Dr. Peter Delfyett, Jr...

Dr. Peter Delfyett, Jr., National Society of Black Physicists

Topics: Diversity, Diversity in Science, Laser, Physics, Semiconductors

Dr. Peter Delfyett, former NSBP President and NSBP fellow, is the 2020 winner of the William Streifer Scientific Achievement Award. The William Streifer Scientific Achievement Award was established to recognize an exceptional single scientific contribution which has had a significant impact in the field of lasers and electro-optics in the past ten years. Dr. Delfyett has been selected, "For pioneering contributions to semiconductor diode based ultrafast laser science and technology." The Award is endowed by Xerox Corp and Spectra Diode Labs. The Award consists of an honorarium of $2,500 and a medal. The presentation is made at the IEEE Photonics Conference.

Learn more about this award and its previous winners.

Peter Delfyett wins the 2020 William Streifer Scientific Achievement Award, NSBP

#P4TC links:

Diaspora, 13 February 2012

Reducing the Impact of Negative Stereotypes on the Careers of Minority and Women Scientists, November 25, 2010

Entanglement...

Physicists take first-ever photo of quantum entanglement.
Credit: University of Glasgow/CC by 4.0

Topics: Einstein, Entanglement, Laser, Quantum Mechanics

Scientists just captured the first-ever photo of the phenomenon dubbed "spooky action at a distance" by Albert Einstein. That phenomenon, called quantum entanglement, describes a situation where particles can remain connected such that the physical properties of one will affect the other, no matter the distance (even miles) between them.

Einstein hated the idea, since it violated classical descriptions of the world. So he proposed one way that entanglement could coexist with classical physics — if there existed an unknown, "hidden" variable that acted as a messenger between the pair of entangled particles, keeping their fates entwined. [18 Times Quantum Particles Blew Our Minds in 2018]

There was just one problem: There was no way to test whether Einstein's view — or the stranger alternative, in which particles "communicate" faster than the speed of light and particles have no objective state until they are observed — was true. Finally, in the 1960s, physicist Sir John Bell came up with a test that disproves the existence of these hidden variables — which would mean that the quantum world is extremely weird.

This is "the pivotal test of quantum entanglement," said senior author Miles Padgett, who holds the Kelvin Chair of Natural Philosophy and is a professor of physics and astronomy at the University of Glasgow in Scotland. Though people have been using quantum entanglement and Bell's inequalities in applications such as quantum computing and cryptography, "this is the first time anyone has used a camera to confirm [it]."

To take the photo, Padgett and his team first had to entangle photons, or light particles, using a tried-and-true method. They hit a crystal with an ultraviolet (UV) laser, and some of those photons from the laser broke apart into two photons. "Due to conservation of both energy and momentum, each resulting pair [of] photons are entangled," Padgett said.

'Spooky' Quantum Entanglement Finally Captured in Stunning Photo
Yasemin Saplakoglu, Live Science

Ionic Clock...

Physics World: A brief history of timekeeping

Topics: Atomic Physics, Laser, NIST, Quantum Mechanics, Research

By confining single ions of aluminum and magnesium in an electric trap, cooling them to near absolute zero and probing them with laser beams, physicists at the National Institute of Standards and Technology (NIST) in Boulder, Colorado have built what is in effect the world’s most accurate clock. Having fractionally improved on the performance of another clock at NIST, the researchers have shown that their device would neither gain nor lose a second in 33 billion years (if it could run for that long). Such accurate timekeeping, they say, could boost geodesy and lead to new insights in fundamental physics.

The clocks that currently underpin atomic time rely on precisely measuring the frequency of microwaves emitted during a specific transition in cesium atoms. But such devices are limited by the relatively low frequency of that radiation. To keep time even more accurately, and eventually introduce a new definition of the second, physicists are developing clocks based on higher-frequency optical transitions.

The latest work at NIST features what is known as a quantum-logic clock. Built by Samuel Brewer and colleagues, it uses a positive ion of aluminum-27 as its timekeeper. When exposed to ultraviolet laser light at wavelength 267 nm, the ion undergoes a transition with a very narrow line width – making its frequency very well defined. What is more, that transition is largely immune to sources of external noise – such as blackbody radiation – that in other types of optical clock shift the frequency away from its true value.

A magnesium-25 ion is used to cool the aluminum down to the very low temperatures needed to minimize thermal noise. Cooling involves the absorption of photons at another specific frequency, but practical limitations mean that this cannot be done using the aluminum itself. This is because the required frequency in is too high for any practical laser. By entangling the two ions, the magnesium cools the aluminum via Coulomb interactions. This process also allows the quantum state of the aluminum ion to be read-out following exposure to the clock laser.

Entangled aluminum ion is world’s best timekeeper, Edwin Cartlidge, Physics World

3D Topological Insulators...

Courtesy: H. Chen

Topics: Laser, Optical Physics, Photonics, Materials Science, Nanotechnology, Quantum Mechanics

Reference: Topological Insulators, then the rest of the post.

Researchers in China and Singapore say they have made the first ever 3D photonic topological insulator using a stack of thin plastic sheets embedded with metal nanoantennas. The insulator works at microwave frequencies, but if extended to terahertz or optical wavelengths, it could find use in applications such as high-power lasers, optical diodes and photonic computer chips.

2D topological insulators, also known as 2D quantum spin Hall insulators, are materials that are electrical insulators in the bulk but can conduct electricity extremely well on their edge via special, topologically protected, electronic states. Electrons can only travel in one direction along these states and do not backscatter. This means that they can carry electrical current with near-zero dissipation of energy and so could be used to make energy-efficient electronic devices in the future.

Structures made from photonic crystals

In recent years, researchers have started looking at making topological insulators that work using light rather than electric currents. These structures are made from photonic crystals – materials in which the periodic variation of the refractive index means that only certain wavelengths of light are able to pass through. One of the advantages of these photonic topological insulators is that they can operate at room temperature, unlike their electronic counterparts.

Another is that the space through which photons can travel can be engineered so that it is curved like the surface of a cone. These structures thus mimic a 2D quantum spin Hall insulator that naturally contains so-called surface Dirac cones. These are the sharp single points in a 2D material at which the valence and the conduction bands meet at the Fermi level, and at which electrons behave as though they are relativistic particles with no rest mass.

3D topological insulators go photonic, Belle Dumé, Physics World

Hailing Frequencies Open...

On target: artist's impression of a laser beacon. (Courtesy: MIT News)

Topics: Astrobiology, Astrophysics, Laser, SETI, Space Exploration, Star Trek

A bright laser beacon that announces our presence to extraterrestrial civilizations could soon be achievable, new research suggests. Calculations done by James Clark and Kerri Cahoy at the Massachusetts Institute of Technology suggest that current and near-future technologies could be used to produce light intense enough to be detectable to extrasolar astronomers as distant as 20,000 light-years away. The duo’s research also sheds light on how we could detect signs of intelligent life in star systems beyond our own.

For decades, some in the astronomy community pondered what would be the best way of communicating with intelligent alien life on distant planets. Once a purely academic question, the desire to communicate has been heighten recently by the ongoing discovery of large numbers of exoplanets orbiting stars other than the Sun.

Recently, two nearby exoplanets have proved particularly attractive for such efforts. These are Proxima Centauri b, a planet which lies in the habitable zone of our closest star just 4 light-years away; and the TRAPPIST-1 system, which at a distance of 40 light-years is believed to contain three potentially habitable exoplanets, are currently viewed as our best hopes for receiving replies to our messages.

Megawatt laser beacon could communicate with aliens
James Clark and Kerri Cahoy, Physics World

Shrink Ray...

Using a new kind of "shrink ray", UT Austin scientists can alter the surface of a hydrogel pad in real time, creating grooves (blue) and other patterns without disturbing living cells, such as this fibroblast cell (red) that models the behavior of human skin cells. Rapid appearance of such surface features during cell growth can mimic the dynamic conditions experienced during development and repair of tissue (e.g., in wound healing and nerve regrowth). Credit: Jason Shear/University of Texas at Austin.

Topics: Biology, Chemistry, Laser, Research, Science Fiction

From "Fantastic Voyage" to "Despicable Me," shrink rays have been a science-fiction staple on screen. Now chemists at The University of Texas at Austin have developed a real shrink ray that can change the size and shape of a block of gel-like material while human or bacterial cells grow on it. This new tool holds promise for biomedical researchers, including those seeking to shed light on how to grow replacement tissues and organs for implants.

"To understand, and in the future engineer, the way that cells respond to the physical properties of their environment, you want to have materials that are dynamically re-shapeable," said Jason B. Shear, professor of chemistry and co-inventor of the new tool.

The work was published online today in the Journal of the American Chemical Society.

The real power of shrinking the material used to grow cells—called the substrate—isn't so much in making it smaller as it is in selectively changing the shape and texture of the surface. By controlling precisely which parts of the interior of the material shrink, the researchers can create specific 3-D features on the surface including bumps, grooves and rings. It's like pinching a rug from below to form peaks and valleys on the surface.

The researchers can also change the location and shapes of surface features as time goes by, for example turning a mountain into a molehill or even a sinkhole, mimicking the dynamic nature of the environment in which cells typically live, grow and move.

The shrink ray is a near-infrared laser that can be focused onto tiny points inside the substrate. The substrate looks and behaves a bit like a block of Jell-O. On the microscopic level, it's made of proteins jumbled and intertwined like a pile of yarn. When the laser strikes a point within the substrate, new chemical bonds are formed between the proteins, drawing them in more tightly, a change that also alters the surface shape as it's tugged on from below. Researchers scan the laser through a series of points within the substrate to create any desired surface contour at any place in relation to targeted cells.

Unlike other methods for altering the substrate under living cells, the UT Austin shrink ray doesn't heat or chemically alter the surface, damage living cells or cause cells to unstick from the surface. And it allows the formation of any 3-D pattern on demand while viewing the growing cells through a microscope.

Honey, I shrunk the cell culture, University of Texas at Austin

Tools Made of Light...

Topics: Diversity in Science, Optical Tweezers, Laser, Nobel Prize, Women in Science

I'm pretty sure I was in the throw of midterms. I did not miss it, just didn't have time to post about it.

Tools made of light

The inventions being honored this year have revolutionized laser physics. Extremely small objects and incredibly rapid processes are now being seen in a new light. Advanced precision instruments are opening up unexplored areas of research and a multitude of industrial and medical applications.

Arthur Ashkin invented optical tweezers that grab particles, atoms, viruses and other living cells with their laser beam fingers. This new tool allowed Ashkin to realise an old dream of science fiction – using the radiation pressure of light to move physical objects. He succeeded in getting laser light to push small particles towards the centre of the beam and to hold them there. Optical tweezers had been invented.

A major breakthrough came in 1987, when Ashkin used the tweezers to capture living bacteria without harming them. He immediately began studying biological systems and optical tweezers are now widely used to investigate the machinery of life.

Gérard Mourou and Donna Strickland paved the way towards the shortest and most intense laser pulses ever created by mankind. Their revolutionary article was published in 1985 and was the foundation of Strickland’s doctoral thesis.

Press release: The 2018 Nobel Prize in Physics. NobelPrize.org. Nobel Media AB 2018. Mon. 22 Oct 2018. < https://www.nobelprize.org/prizes/physics/2018/press-release/ >

ColdQuanta...

Lasers are used to trap arrays of atoms within glass chambers made by ColdQuanta, a neutral atom quantum computing startup. COLDQUANTA INC.

Topics: Computer Science, Laser, Quantum Computer, Quantum Mechanics

In a small basement laboratory, Harry Levine, a Harvard University graduate student in physics, can assemble a rudimentary computer in a fraction of a second. There isn't a processor chip in sight; his computer is powered by 51 rubidium atoms that reside in a glass cell the size of a matchbox. To create his computer, he lines up the atoms in single file, using a laser split into 51 beams. More lasers—six beams per atom—slow the atoms until they are nearly motionless. Then, with yet another set of lasers, he coaxes the atoms to interact with each other, and, in principle, perform calculations.

It's a quantum computer, which manipulates "qubits" that can encode zeroes and ones simultaneously in what's called a superposition state. If scaled up, it might vastly outperform conventional computers at certain tasks. But in the world of quantum computing, Levine's device is somewhat unusual. In the race to build a practical quantum device, investment has largely gone to qubits that can be built on silicon, such as tiny circuits of superconducting wire and small semiconductors structures known as quantum dots. Now, two recent studies have demonstrated the promise of the qubits Levine works with: neutral atoms. In one study, a group including Levine showed a quantum logic gate made of two neutral atoms could work with far fewer errors than ever before. And in another, researchers built 3D structures of carefully arranged atoms, showing that more qubits can be packed into a small space by taking advantage of the third dimension.

The advances, along with the arrival of venture capital funding, suggest neutral atoms could be on the upswing, says Dana Anderson, CEO of ColdQuanta, a Boulder, Colorado–based company that is developing an atom-based quantum computer. "We've done our homework," Anderson says. "This is really in the engineering arena now."

Arrays of atoms emerge as dark horse candidate to power quantum computers
Sophia Chen, Science Mag

Evidence of Things Unseen...

Schematic illustration of charge carriers confined within a TMD flake comprising different thicknesses. Charge carriers in the ground state (blue) can be excited upon resonant light excitation to a higher state (pink). Credit: ICFO/Fabien Vialla

Topics: Laser, Nanotechnology, Optical Physics, Quantum Mechanics, Semiconductor Technology

All deference to the Apostle Paul. It seemed an apropos title to the post.

Semiconducting heterostructures are key to the development of electronics and opto-electronics. Many applications in the infrared and terahertz frequency range exploit transitions, called intersubband transitions, between quantized states in semiconductor quantum wells. These intraband transitions exhibit very large oscillator strengths, close to unity. Their discovery in III-V semiconductor heterostructures depicted a huge impact within the condensed matter physics community and triggered the development of quantum well infrared photodetectors as well as quantum cascade lasers.

Quantum wells of the highest quality are typically fabricated by molecular beam epitaxy (sequential growth of crystalline layers), which is a well-established technique. However, it poses two major limitations: Lattice-matching is required, restricting the freedom in materials to choose from, and the thermal growth causes atomic diffusion and increases interface roughness.

2-D materials can overcome these limitations since they naturally form a quantum well with atomically sharp interfaces. They provide defect-free and atomically sharp interfaces, enabling the formation of ideal QWs, free of diffusive inhomogeneities. They do not require epitaxial growth on a matching substrate and can therefore be easily isolated and coupled to other electronic systems such as Si CMOS or optical systems such as cavities and waveguides.

Surprisingly enough, intersubband transitions in few-layer 2-D materials had never been studied before, neither experimentally nor theoretically. Thus, in a recent study published in Nature Nanotechnology, ICFO researchers Peter Schmidt, Fabien Vialla, Mathieu Massicotte, Klaas-Jan Tielrooij, Gabriele Navickaite, led by ICREA Prof at ICFO Frank Koppens, in collaboration with the Institut Lumière Matière—CNRS, Technical University of Denmark, Max Planck Institute for the Structure and Dynamics of Matter, CIC nanoGUNE, and the National Graphene Institute, report on the first theoretical calculations and first experimental observation of inter-sub-band transitions in quantum wells of few-layer semiconducting 2-D materials (TMDs).

Nano-imaging of intersubband transitions in few-layer 2-D materials, Phys dot org

More information: Peter Schmidt et al. Nano-imaging of intersubband transitions in van der Waals quantum wells, Nature Nanotechnology (2018). DOI: 10.1038/s41565-018-0233-9

58 Years to the Blue Ray...

Bright prospect: the first International Day of Light will be celebrated on 16 May. (Courtesy: iStock/RichLegg)

Topics: Applied Physics, Laser, Optical Physics, Photonics

This month sees the first International Day of Light. Wednesday 16 May was chosen because it is the anniversary of the first successful operation of the laser, as demonstrated by the American engineer and physicist Ted Maiman in 1960.

It’s a good choice, because the laser is a perfect example of how a scientific discovery can yield revolutionary benefits to society in all sorts of areas, including communications, healthcare and manufacturing. However, when I read the words “first successful operation of the laser” on the International Day of Light website (lightday.org), I had to look further, as it sounded like there might be more to the story.

I have spent most of my career working in photonics, optical communications and lighting, so I was already somewhat familiar with the laser’s history. However, the details still interested me. It turns out that although Maiman did indeed demonstrate the first working laser on 16 May 1960, he is not the only person with a reasonable claim to have “invented” the laser. The other is Gordon Gould, another US physicist who described “Some rough calculations on the feasibility of a LASER: Light Amplification by Stimulated Emission of Radiation” in his lab notebook in November 1957.

A day of light, James McKenzie, Physics World

Funnel Booster...

a) Schematic shows the band structure of the semiconducting HfS2/HfO2 when under strain, and the consequent charge funnelling. b) The strain is induced in the semiconductor by creating a region of oxide using intense laser light. c) A photocurrent map of the device; the photoresponse drastically increases when a region (dashed circle, bottom) is oxidized, compared with the same device before oxidation (top), a sign of the charge funnelling effect. Figure reproduced with permission from the authors and Nature Communications.

Topics: Green Energy, Green Tech, Laser, Nanotechnology, Semiconductor Technology, Solar Power

Note: Radiant solar energy = 1.1 x 10¹⁸ kilowatt hours/year; 3.013 x 10¹⁵ kilowatt hours/day. We're literally "leaving money on the table"... for fossil fuel greed.

Source: United Nations World Energy Assessment: Energy and the Challenge of Sustainability

Funnels are efficient tools for channelling liquids into containers with narrow openings. Now, researchers in Exeter have demonstrated the first funnel for electrical charges on a chip. The discovery builds on the ability to oxidize the atomically thin semiconductor, hafnium disulphide (HfS2), with a high-intensity UV laser. The non-uniform strain between oxidized and non-oxidized regions, and the subsequent band-gap modulation, generates electric fields, which effectively funnel the charges in the semiconductor flakes to areas where they can be more easily collected. This concept could enable a new generation of solar cells with 60% efficiency (currently around 21%), thanks to the increased efficiency in collecting photo-excited charges and the potential for hot-carrier extraction.

Intense laser light means oxidation, oxidation means strain

In general, bulk semiconductors can only sustain strains up to 0.4% before breaking. However, a layer of semiconductor that is only a few atoms thick can support strains of up to 25%. This amount of strain changes the band gap in the energy dispersion by up to 1 eV. In this work, Saverio Russo and his group at the University of Exeter, induce the strain in the HfS2 using a 375 nm laser to remove sulphur atoms, which are then replaced by oxygen atoms. According to calculations performed using density functional theory, the hafnium atoms have different separations in HfS2 and HfO2. This produces a 2.7% strain at the boundary between the oxidized and non-oxidized regions. Electrical contacts anchor the material to a substrate, so a strain gradient is present across the whole flake, shifting asymmetrically the conduction and valence bands to higher energies, and opening the band gap by 30 meV.

Funneling charges to boost solar-cell efficiency, Lauren Barr, PhD, network contributor for nanotechweb.org

One out of Two...

Collision course: two atoms held in optical tweezers before forming a molecule
(Courtesy: Lee Liu and Yu Liu)

Topics: Chemistry, Laser, Optical Physics, Optical Tweezers, Particle Physics

A single molecule has been created by combining individual atoms of sodium and caesium, using optical tweezers to guide them into place. The technique, devised by Lee Liu and colleagues at Harvard University and Harvard-MIT Health Sciences and Technology, could help chemists to study chemical reactions far more precisely by giving them control over the individual atomic and molecular collisions. The team hopes that their method will be used in a variety of fields to create diverse, complex molecules, allowing for discoveries of previously unforeseen molecular properties.

Conventional studies of chemical reactions involve observing the macroscopic results of large numbers of collisions of atoms and molecules – rather than studying individual collisions. Currently, chemists need to compare experimental reaction rates with theoretical models to calculate the probabilities of individual collisions taking place – a process that is fundamental to the understanding of chemistry. An alternative, and more precise, technique is to study interactions between individual atoms and molecules – something that requires great experimental dexterity.

To begin their interaction process, Liu and colleagues use magneto-optical traps to prepare reservoirs of stationary atoms of sodium and caesium at just a few hundred microkelvin. “Cooling and controlling atoms and molecules to temperatures where they are standing still allows for easier manipulations of their properties, interactions and reactions,” explains team leader Kang-Kuen Ni.

Optical tweezers create a single molecule from two atoms, Sam Jarman, Physics World

Nanowire Fusion...

The target chamber used to achieve laser fusion is shown in the foreground and the laser appears in the background. (Courtesy: Advanced Beam Laboratory/Colorado State University)

Topics: Green Tech, Nanotechnology, Nuclear Fusion

Smaller, cheaper neutron sources and new opportunities for simulating the extreme conditions at the center of stars are among the possible benefits of new research carried out by physicists in the US and Germany. The group directed rapid-fire pulses of intense blue light from a compact laser at arrays of nanostructures to generate a dense plasma yielding large numbers of neutrons created by nuclear fusion.

Scientists have built ever more energetic lasers in the quest to demonstrate nuclear fusion’s feasibility as an energy source. The National Ignition Facility (NIF) in California, for example, generates pulses with a whopping 1.8 MJ of energy, in order to compress tiny pellets of deuterium and tritium to the point where the nuclei fuse and emit copious numbers of neutrons. The aim is to achieve ignition, when the alpha particle released by the fusing nuclei provides the heat for a self-sustaining reaction – with the energy of the emitted neutrons ultimately being tapped to produce electricity. However, NIF is enormous – occupying the area of three football pitches – and, like other high-energy lasers, can only fire a handful of times a day.

Some researchers are instead working on less energetic but more rapid-fire lasers. These will never get anywhere close to ignition, but can still achieve exceptionally high intensities – thanks to the extreme brevity and hence power of their pulses. Such lasers can create plasmas with very high energy densities ideal for studying extreme astrophysical environments, for example. These devices could also potentially be used as compact sources of neutrons, which probe atomic structure in ways not possible with X-rays. Neutrons are usually produced at large accelerators or reactors and a compact source would be welcomed by scientists.

Nanowires boost nuclear fusion, Hamish Johnston, Physics World

Laser Phone Charging...

A new laser system can wirelessly recharge phones from across the room(Credit: Mark Stone/University of Washington)

Topics: Applied Physics, Electrical Engineering, Electronics, Laser

We've cut the cord for communication, thanks to Bluetooth and Wi-Fi, but charging our little pocket supercomputers still takes a tether. Judging by the range of wireless charging technologies in the works, that might not be the case for much longer. A team from the University of Washington has demonstrated how lasers could be used to charge a device from across the room.

The team mounted a power cell on the back of a smartphone and hit it with a narrow laser beam in the near-infrared part of the spectrum. From a distance of 4.3 m (14 ft), the laser was able to deliver 2 W of power to a 97-sq cm (15-sq in) area, charging the phone about as quickly as a regular old USB cable.

The laser emitter is designed to automatically sense when a phone is ready to be charged, while the smartphone was programmed to send out high-frequency "chirps" inaudible to the human ear that tells the emitter where it is.

"This acoustic localization system ensures that the emitter can detect when a user has set the smartphone on the charging surface, which can be an ordinary location like a table across the room," says Vikram Iyer, co-author on a study describing the device.

Laser system wirelessly charges phones from across the room, Michael Irving, New Atlas

Laser Fusion...

Credit: ORNL

Topics: Green Energy, Green Tech, Lasers, Nuclear Fusion, Nuclear Physics

A laser-driven technique for creating fusion that dispenses with the need for radioactive fuel elements and leaves no toxic radioactive waste is now within reach, say researchers.

Dramatic advances in powerful, high-intensity lasers are making it viable for scientists to pursue what was once thought impossible: creating fusion energy based on hydrogen-boron reactions. And an Australian physicist is in the lead, armed with a patented design and working with international collaborators on the remaining scientific challenges.

In a paper in the scientific journal Laser and Particle Beams today, lead author Heinrich Hora from the University of New South Wales in Sydney and international colleagues argue that the path to hydrogen-boron fusion is now viable, and may be closer to realization than other approaches, such as the deuterium-tritium fusion approach being pursued by U.S. National Ignition Facility (NIF) and the International Thermonuclear Experimental Reactor under construction in France.

"I think this puts our approach ahead of all other fusion energy technologies," said Hora, who predicted in the 1970s that fusing hydrogen and boron might be possible without the need for thermal equilibrium. Rather than heat fuel to the temperature of the Sun using massive, high-strength magnets to control superhot plasmas inside a doughnut-shaped toroidal chamber (as in ITER), hydrogen-boron fusion is achieved using two powerful lasers in rapid bursts, which apply precise non-linear forces to compress the nuclei together.

Laser-driven technique for creating fusion is now within reach, say researchers
More information: H. Hora et al, Road map to clean energy using laser beam ignition of boron-hydrogen fusion, Laser and Particle Beams (2017).
DOI: 10.1017/S0263034617000799

FAST Entanglement...

While quantum entanglement usually spreads through the atoms in an optical lattice via short-range interactions with the atoms' immediate neighbors (left), new theoretical research shows that taking advantage of long-range dipolar interactions among the atoms could enable it to spread more quickly (right), a potential advantage for quantum computing and sensing applications.
Credit: Gorshkov and Hanacek/NIST

Topics: Laser, Materials Science, Optical Physics, Quantum Mechanics

“It is these long-range dipolar interactions in 3-D that enable you to create entanglement much faster than in systems with short-range interactions,” said Gorshkov, a theoretical physicist at NIST and at both the Joint Center for Quantum Information and Computer Science and the Joint Quantum Institute, which are collaborations between NIST and the University of Maryland. “Obviously, if you can throw stuff directly at people who are far away, you can spread the objects faster.”

Applying the technique would center around adjusting the timing of laser light pulses, turning the lasers on and off in particular patterns and rhythms to quick-change the suspended atoms into a coherent entangled system.

The approach also could find application in sensors, which might exploit entanglement to achieve far greater sensitivity than classical systems can. While entanglement-enhanced quantum sensing is a young field, it might allow for high-resolution scanning of tiny objects, such as distinguishing slight temperature differences among parts of an individual living cell or performing magnetic imaging of its interior.

Gorshkov said the method builds on two studies from the 1990s in which different NIST researchers considered the possibility of using a large number of tiny objects—such as a group of atom—as sensors. Atoms could measure the properties of a nearby magnetic field, for example, because the field would change their electrons’ energy levels. These earlier efforts showed that the uncertainty in these measurements would be advantageously lower if the atoms were all entangled, rather than merely a bunch of independent objects that happened to be near one another.

Need Entangled Atoms? Get 'Em FAST! With NIST’s New Patent-Pending Method

Paper: Z. Eldredge, Z.-X. Gong, J. T. Young, A.H. Moosavian, M. Foss-Feig and A.V. Gorshkov. Fast State Transfer and Entanglement Renormalization Using Long-Range Interactions. Physical Review Letters. Published 25 October 2017. DOI: 10.1103/PhysRevLett.119.170503

Quantum Light on a Chip...

A laser (green) excites the quantum dot (red) in this diagram of the chip. The ring, which is tuned via applying voltage to the yellow contacts, manipulates the characteristics of individual photons (ellipsoids).

Topics: Laser, Nanotechnology, Photonics, Quantum Dots, Quantum Mechanics, Solid State Physics

Ideally, optical circuits would generate and shuttle light so well that researchers could use them to transmit encoded information, sense chemical species, and perform quantum computations. But because the components for each circuit—light sources, mirrors, splitters, filters, and waveguides—occupy several feet of table space, they cannot manipulate light down to the nanoscale. In an effort to downsize components and produce practical quantum photonic devices, researchers have been tinkering with nonlinear materials, atomic defects, and traditional semiconductors at the nanoscale.

Now Ali Elshaari at KTH Stockholm and his colleagues have taken a major stride by embedding circuit components on a CMOS-compatible chip that takes up a millionth the area of a tabletop apparatus. The key innovation was implementing precise control over quantum dot light sources, which emit photons in specific quantum states, including entangled ones, when excited by lasers. Scientists had struggled to control the dots’ emission and integrate the dots with waveguides for on-chip applications. Elshaari’s team devised a special geometry that optimized the alignment of the dots’ light emission with the fundamental waveguide mode, which resulted in high coupling efficiencies. To control the emission, an electrically tunable device acted as a spectral filter that could fine-tune the photon characteristics.

Manipulating quantum light on a chip, Katyayani Seal, Physics Today

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

Lasers and Anti-Lasers...

Schematics above show light input (green) entering opposite ends of a single device. When the phase of light input 1 is faster than that of input 2 (left panel), the gain medium dominates, resulting in coherent amplification of the light, or a lasing mode. When the phase of light input 1 is slower than input 2 (right panel), the loss medium dominates, leading to coherent absorption of the input light beams, or an anti-lasing mode. Credit: Zi Jing Wong/UC Berkeley

Topics: Laser, Modern Physics, Optical Physics

Bringing opposing forces together in one place is as challenging as you would imagine it to be, but researchers in the field of optical science have done just that.

Scientists at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) have for the first time created a single device that acts as both a laser and an anti-laser, and they demonstrated these two opposite functions at a frequency within the telecommunications band.

Their findings, reported in a paper to be published Monday, Nov. 7, in the journal Nature Photonics, lay the groundwork for developing a new type of integrated device with the flexibility to operate as a laser, an amplifier, a modulator, and an absorber or detector.

"In a single optical cavity we achieved both coherent light amplification and absorption at the same frequency, a counterintuitive phenomenon because these two states fundamentally contradict each other," said study principal investigator Xiang Zhang, senior faculty scientist at Berkeley Lab's Materials Sciences Division. "This is important for high-speed modulation of light pulses in optical communication."

Phys.org:
Lasers + anti-lasers: Marriage opens door to development of single device with exceptional range of optical capabilities

Laser Plasma...

Simulation of a laser pulse that's created a plasma aperture in a thin foil. (Courtesy: Bruno Gonzalez-Izquierdo et al/Nature Communications)

Topics: Laser, Optical Physics, Plasma Physics, Research

The quality of laser-accelerated proton beams can be improved by controlling the polarization of the incident laser light, researchers in the UK have discovered. The finding could help physicists to create compact sources of proton beams for use in medicine, lithography or even astrophysics.

Beams of protons and other positive ions have a wide range of applications, including particle physics, materials processing and medicine. Proton-beam therapy, for example, is used to destroy some cancerous tumours with a minimum of collateral damage to surrounding healthy tissue. However, the practical use of proton and ion beams is held back by the need for large and expensive particle accelerators to generate high-quality beams.

One way forward is laser-plasma acceleration, in which a high-power laser pulse is fired into a target. This creates a plasma in which the electrons separate from the ions. This creates huge electric fields that are capable of accelerating protons, ions and electrons to very high energies.

Physics World: Laser polarization boosts quality of proton beams, Tim Wogan