the quantum topological world,” said Hasan, the Eugene Higgins Professor of Physics. “We expect this is tip of the iceberg. There will be a new subfield of materials or physics grown out of this. … This would be a fantastic playground for nanoscale engineering.”

Hasan and his colleagues, whose research appears in the current issue of Nature, are calling their discovery a “novel” quantum state of matter because it is not explained by existing theories of material properties.

Hasan discusses the discovery with Yin and Zhang in his office in Jadwin Hall.

Photo byNick Barberio, Office of Communications

Hasan’s interest in operating beyond the edges of known physics is what attracted Jia-Xin Yin, a postdoctoral research associate and one of three co-first-authors on the paper, to his lab. Other researchers had encouraged him to tackle one of the defined questions in modern physics, Yin said.

“But when I talked to Professor Hasan, he told me something very interesting,” Yin said. “He’s searching for new phases of matter. The question is undefined. What we need to do is search for the question rather than the answer.”

The classical phases of matter — solids, liquids and gases — arise from interactions between atoms or molecules. In a quantum phase of matter, the interactions take place between electrons, and are much more complex.

“This could indeed be evidence of a new quantum phase of matter — and that’s, for me, exciting,” said David Hsieh, a professor of physics at the California Institute of Technology and a 2009 Ph.D. graduate of Princeton, who was not involved in this research. “They’ve given a few clues that something interesting may be going on, but a lot of follow-up work needs to be done, not to mention some theoretical backing to see what really is causing what they’re seeing.”

Hasan has been working in the groundbreaking subfield of topological materials, an area of condensed matter physics, where his team discovered topological quantum magnets a few years ago. In the current research, he and his colleagues “found a strange quantum effect on the new type of topological magnet that we can control at the quantum level,” Hasan said.

Princeton scientists discover a ‘tunable’ novel quantum state of matter
Liz Fuller-Wright, Office of Communications, Princeton University

Bottoms Up...

Bottoms up: physicists working on the ATLAS experiment have discovered the most common Higgs decay channel. (Courtesy: Maximilien Brice/CERN)

Topics: Modern Physics, Quantum Mechanics, Quarks

Why "Quark"?

The name "quark" was taken by Murray Gell-Mann from the book "Finnegan's Wake" by James Joyce. The line "Three quarks for Muster Mark..." appears in the fanciful book. Gell-Mann received the 1969 Nobel Prize for his work in classifying elementary particles.

Source and primer: Quarks on Hyperphysics

Physicists working on the ATLAS experiment at CERN have confirmed that the Higgs boson decays to two bottom quarks. The discovery was made by combining data from two runs of the Large Hadron Collider (LHC) and was announced today at the 2018 International Conference on High Energy Physics in Seoul, Korea.

Although this decay channel should account for nearly 60% of all Higgs decays at the LHC, it had proven extremely difficult to spot it amongst the vast number of particles that are produced by proton-proton collisions at the collider.

Predicted in 1964, the Higgs boson was discovered in 2012 at the LHC where it is produced in high-energy proton-proton collisions.

Higgs boson seen decaying to two bottom quarks, Hamish Johnston, Physics World

Atomically Precise Manufacturing...

Credit: University of Texas at Dallas

Topics: Instrumentation, Modern Physics, Nanotechnology, Quantum Mechanics, Scanning Tunneling Microscopy

A University of Texas at Dallas graduate student, his advisor and industry collaborators believe they have addressed a long-standing problem troubling scientists and engineers for more than 35 years: How to prevent the tip of a scanning tunneling microscope from crashing into the surface of a material during imaging or lithography.

Details of the group's solution appeared in the January issue of the journal Review of Scientific Instruments, which is published by the American Institute of Physics.

Scanning tunneling microscopes (STMs) operate in an ultra-high vacuum, bringing a fine-tipped probe with a single atom at its apex very close to the surface of a sample. When voltage is applied to the surface, electrons can jump or tunnel across the gap between the tip and sample.

"Think of it as a needle that is very sharp, atomically sharp," said Farid Tajaddodianfar, a mechanical engineering graduate student in the Erik Jonsson School of Engineering and Computer Science. "The microscope is like a robotic arm, able to reach atoms on the sample surface and manipulate them."

The problem is, sometimes the tungsten tip crashes into the sample. If it physically touches the sample surface, it may inadvertently rearrange the atoms or create a "crater," which could damage the sample. Such a "tip crash" often forces operators to replace the tip many times, forfeiting valuable time.

Dr. John Randall is an adjunct professor at UT Dallas and president of Zyvex Labs, a Richardson, Texas-based nanotechnology company specializing in developing tools and products that fabricate structures atom by atom. Zyvex reached out to Dr. Reza Moheimani, a professor of mechanical engineering, to help address STMs' tip crash problem. Moheimani's endowed chair was a gift from Zyvex founder James Von Ehr MS'81, who was honored as a distinguished UTD alumnus in 2004.

"What they're trying to do is help bring atomically precise manufacturing into reality," said Randall, who co-authored the article with Tajaddodianfar, Moheimani and Zyvex Labs' James Owens. "This is considered the future of nanotechnology, and it is extremely important work."

Microscopy breakthrough paves the way for atomically precise manufacturing, The University of Texas at Dallas

Muon Magnetic Moment...

The g-2 magnet arrives at Fermilab to be installed in the Muon g-2 experiment (Courtesy: Fermilab)

Topics: Modern Physics, Particle Physics, Quantum Mechanics

Physicists in Japan say they have a solution to a problem that has puzzled particle physicists for nearly two decades – the anomalous magnetic moment of the muon.

Measurements made over several years at the at the g-2 experiment at the US’s Brookhaven National Laboratory suggest that the muon magnetic moment is significantly larger than predicted by the Standard Model of particle physics. After careful analysis of data related to the decay of the muon to an electron, the statistical significance of this discrepancy is at 3.6σ – which means that it is extremely unlikely to be a fluke.

One possible explanation is that particles not described by the Standard Model are involved in the muon decay, and their presence affects the measured value of the muon magnetic moment. Finding evidence for such particles would be a colossal achievement, which is why the new Muon g-2 experiment at Fermilab is gathering data this year.

Now, however, Takahiro Morishima of Nagoya University and Toshifumi Futamase of Kyoto Sangyo University have come up with an alternative explanation of the anomaly. In three preprints uploaded to the arXiv server, the duo calculate that effects due the curvature of space-time could result in an increase in the measured value of the magnetic moment. This effect of general relativity is related to the gravitational field of the Earth.

Has the muon magnetic moment mystery been solved? Hamish Johnston, Physics World

Nanosensors...

Semiconductor nanorods will help monitor neural activities in the future. Courtesy: Y Kuo and S Sasaki / University of California, Los Angeles

Topics: Biology, Modern Physics, Nanotechnology, Semiconductor Technology

Researchers in the US have developed nanosensors that can be directly inserted into a cell’s lipid membrane and be used to measure membrane potential. The devices, which are based on inorganic semiconductor nanoparticles, could potentially record action potentials from multiple neurons as well as electrical signals on the nanoscale – for example, across just one synapse.

Thanks to recent advances in inorganic colloidal synthesis, researchers can now make functional semiconductor nanoparticles whose size, shape and composition can be precisely controlled. Such nanoparticles can be used in applications as diverse as optoelectronics, biological imaging, sensing, catalysis and energy harvesting.

These nanomaterials can also be combined with biological cells to make highly sophisticated hybrid nanomaterials that outperform their purely biological counterparts. Until now, however, incorporating these particles into cell membranes has proved difficult. This is because they are often too big and have surface properties that can lead to non-specific binding on cell membranes. What is more, inserting nanoparticles into membrane bilayers is further complicated by the fact that their surfaces need to be functionalized so that the particles are inserted in the correct orientation.

Semiconductor nanosensor measures membrane potential, Belle Dumé, Nanotechweb.org

BEC in the Blink of an Eye...

Credit: NIST

Topics: Bose-Einstein Condensate, Modern Physics, Quantum Mechanics

It’s been more than two decades since Carl Wieman and Eric Cornell created the first Bose–Einstein condensate (BEC), confirming the counterintuitive prediction that a macroscopic population of atoms can pile into a single quantum ground state if cooled below some critical temperature. In all those years, the recipe for creating the condensates has hardly changed: Laser Doppler cooling chills the cloud of atoms as close to the critical temperature as possible; when that technique can go no further, evaporative cooling does the rest. But the evaporative cooling step is inefficient. It works by jettisoning most of a cloud’s atoms in order to cool the remaining few—a relatively slow process that can take a minute or more. Now MIT researchers led by Vladan Vuletić have come up with an alternative approach that allows them to create BECs in a fraction of the time.

Bose–Einstein condensation in the blink of an eye, Ashley G. Smart, Physics Today

A Slight Chance of Antimatter...

A Kyoto University-based team has unraveled the mystery of gamma-ray emission cascades caused by lightning strikes. Credit: Kyoto University/Teruaki Enoto

Topics: Modern Physics, Particle Physics, Research, Weather

A storm system approaches: the sky darkens, and the low rumble of thunder echoes from the horizon. Then without warning... Flash! Crash!—lightning has struck.

This scene, while familiar to anyone and repeated constantly across the planet, is not without a feeling of mystery. But now that mystery has deepened, with the discovery that lightning can result in matter-antimatter annihilation.

In a collaborative study appearing in Nature, researchers from Japan describe how gamma rays from lightning react with the air to produce radioisotopes and even positrons—the antimatter equivalent of electrons.

"We already knew that thunderclouds and lightning emit gamma rays, and hypothesized that they would react in some way with the nuclei of environmental elements in the atmosphere," explains Teruaki Enoto from Kyoto University, who leads the project.

Lightning, with a chance of antimatter, Kyoto University, Japan, Phys.org

Muons of Khufu...

Virtual-reality representation of the interior of Khufu's Pyramid. The small structure with the peaked roof near the bottom of the pyramid is the Queen's Chamber where the emulsion and hodoscope detectors were installed. The large inclined structure is the Great Gallery, which leads to King's Chamber. The new void is the white region above the Great Gallery. (Courtesy: ScanPyramids)

Topics: History, Modern Physics, Particle Physics

A large void hidden deep within Khufu's Pyramid at Giza in Egypt has been discovered by a team of physicists. The first-ever image of the mysterious structure was taken using muons that shower down on Earth after being created when cosmic rays collide with the atmosphere.

The measurements were done by the ScanPyramids collaboration that includes researchers from Egypt, Japan and France. The team used three different muon-imaging techniques to study the pyramid, which was built in about 2500 BCE and is also known as the Great Pyramid and the Pyramid of Cheops.

Called muography, the technique is similar to radiography using X-rays. Dense materials such as stone tend to absorb muons, which travel relatively unhindered through the air. If more muons than expected reach a detector within the pyramid, it means that they must have passed through an air-filled void on their way.

To verify the existence of the void, scientists from the KEK particle physics lab in Japan installed hodoscopes at a separate location within the Queen's Chamber. These comprise layers of plastic scintillator, which measure muon trajectories. Outside the pyramid, physicists from France's nuclear research agency CEA monitored the muon flux through the pyramid using micromegas detectors. These were arranged in muon "telescopes", which are also able to measure muon trajectories.

Muons reveal hidden void in Egyptian pyramid, Hamish Johnston, Physics World

Atoms and Josephson Junctions...

An electron microscope image of a quantum simulator made from a 1D array of Josephson junctions (light dots). (Courtesy: Philip Krantz, Krantz NanoArt, adapted by APS / Alan Stonebraker)

Topics: Modern Physics, Nanotechnology, Quantum Mechanics, Superconductors

A theory that describes how quantum particles interact with each other in 1D has been put to the test by two independent teams of physicists. In one experiment, aspects of the Tomonaga–Luttinger theory were verified using laser-trapped ultracold atoms. The other study made use of superconducting devices. Confirmation of the theory could lead to the development of new technologies based on nanowires and other 1D systems. Applications include electronics, sensing, energy harvesting and quantum information.

Tomonaga–Luttinger theory describes a 1D ensemble of interacting quantum particles in terms of a Tomonaga–Luttinger liquid (TLL). It predicts properties of 1D quantum systems such as how electrons behave in a nanowire. Testing these predictions in a systematic way has not been possible, however, because it is very difficult to control how particles interact in 1D systems such as nanowires.

Atoms and Josephson junctions simulate 1D quantum liquid, Hamish Johnston, Physics World

Atom by Atom...

Fig. 1 Experimental schematic of the hybrid system and ToF apparatus.

(A) A schematic of the experimental apparatus, including the LQT, the high voltage pulsing scheme (shown as solid and dashed lines), and the ToF. (B) An illustrative experimental time sequence that depicts initialization of a Ba+ crystal, production of BaOCH3+ (visualized as dark ions in the crystal) through reactions with methanol vapor, and subsequent MOT immersion. (C) Sample mass spectra obtained after ejecting the LQT species into the ToF after various MOT immersion times, ti, along with an inset depicting a superimposed fluorescence image of an ion crystal immersed in the Ca MOT. (D) Mass spectra of photofragmentation products collected after inducing photodissociation of BaOCa+. The identified photofragments were used to verify the elemental composition of the product.

Topics: Atomic Physics, Modern Physics, Nanotechnology, Quantum Mechanics

LA physicists have pioneered a method for creating a unique new molecule that could eventually have applications in medicine, food science and other fields. Their research, which also shows how chemical reactions can be studied on a microscopic scale using tools of physics, is reported in the journal Science.

For the past 200 years, scientists have developed rules to describe chemical reactions that they’ve observed, including reactions in food, vitamins, medications and living organisms. One of the most ubiquitous is the “octet rule,” which states that each atom in a molecule that is produced by a chemical reaction will have eight outer orbiting electrons. (Scientists have found exceptions to the rule, but those exceptions are rare.)

But the molecule created by UCLA professor Eric Hudson and colleagues violates that rule. Barium-oxygen-calcium, or BaOCa+, is the first molecule ever observed by scientists that is composed of an oxygen atom bonded to two different metal atoms.

Normally, one metal atom (either barium or calcium) can react with an oxygen atom to produce a stable molecule. However, when the UCLA scientists added a second metal atom to the mix, a new molecule, BaOCa+, which no longer satisfied the octet rule, had been formed. [1]

Abstract

Hypermetallic alkaline earth (M) oxides of formula MOM have been studied under plasma conditions that preclude insight into their formation mechanism. We present here the application of emerging techniques in ultracold physics to the synthesis of a mixed hypermetallic oxide, BaOCa+. These methods, augmented by high-level electronic structure calculations, permit detailed investigation of the bonding and structure, as well as the mechanism of its formation via the barrierless reaction of Ca (3PJ) with BaOCH3+. Further investigations of the reaction kinetics as a function of collision energy over the range 0.005 K to 30 K and of individual Ca fine-structure levels compare favorably with calculations based on long-range capture theory. [2]

1. In step toward ‘controlling chemistry,’ physicists create a new type of molecule, atom by atom, Stuart Wolpert, UCLA Newsroom
2. Synthesis of mixed hypermetallic oxide BaOCa+ from laser-cooled reagents in an atom-ion hybrid trap
Prateek Puri¹, Michael Mills¹, Christian Schneider¹, Ionel Simbotin², John A. Montgomery Jr.², Robin Côté², Arthur G. Suits³, Eric R. Hudson¹,*
1 Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA.
2 Department of Physics, University of Connecticut, Storrs, CT 06269, USA.
3 Department of Chemistry, University of Missouri, Columbia, MO 65211, USA.
*Corresponding author. Email: eric.hudson@ucla.edu

Nanoscale Quantum Memory...

Electron microscope image of the optical cavity used to make a quantum memory. Each segment in the cavity has a vertical dimension of about 690 nm (Courtesy: Tian Zhong et al / Science)

Topics: Modern Physics, Nanotechnology, Quantum Computer, Quantum Mechanics

A new type of optical quantum memory that could be integrated with other components on a chip has been unveiled by physicists in the US. The device overcomes an important challenge facing researchers trying to make quantum computers based on light – how to efficiently capture a photon within a sub-micron-sized structure.

From sending messages that could never be bugged to linking together quantum computers in a "quantum Internet", the ability to exchange quantum information may be vital to the future of technology. This will not be possible, however, without quantum memories to store quantum states and release them when needed.

In the Internet of today, information is sent between computers through a distributed series of nodes called routers. "Packets [of information] are maybe stored for some time and then they are sent," says Andrei Faraon of the California Institute of Technology, "There is some control over the timing of the packet." An optical network that uses photons to carry quantum information would require analogous nodes to store not strings of ones and zeroes (bits) but the full quantum states of individual photons (quantum bits or qubits).

There are currently several different quantum memories under development – some storing qubits as collective excitations in ensembles of atoms, others using solid-state crystals. Among the second group, crystals doped with ions of rare-earth metals have proved successful because rare-earth ions have sharp, stable electronic transitions that can couple to photons and preserve their quantum states. However, absorbing a photon generally requires millimetre- to centimetre-thicknesses of material, making quantum memories rather large.

Optical quantum memory shrinks to the nanoscale, Tim Wogan, Physics World

Quantum Engines and Entropy...

Image Source: Proceedings of the National Academy of Sciences 

Topics: Modern Physics, Quantum Mechanics, Thermodynamics

ABSTRACT

Two testable schemes for quantum heat engines are investigated under the quantization framework of noncommutative (NC) quantum mechanics (QM). By identifying the phenomenological connection between the phase-space NC driving parameters and an effective external magnetic field, the NC effects on the efficiency coefficient, N, of quantum engines can be quantified for two different cycles: an isomagnetic one and an isoenergetic one. In addition, paying a special attention to the quantum Carnot cycle, one notices that the inclusion of NC effects does not affect the maximal (Carnot) efficiency, N^C, ratifying the robustness of the second law of thermodynamics.

Quantum engines and the range of the second law of thermodynamics in the noncommutative phase-space
Jonas F. G. Santos, Alex E. Bernardini, Physics arXiv

Sisyphus Cooling...

Figure 1: Doyle and colleagues [2] have cooled SrOH molecules using Sisyphus cooling. In this type of cooling, the SrOH molecules are made to climb a potential energy hill, only to be transported back to the bottom, much like their Greek eponym who was doomed to roll a boulder up a hill over and over again. The energy lost in climbing the hill cools the SrOH molecules to ultracold temperatures. Show less

Topics: Bose-Einstein Condensate, Laser, Modern Physics, Nobel Prize, Quantum Mechanics

Only because of the illustration and the myth, but the process of laser cooling is quite sound, as the article describes below.

Physicists considering a foray into the study of molecules are often warned that “a diatomic molecule is one atom too many!” [1]. Now John Doyle and colleagues [2] at Harvard University have thrown this caution to the wind and tackled laser cooling of a triatomic molecule with success, opening the door to the study of ultracold polyatomic molecules.

The technique of laser cooling [3], which uses the scattering of laser photons and the concomitant momentum transfer to bring atoms to a near halt, has revolutionized atomic, molecular, and optical (AMO) physics. Laser cooling and an important variant known as Sisyphus cooling [4] underpin three Nobel prizes in physics—for magneto-optical trapping (1997), Bose-Einstein condensation (2001), and the manipulation of individual quantum systems (2012)—and are crucial to a host of quantum-assisted technologies and fundamental physics measurements.

Since photons carry very little momentum and therefore reduce an atom’s velocity by just a small amount, a prerequisite for effective laser cooling is the ability to scatter thousands of photons. Thus laser cooling has predominantly been used only to cool simple atoms, whose electronic structure dictates that after a photon is absorbed, spontaneous emission places the atomic electron back into its original state, allowing the process to repeat nearly ad infinitum.

Spurred on by the possibility of another revolution in AMO physics when ultracold molecules become available [5], a brave group of researchers recently began work to achieve laser cooling of diatomic molecules, guided by a new proposal for how to deal with their complex structure [6]. Diatomic molecules, or “diatoms,” are challenging targets for laser cooling as their electronic structure is complicated by their rotational and vibrational degrees of freedom. When a diatom absorbs a photon from the laser, spontaneous emission can place it in any of a multitude of these rotational and vibrational states, whose transition frequencies no longer match that of the cooling laser. These so-called dark states are the bane of laser cooling, bringing the cooling process to a stop. Nonetheless, by carefully choosing molecules with unique properties—for example, those which contain an optically active electron that does not strongly participate in the molecular bonding—laser cooling of molecules has been successful, and it has culminated in the demonstration of magneto-optical trapping of SrF molecules [7].

APS Viewpoint: A Diatomic Molecule is One Atom too Few
Paul Hamilton, Eric Hudson, University of California, Los Angeles

Qubits Entanglement...

This photograph of the quantum device has components highlighted in false colour. The superconducting qubits are numbered 1–10 and the central bus resonator is labelled "B". The red and blue structures are control lines for the individual qubits. (Courtesy: Chao Song et al/ arXiv: 1703.10302)

Topics: Entanglement, Modern Physics, Quantum Computer, Quantum Mechanics

A group of physicists in China has taken the lead in the race to couple together increasing numbers of superconducting qubits. The researchers have shown that they can entangle 10 qubits connected to one another via a central resonator – so beating the previous record by one qubit – and say that their result paves the way to quantum simulators that can calculate the behaviour of small molecules and other quantum-mechanical systems much more efficiently than even the most powerful conventional computers.

Superconducting circuits create qubits by superimposing two electrical currents, and hold the promise of being able to fabricate many qubits on a single chip through the exploitation of silicon-based manufacturing technology. In the latest work, a multi-institutional group led by Jian-Wei Pan of the University of Science and Technology of China in Hefei, built a circuit consisting of 10 qubits, each half a millimetre across and made from slivers of aluminium laid on to a sapphire substrate. The qubits, which act as non-linear LC oscillators, are arranged in a circle around a component known as a bus resonator.

Initially, the qubits are put into a superposition state of two oscillating currents with different amplitudes by supplying each of them with a very low-energy microwave pulse. To avoid interference at this stage, each qubit is set to a different oscillation frequency. However, for the qubits to interact with one another, they need to have the same frequency. This is where the bus comes in. It allows qubits to transfer energy from one another, but does not absorb any of that energy itself.

Physics World: Ten superconducting qubits entangled by physicists in China
Edwin Cartlidge