Laser-like photons signal major step towards quantum 'Internet'

It is an artist's impression of distributed qubits (the bright spots) linked to each other via photons (the light beams). The colors of the beams represent that the optical frequency of the photons in each link can be tailored to the needs of the network.

The realization of quantum networks is one of the major challenges of modern physics. Now, new research shows how high-quality photons can be generated from 'solid-state' chips, bringing us closer to the quantum 'internet'.   The number of transistors on a microprocessor continues to double every two years, amazingly holding firm to a prediction by Intel co-founder Gordon Moore almost 50 years ago.   If this is to continue, conceptual and technical advances harnessing the power of quantum mechanics in microchips will need to be investigated within the next decade. Developing a distributed quantum network is one promising direction pursued by many researchers today.   A variety of solid-state systems are currently being investigated as candidates for quantum bits of information, or qubits, as well as a number of approaches to quantum computing protocols, and the race is on for identifying the best combination. One such qubit, a quantum dot, is made of semiconductor nanocrystals embedded in a chip and can be controlled electro-optically.   Single photons will form an integral part of distributed quantum networks as flying qubits. First, they are the natural choice for quantum communication, as they carry information quickly and reliably across long distances. Second, they can take part in quantum logic operations, provided all the photons taking part are identical.   Unfortunately, the quality of photons generated from solid-state qubits, including quantum dots, can be low due to decoherence mechanisms within the materials. With each emitted photon being distinct from the others, developing a quantum photonic network faces a major roadblock.   Now, researchers from the Cavendish Laboratory at Cambridge University have implemented a novel technique to generate single photons with tailored properties from solid-state devices that are identical in quality to lasers. Their research is published today in the journal Nature Communications.   As their photon source, the researchers built a semiconductor Schottky diode device containing individually addressable quantum dots. The transitions of quantum dots were used to generate single photons via resonance fluorescence – a technique demonstrated previously by the same team.   Under weak excitation, also known as the Heitler regime, the main contribution to photon generation is through elastic scattering. By operating in this way, photon decoherence can be avoided altogether. The researchers were able to quantify how similar these photons are to lasers in terms of coherence and waveform – it turned out they were identical.   "Our research has added the concepts of coherent photon shaping and generation to the toolbox of solid-state quantum photonics," said Dr Mete Atature from the Department of Physics, who led the research.   "We are now achieving a high-rate of single photons which are identical in quality to lasers with the further advantage of coherently programmable waveform - a significant paradigm shift to the conventional single photon generation via spontaneous decay."   There are already protocols proposed for quantum computing and communication which rely on this photon generation scheme, and this work can be extended to other single photon sources as well, such as single molecules, colour centres in diamond and nanowires.   "We are at the dawn of quantum-enabled technologies, and quantum computing is one of many thrilling possibilities," added Atature.   "Our results in particular suggest that multiple distant qubits in a distributed quantum network can share a highly coherent and programmable photonic interconnect that is liberated from the detrimental properties of the chips. Consequently, the ability to generate quantum entanglement and perform quantum teleportation between distant quantum-dot spin qubits with very high fidelity is now only a matter of time."

Record simulations conducted on Lawrence Livermore supercomputer

Researchers at Lawrence Livermore National Laboratory have performed record simulations using all 1,572,864 cores of Sequoia, the largest supercomputer in the world. Sequoia, based on IBM BlueGene/Q architecture, is the first machine to exceed one million computational cores. It also is No. 2 on the list of the world's fastest supercomputers, operating at 16.3 petaflops (16.3 quadrillion floating point operations per second).

 

The simulations are the largest particle-in-cell (PIC) code simulations by number of cores ever performed. PIC simulations are used extensively in plasma physics to model the motion of the charged particles, and the electromagnetic interactions between them, that make up ionized matter. High performance computers such as Sequoia enable these codes to follow the simultaneous evolution of tens of billions to trillions of individual particles in highly complex systems.

 

Frederico Fiuza, a physicist and Lawrence Fellow at LLNL, performed the simulations in order to study the interaction of ultra-powerful lasers with dense plasmas in a proposed method to produce fusion energy, the energy source that powers the sun, in a laboratory setting. The method, known as fast ignition, uses lasers capable of delivering more than a petawatt of power (a million billion watts) in a fraction of a billionth of a second to heat compressed deuterium and tritium (DT) fuel to temperatures exceeding the 50 million degrees Celsius needed to initiate fusion reactions and release net energy. The project is part of the U.S. Department of Energy's Office of Fusion Energy Science Program.

 

This method differs from the approach being taken by LLNL's National Ignition Facility to achieve thermonuclear ignition and burn. NIF's approach is called the "central hot spot" scenario, which relies on simultaneous compression and ignition of a spherical fuel capsule in an implosion, much like in a diesel engine. Fast ignition uses the same hardware as the hot spot approach but adds a high-intensity, ultrashort-pulse laser as the "spark" that achieves ignition.

 

The code used in these simulations was OSIRIS, a PIC code that has been developed over more than 10 years in collaboration between the University of California, Los Angeles and Portugal's Instituto Superior Técnico. Using this code, Fiuza demonstrated excellent scaling in parallel performance of OSIRIS to the full 1.6 million cores of Sequoia. By increasing the number of cores for a relatively small problem of fixed size, what computer scientists call "strong scaling," OSIRIS obtained 75 percent efficiency on the full machine. But when the total problem size was increased, what is called "weak scaling," a 97 percent efficiency was achieved.

 

"This means that a simulation that would take an entire year to perform on a medium-size cluster of 4,000 cores can be performed in a single day. Alternatively, problems 400 times greater in size can be simulated in the same amount of time," Fiuza said. "The combination of this unique supercomputer and this highly efficient and scalable code is allowing for transformative research."

 

OSIRIS is routinely used for fundamental science during the test phase of Sequoia in simulations with up to 256,000 cores. These simulations are allowing researchers, for the first time, to model the interaction of realistic fast-ignition-scale lasers with dense plasmas in three dimensions with sufficient speed to explore a large parameter space and optimize the design for ignition. Each simulation evolves the dynamics of more than 100 billion particles for more than 100,000 computational time steps. This is approximately an order of magnitude larger than the previous largest simulations of fast ignition.

 

Sequoia is a National Nuclear Security Administration (NNSA) machine, developed and fielded as part of NNSA's Advanced Simulation and Computing (ASC) program. Sequoia is in preparations to move to classified computing in support of stockpile stewardship.

 

"This historic calculation is an impressive demonstration of the power of high-performance computing to advance our scientific understanding of complex systems," said Bill Goldstein, LLNL's deputy director for Science and Technology. "With simulations like this, we can help transform the outlook for laboratory fusion as a tool for science, energy and stewardship of the nuclear stockpile."

Fantastic flash memory combines graphene, molybdenite

EPFL scientists have combined two materials with advantageous electronic properties -- graphene and molybdenite -- into a flash memory prototype that is promising in terms of performance, size, flexibility and energy consumption.

EPFL scientists have combined two materials with advantageous electronic properties -- graphene and molybdenite -- into a flash memory prototype that is very promising in terms of performance, size, flexibility and energy consumption.   After the molybdenite chip, we now have molybdenite flash memory, a significant step forward in the use of this new material in electronics applications. The news is even more impressive because scientists from EPFL's Laboratory of Nanometer Electronics and Structures (LANES) came up with a truly original idea: they combined the advantages of this semiconducting material with those of another amazing material – graphene. The results of their research have recently been published in the journal ACS Nano.   Two years ago, the LANES team revealed the promising electronic properties of molybdenite (MoS2), a mineral that is very abundant in nature. Several months later, they demonstrated the possibility of building an efficient molybdenite chip. Today, they've gone further still by using it to develop a flash memory prototype – that is, a cell that can not only store data but also maintain it in the absence of electricity. This is the kind of memory used in digital devices such as cameras, phones, laptop computers, printers, and USB keys.   An ideal "energy band"   "For our memory model, we combined the unique electronic properties of MoS2 with graphene's amazing conductivity," explains Andras Kis, author of the study and director of LANES.   Molybdenite and graphene have many things in common. Both are expected to surpass the physical limitations of our current silicon chips and electronic transistors. Their two-dimensional chemical structure – the fact that they're made up of a layer only a single atom thick – gives them huge potential for miniaturization and mechanical flexibility.   Although graphene is a better conductor, molybdenite has advantageous semi-conducting properties. MoS2 has an ideal "energy band" in its electronic structure that graphene does not. This allows it to switch very easily from an "on" to an "off" state, and thus to use less electricity. Used together, the two materials can thus combine their unique advantages.   Like a sandwich   The transistor prototype developed by LANES was designed using "field effect" geometry, a bit like a sandwich. In the middle, instead of silicon, a thin layer of MoS2 channels electrons. Underneath, the electrodes transmitting electricity to the MoS2 layer are made out of graphene. And on top, the scientists also included an element made up of several layers of graphene; this captures electric charge and thus stores memory.   "Combining these two materials enabled us to make great progress in miniaturization, and also using these transistors we can make flexible nanoelectronic devices," explains Kis. The prototype stores a bit of memory, just a like a traditional cell. But according to the scientist, because molybdenite is thinner than silicon and thus more sensitive to charge, it offers great potential for more efficient data storage.

Autodesk sponsors international electric vehicle competition

Autodesk will be the primary sponsor of Purdue University's third International Collegiate evGrandPrix to be held on May 12, opening day weekend at the Indianapolis Motor Speedway, home of the Indianapolis 500.

The event is an electric go-kart race and engineering design competition involving colleges and universities from around the nation and Europe.

"In sponsoring the evGrandPrix, Autodesk is taking a leadership role in educating the next generation of engineers and technical specialists," said James Caruthers, Reilly Professor of Chemical Engineering and director of the Indiana Advanced Electric Vehicle Training and Education Consortium (I-AEVtec). "The evGrandPrix is not just a go-kart race, but it is really an engineering design competition where the students get points from race placement plus their engineering design, energy efficiency and also community outreach."

Autodesk, a lead sponsor of the evGrandPrix, is providing licenses of Autodesk design and simulation products to all student participants - design and simulation tools that they can use in the competition as well as throughout their tenure at Purdue and the other colleges and universities that are participating in the evGrandPrix.

"Thanks to Autodesk, our students are now using those high-end design tools as part of their education," Caruthers said. "This is a very generous contribution, and one that will go a long way toward preparing our students with the advanced technical skills they'll need to compete for the best engineering jobs when they graduate."

Autodesk also is helping to promote the event across the nation and the world to millions of students who are members of the Autodesk Education Community.

Team members will be able to simulate their go-kart designs with Autodesk's cloud-based services.

"Students can create, visualize, analyze, simulate, and iterate their designs faster and more efficiently by performing computationally intensive simulation tasks in the cloud," said Thom Tremblay, industry manager at Autodesk. "With Autodesk Simulation 360 students can test multiple 'what if' design scenarios in parallel."

Specialized tools from Autodesk help engineers simulate fatigue, stress and cracking, which can help identify areas of potential instability or damage. Participating students are able to access the engineering and design software from the Autodesk Education Community. The site also hosts a variety of learning tools to help foster a stronger fundamental understanding of engineering and sustainable design principles.

"One dimension of the evGrandPrix is a focus on sustainable design," Tremblay said. "Our Autodesk Sustainability Workshop offers online resources that teach the principles and practice of sustainability in engineering and design."

This will be the third year that the Collegiate evGrandPrix has been held at the Indianapolis Motor Speedway.

"The Indianapolis Motor Speedway was founded over 100 years ago to give automotive designers the ultimate facility to test new innovations and help advance vehicle technologies," said Jarrod Krisiloff, senior director of marketing at the Indianapolis Motor Speedway. "In many ways, the evGrandPrix is a continuation of the original mission of the track and we are pleased to host this competition at the Indianapolis Motor Speedway. The evGrandPrix not only showcases the engineering and design experience that these students offer future employers, but it also exposes the students to real-life examples of how they can apply their learning in the automotive and associated technology industries, including IndyCar racing." 

More information on the Collegiate evGrandPrix can be found at http://www.evgrandprix.org