Schroedinger

Since Erwin Schroedinger's famous 1935 cat thought experiment, physicists around the globe have tried to create large scale systems to test how the rules of quantum mechanics apply to everyday objects.

Researchers at the University of Calgary recently made a significant step forward in this direction by creating a large system that is in two substantially different states at the same time. Until this point, scientists had only managed to recreate quantum effects on much smaller scales.

Professor Alex Lvovsky and associate professor Christoph Simon from the Physics and Astronomy department together with their graduate students revealed their findings in a world leading physics research journal, Nature Physics.

Understanding Schroedinger's cat

In contrast to our everyday experience, quantum physics allows for particles to be in two states at the same time -- so-called quantum superpositions. A radioactive nucleus, for example, can simultaneously be in a decayed and non-decayed state.

Applying these quantum rules to large objects leads to paradoxical and even bizarre consequences. To emphasize this, Erwin Schroedinger, one of the founding fathers of quantum physics, proposed in 1935 a thought experiment involving a cat that could be killed by a mechanism triggered by the decay of a single atomic nucleus. If the nucleus is in a superposition of decayed and non-decayed states, and if quantum physics applies to large objects, the belief is that the cat will be simultaneously dead and alive.

While quantum systems with properties akin to 'Schroedinger's cat' have been achieved at a micro level, the application of this principle to everyday macro objects has proved to be difficult to demonstrate.

"This is because large quantum objects are extremely fragile and tend to disintegrate when subjected to any interaction with the environment," explains Lvovsky.

Photons help to illuminate the paradox

The breakthrough achieved by Calgary quantum physicists is that they were able to contrive a quantum state of light that consists of a hundred million light quanta (photons) and can even be seen by the naked eye. In their state, the "dead" and "alive" components of the "cat" correspond to quantum states that differ by tens of thousands of photons.

"The laws of quantum mechanics which govern the microscopic world are very different from classical physics that rules over large objects such as live beings," explains lead author Lvovsky. "The challenge is to understand where to draw the line and explore whether such a line exists at all. Those are the questions our experiment sheds light on," he states.

While the findings are promising, study co-author Simon admits that many questions remain unanswered.

"We are still very far from being able to do this with a real cat," he says. "But this result suggests there is ample opportunity for progress in that direction.
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Graphics Innovations

Research presented in a paper by Morgan McGuire, assistant professor of computer science at Williams College, and co-author Dr. David Luebke of NVIDIA, introduces a new algorithm to improve computer graphics for video games.

McGuire and Luebke have developed a new method for computerizing lighting and light sources that will allow video game graphics to approach film quality.

Their paper "Hardware-Accelerated Global Illumination by Image Space Photon Mapping" won a Best Paper award at the 2009 Conference on High Performance Graphics.

Because video games must compute images more quickly than movies, video game developers have struggled with maximizing graphic quality.

Producing light effects involves essentially pushing light into the 3D world and pulling it back to the pixels of the final image. The method created by McGuire and Luebke reverses the process so that light is pulled onto the world and pushed into the image, which is a faster process.

As video games continue to increase the degree of interactivity, graphics processors are expected to become 500 times faster than they are now. McGuire and Luebke's algorithm is well suited to the quickened processing speed, and is expected to be featured in video games within the next two years.

McGuire is author of "Creating Games: Mechanics, Content, and Technology" and is co-chair of the ACM SIGGRAPH Symposium on Non-Photorealistic Animation and Rendering, and previously chaired the ACM Symposium on Interactive 3D Graphics and Games.

He has worked on and consulted for commercial video games such as "Marvel Ultimate Alliance" (2009), "Titan Quest" (2006), and "ROBLOX" (2005).

McGuire received his B.S. from the Massachusetts Institute of Technology in 2000 and his Ph.D. from Brown University in 2006. At Williams since 2006, he teaches courses on computer graphics and game design
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Cloud Computing

Researchers have succeeded in combining the power of quantum computing with the security of quantum cryptography and have shown that perfectly secure cloud computing can be achieved using the principles of quantum mechanics. They have performed an experimental demonstration of quantum computation in which the input, the data processing, and the output remain unknown to the quantum computer.

The international team of scientists will publish the results of the experiment, carried out at the Vienna Center for Quantum Science and Technology (VCQ) at the University of Vienna and the Institute for Quantum Optics and Quantum Information (IQOQI), in the forthcoming issue of Science.

Quantum computers are expected to play an important role in future information processing since they can outperform classical computers at many tasks. Considering the challenges inherent in building quantum devices, it is conceivable that future quantum computing capabilities will exist only in a few specialized facilities around the world -- much like today's supercomputers. Users would then interact with those specialized facilities in order to outsource their quantum computations. The scenario follows the current trend of cloud computing: central remote servers are used to store and process data -- everything is done in the "cloud." The obvious challenge is to make globalized computing safe and ensure that users' data stays private.

The latest research, to appear in Science, reveals that quantum computers can provide an answer to that challenge. "Quantum physics solves one of the key challenges in distributed computing. It can preserve data privacy when users interact with remote computing centers," says Stefanie Barz, lead author of the study. This newly established fundamental advantage of quantum computers enables the delegation of a quantum computation from a user who does not hold any quantum computational power to a quantum server, while guaranteeing that the user's data remain perfectly private. The quantum server performs calculations, but has no means to find out what it is doing -- a functionality not known to be achievable in the classical world.

The scientists in the Vienna research group have demonstrated the concept of "blind quantum computing" in an experiment: they performed the first known quantum computation during which the user's data stayed perfectly encrypted. The experimental demonstration uses photons, or "light particles" to encode the data. Photonic systems are well-suited to the task because quantum computation operations can be performed on them, and they can be transmitted over long distances.

The process works in the following manner. The user prepares qubits -- the fundamental units of quantum computers -- in a state known only to himself and sends these qubits to the quantum computer. The quantum computer entangles the qubits according to a standard scheme. The actual computation is measurement-based: the processing of quantum information is implemented by simple measurements on qubits. The user tailors measurement instructions to the particular state of each qubit and sends them to the quantum server. Finally, the results of the computation are sent back to the user who can interpret and utilize the results of the computation. Even if the quantum computer or an eavesdropper tries to read the qubits, they gain no useful information, without knowing the initial state; they are "blind."

The research at the Vienna Center for Quantum Science and Technology (VCQ) at the University of Vienna and at the Institute for Quantum Optics and Quantum Information (IQOQI) of the Austrian Academy of Sciences was undertaken in collaboration with the scientists who originally invented the protocol, based at the University of Edinburgh, the Institute for Quantum Computing (University of Waterloo), the Centre for Quantum Technologies (National University of Singapore), and University College Dublin
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Batteries

Looking toward improved batteries for charging electric cars and storing energy from renewable but intermittent solar and wind, scientists at Oak Ridge National Laboratory have developed the first high-performance, nanostructured solid electrolyte for more energy-dense lithium ion batteries.

Today's lithium-ion batteries rely on a liquid electrolyte, the material that conducts ions between the negatively charged anode and positive cathode. But liquid electrolytes often entail safety issues because of their flammability, especially as researchers try to pack more energy in a smaller battery volume. Building batteries with a solid electrolyte, as ORNL researchers have demonstrated, could overcome these safety concerns and size constraints.

"To make a safer, lightweight battery, we need the design at the beginning to have safety in mind," said ORNL's Chengdu Liang, who led the newly published study in the Journal of the American Chemical Society. "We started with a conventional material that is highly stable in a battery system -- in particular one that is compatible with a lithium metal anode."

The ability to use pure lithium metal as an anode could ultimately yield batteries five to 10 times more powerful than current versions, which employ carbon based anodes.

"Cycling highly reactive lithium metal in flammable organic electrolytes causes serious safety concerns," Liang said. "A solid electrolyte enables the lithium metal to cycle well, with highly enhanced safety."

The ORNL team developed its solid electrolyte by manipulating a material called lithium thiophosphate so that it could conduct ions 1,000 times faster than its natural bulk form. The researchers used a chemical process called nanostructuring, which alters the structure of the crystals that make up the material.

"Think about it in terms of a big crystal of quartz vs. very fine beach sand," said coauthor Adam Rondinone. "You can have the same total volume of material, but it's broken up into very small particles that are packed together. It's made of the same atoms in roughly the same proportions, but at the nanoscale the structure is different. And now this solid material conducts lithium ions at a much greater rate than the original large crystal."

The researchers are continuing to test lab scale battery cells, and a patent on the team's invention is pending.

"We use a room-temperature, solution-based reaction that we believe can be easily scaled up," Rondinone said. "It's an energy-efficient way to make large amounts of this material."

The study is published as "Anomalous High Ionic Conductivity of Nanoporous β-Li3PS4," and its ORNL coauthors are Zengcai Liu, Wujun Fu, Andrew Payzant, Xiang Yu, Zili Wu, Nancy Dudney, Jim Kiggans, Kunlun Hong, Adam Rondinone and Chengdu Liang. The work was sponsored by the Division of Materials Sciences and Engineering in DOE's Office of Science
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