First evidence for entanglement of three macroscopic objects has been seen in a superconducting circuit built at the University of Maryland. By examining an electrical circuit operating at temperatures near absolute zero, the researchers have found new evidence that the laws of quantum mechanics apply not just to microscopic particles such as atoms and electrons, but also to large electronic devices called superconducting quantum bits (qubits).

There is, to be sure, a genuine problem in the phenomenon of quantum measurement, but I will not discuss it here. It concerns introspective systems, where subject = object so that the basic conception of a single subject observing an ensemble of objects must be modified.
- David Finkelstein

Quantum information processing is at the crossroads of physics, mathematics and computer science. It is concerned with that we can and cannot do with quantum information that goes beyond the abilities of classical information processing devices. Communication complexity is an area of classical computer science that aims at quantifying the amount of communication necessary to solve distributed computational problems. Quantum communication complexity uses quantum mechanics to reduce the amount of communication that would be classically required.

Pseudo-telepathy is a surprising application of quantum information processing to communication complexity. Thanks to entanglement, perhaps the most nonclassical manifestation of quantum mechanics, two or more quantum players can accomplish a distributed task with no need for communication whatsoever, which would be an impossible feat for classical players.

After a detailed overview of the principle and purpose of pseudo-telepathy, we present a survey of recent and no-so-recent work on the subject. In particular, we describe and analyse all the pseudo-telepathy games currently known to the authors.

Including cause-and-effect in equations produces 4-dimensional space-time.

Is causality an inherent and necessary characteristic of the Universe, or just an illusion produced by the way our brains interpret the world?

It's real, say physicists, who believe they have worked out how the Universe is constructed from the tiniest building-blocks of space-time. The finding could also help the development of a theory of quantum gravity, which would marry the two currently estranged physical theories of the Universe: quantum theory and relativity.

Quantum theory describes the Universe at the tiniest possible scale - about 10-35 metres (about 1020 times smaller than the radius of a proton). It predicts that on this scale the apparently smooth fabric of space and time must degenerate into a kind of 'foam' in which connections between different points are constantly appearing and vanishing.

Physicists have long been trying to figure out how the fuzzy nature of space-time at this tiny scale can give rise to the large four-dimensional Universe we see around us, as described by Einstein's theory of relativity.

Scientists studying the problem assume that each tiny piece of the foam is a kind of four-dimensional triangle, with three dimensions of space and one corresponding to time. The smooth fabric of space-time can be built up by gluing these triangular tiles together, just as a smoothly curved surface can be made from flat, two-dimensional tiles.

Because the quantum foam fluctuates through all kinds of configurations, constructing the physical Universe means adding up all the possible tiling patterns. You might think that this would inevitably generate a four-dimensional Universe - but it doesn't. Earlier researchers found that they got a space-time with either an infinite number of dimensions or just two. Neither of these looks at all like our Universe.

Construction work

Renate Loll of Utrecht University in the Netherlands and her co-workers have now found a way to assemble the pieces so that they inevitably produce a four-dimensional Universe. Instead of assuming that all tilings are allowed, they impose two constraints.

First, the theory of relativity must apply within each individual tile (so that nothing can travel through it faster than light) and second, the assembly must preserve causality. This means that a piece of space-time cannot be constructed in such a way that an 'event' - some change in the Universe - precedes its cause.

A joint research project of Fujitsu Ltd. and The University of Tokyo has made progress towards realizing a viable quantum cryptography system. Such a system allows parties to share encryption keys via telecommunication networks with full confidence that they have not been compromised en route.

The team has succeeded in generating and detecting a single photon at wavelengths useful for telecommunications, said Yasuhiko Arakawa, director of the Nanoelectronics Collaborative Research Center at The University of Tokyo and leader of the research project, in an interview on Tuesday.

The fastest known cryptographic system based on transmission of single photons---the smallest pulses of light---has been demonstrated by a team at the Commerce Department's National Institute of Standards and Technology (NIST). The transmissions cannot be intercepted without detection, so that messages encrypted with the system can be kept secret.

The NIST "quantum key distribution" (QKD) system transmits a stream of individual photons to generate a verifiably secret key--a random series of digital bits, each representing 0 or 1, used to encrypt messages--at a rate of 1 million bits per second (bps). This rate is about 100 times faster than previously reported systems of this type.

The demonstration, described in the May 3 issue of Optics Express,* is the first major reported result from a new NIST testbed built to demonstrate quantum communications technologies and cryptographic key distribution.

General relativity may seem very different from quantum theory, but work on quantum gravity has revealed a deep analogy between the two. General relativity makes heavy use of the category nCob, whose objects are (n-1)-dimensional manifolds representing "space" and whose morphisms are n-dimensional cobordisms representing "spacetime". Quantum theory makes heavy use of the category Hilb, whose objects are Hilbert spaces used to describe "states", and whose morphisms are bounded linear operators used to describe "processes". Moreover, the categories nCob and Hilb resemble each other far more than either resembles Set, the category whose objects are sets and whose morphisms are functions. In particular, both Hilb and nCob but not Set are *-categories with a noncartesian monoidal structure. We show how this accounts for many of the famously puzzling features of quantum theory: the failure of local realism, the impossibility of duplicating quantum information, and so on. We argue that these features only seem puzzling when we try to treat Hilb as analogous to Set rather than nCob, so that quantum theory will make more sense when regarded as part of a theory of spacetime.

In the golden years of the Liberal Party in England, before the First World War, Herbert Asquith was the patrician prime minister and Winston Churchill was an obstreperous young politician. At question time in the House of Commons, Churchill frequently challenged Asquith with provocative statements and awkward questions. After one of these Churchillian assaults, Asquith lamented, "I wish I knew as much about anything as that young man knows about everything." Reading this eloquent book in which Brian Greene lays out before us his vision of the cosmos, I feel some sympathy for Asquith. Asquith expresses my reaction to the book precisely.

The quantum states of atoms and subatomic particles that prototype quantum computers use to represent the 1s and 0s of computer information are so fragile that the energy from heat, light and magnetism ordinarily found in their environments is usually enough to change them, effectively stuffing out the information they hold.

Rather than fight the odds, many researchers are working with the environmental noise to create safe havens for quantum bits, or qubits. Particles like atoms, electrons and photons can be used as qubits because they can be oriented in one of two directions -- spin up and spin down. Qubits can also be encoded in the interactions of pairs of particles. The key to making protected qubits is to encode logical qubits in multiple physical qubits.

These approaches are central to efforts aimed at making viable quantum computers, said Jason Ollerenshaw, a researcher at the University of Toronto in Canada. "Techniques for resisting environmental noise will be essential in building quantum computers on a practical scale," he said. Quantum computers hold the promise of solving certain types of problems like cracking secret codes that are far beyond the reach of ordinary computers.

Ollerenshaw and his colleagues at the University of Toronto have built a prototype quantum computer that can execute a quantum search algorithm despite environmental noise. "We have experimentally demonstrated that a quantum computer can be protected from decoherence -- the detrimental effects of environmental noise -- during the course of a complete quantum computation," said Ollerenshaw.

Researchers have overcome a major obstacle to generating random numbers on quantum computers by limiting the possibilities in the otherwise unlimited randomness of a set of quantum particles.

Random numbers play a key role in classical computing by providing an element of chance in games and simulations, a reliable method for encrypting messages, and a means of accurately sampling huge amounts of data.

Researchers from the Massachusetts Institute of Technology and the National Atomic Energy Commission in Argentina have shown that short sequences of random operations—randomly shifting laser pulses or magnetic fields—acting on a string of quantum bits can, in effect, generate random configurations of qubits.

Eight years after physicists coaxed ultracold atoms into a new type of matter in which thousands of atoms slide into the perfect lock step behavior of a single superparticle, two research teams have now repeated the feat using small molecules.

According to new research from Rice University, scientists studying the way light interacts with metallic nanostructures should throw out their old optics textbooks and bone up on their quantum mechanics instead.
The new findings, which are described in the Oct. 17 issue of the journal Science, offer a new understanding of plasmonics, an emerging field of optics aimed at the study of light at the nanometer scale -- at dimensions far smaller than a wavelength of light, smaller than today's smallest electronic devices. Rice's findings will make it easier for scientists and engineers to design new optical materials and devices "from the bottom up," using metal particles of specifically tailored shapes.

A successful solid-state quantum computer will have to 'entangle' quantum bits - or 'qubits' - over macroscopic distances. However, entanglement in solid-state systems has only been observed on the micrometre scale so far. Now, Andrew Berkley and colleagues from the University of Maryland have entangled two solid-state superconducting qubits over a distance of 0.7 mm - a thousand times greater than ever before (A J Berkley et al. 2003 Sciencexpress 1084528 ).

Japan's NEC Corp and a public research body said on Thursday they had made a technological breakthrough that brought ultra-fast quantum computers a step closer.

Quantum computers, when brought into practical use, are expected to far surpass the capabilities of today's most powerful supercomputers, particularly in fields such as data mining, or searching large databases for particular pieces of information.

However, an NEC spokesman said that quantum computers for commercial use were unlikely to be available before 2020.

Quantum computers use 'qubits' -- forms of quantum particles -- as the basic information unit and these will eventually be more flexible and faster in processing information than existing computer processes.