Following on from his bestseller, SCHRODINGER'S CAT, John Gribbin presents the recent dramatic improvements in experimental techniques that have enabled physicists to formulate and test new theories about the nature of light. He describes these theories not in terms of hard-to-imagine entities like spinning subnuclear particles, but in terms of the fate of two small cats, separated at a tender age and carried to opposite ends of the universe. In this way Gribbin introduces the reader to such new developments as quantum cryptography, through which unbreakable codes can be made, and goes on to possible future developments such as the idea that the 'entanglement' of quantum particles could be a way to build a STAR TREK style teleportation machine.
Following on from his bestseller, SCHRODINGER'S CAT, John Gribbin presents the recent dramatic improvements in experimental techniques that have enabled physicists to formulate and test new theories about the nature of light. He describes these theories not in terms of hard-to-imagine entities like spinning subnuclear particles, but in terms of the fate of two small cats, separated at a tender age and carried to opposite ends of the universe. In this way Gribbin introduces the reader to such new developments as quantum cryptography, through which unbreakable codes can be made, and goes on to possible future developments such as the idea that the 'entanglement' of quantum particles could be a way to build a STAR TREK style teleportation machine.
Quantum theory is so shocking that Einstein could not bring himself to accept it. It is so important that it provides the fundamental underpinning of all modern sciences. Without it, we'd have no nuclear power or nuclear weapons, no TV, no computers, no science of molecular biology, no understanding of DNA, no genetic engineering. In Search of Schrodinger's Cat tells the complete story of quantum mechanics, a truth stranger than any fiction. John Gribbin takes us step by step into an ever more bizarre and fascinating place, requiring only that we approach it with an open mind. He introduces the scientists who developed quantum theory. He investigates the atom, radiation, time travel, the birth of the universe, superconductors and life itself. And in a world full of its own delights, mysteries and surprises, he searches for Schrodinger's Cat - a search for quantum reality - as he brings every reader to a clear understanding of the most important area of scientific study today - quantum physics. In Search of Schrodinger's Cat is a fascinating and delightful introduction to the strange world of the quantum - an essential element in understanding today's world.
Schrödinger's cat has always been an elusive beast, but physicists may have finally trapped one in the laboratory. In the great Austrian physicist's thought experiment, the fate of a cat was linked to the quantum indeterminacy of a radioactive atom—half decayed, half undecayed. The cat, as a result, was both alive and dead. Now physicists at the National Institute of Standards and Technology in Boulder, Colorado, report in this issue ( p. 1131 ) that they have created what one observer calls a “Schrödinger's kitten,” in which they excite an atom into a superposition of quantum states, then ease those two states apart so that the atom appears to be in two distinct physical locations simultaneously.
Introduction: about quanta, atoms, photons, and cats Experiments which manipulate and study isolated quantum systems have come of age. We can now trap single atoms or photons in a box, entangle them together, observe directly their quantum jumps, and realize in this way some of the thought-experiments imagined by the founding fathers of quantum physics. Schrödinger, who believed that observing an atom so to speak in vivo would remain forever impossible (Schrödinger 1952), would have been amazed, could he have seen what experimenters now achieve by manipulating atoms with lasers. These experiments are not just textbook illustrations of quantum concepts. They are considered by many as first steps towards harnessing the quantum world and realizing classically impossible tasks A quantum computer, for instance, would be a machine using quantum interference effects at a macroscopic scale in order to perform massive parallelism in computation (Nielsen and Chuang 2000). It would achieve an exponential speed-up to solve some problems such as the factoring of large numbers (Shor 1994). Such a machine would manipulate large ensembles of “quantum bits” made of atoms, molecules, or photons. Each bit would evolve in a superposition of two states labeled as “0” and “1”. These bits would be entangled together by quantum gates exploiting electromagnetic interactions between them. The behavior of this machine would be strange and counterintuitive. It would be a system made of thousands of two-level particles following during the calculation a huge number of different routes among which it remains coherently suspended.
Quantum mechanics is our most successful physical theory. It underlies our very detailed understanding of atomic physics, chemistry, and nuclear physics, and the many technologies to which physical systems in these regimes give rise. Additionally, relativistic quantum mechanics is the basis for the standard model of elementary particles, which very successfully gives a partial unification of the forces operating at the atomic, nuclear, and subnuclear levels. However, from its inception the probabilistic nature of quantum mechanics, and the fact that “quantum measurements” in the orthodox formulation appear to require the intervention of non-quantum mechanical “classical systems,” have led to speculations by many physicists, mathematicians, and philosophers of science that quantum mechanics may be incomplete. Among the Founding Fathers of quantum theory, Einstein and Schrödinger were both of the opinion that quantum mechanics is in some way unsatisfactory, and this view has been amplified in more recent profound work of John Bell, among others. In an opposing camp, many others in the physics, mathematics, and philosophy communities have attempted to provide an interpretational foundation in which quantum mechanics remains a complete and self-contained system. Among the Founding Fathers, Bohr, Born, and Heisenberg maintained that quantum mechanics is a complete system, and a number of recent proposals have been made to improve upon or to provide alternatives to their “Copenhagen Interpretation.” The debate continues, and has spawned an enormous literature.
How it all began In 1935, a decade after the invention of quantum theory by Heisenberg (1925) and Schrödinger (1926), three papers appeared, setting the stage for a new concept, quantum entanglement. The previous decade had already seen momentous discussions on the meaning of the new theory, for example by Niels Bohr (see his contribution to Albert Einstein: Philosopher-Scientist in Further reading); but these new papers opened up the gates for a new, very deep philosophical debate about the nature of reality, about the role of knowledge, and about their relation. Since the 1970s, it has become possible for experimenters to observe entanglement directly in the laboratory and thus test the counter-intuitive predictions of quantum mechanics whose confirmation today is beyond reasonable doubt. Since the 1990s, the conceptual and experimental developments have led to new concepts in information technology, including such topics as quantum cryptography, quantum teleportation, and quantum computation, in which entanglement plays a key role. In the first of the three papers, Einstein, Podolsky, and Rosen (EPR) realized that, if two particles had interacted in their past, their properties will remain connected in the future in a novel way, namely, observation on one determines the quantum state of the other, no matter how far away. Their conclusion was that quantum mechanics is incomplete and they expressed their belief that a more complete theory may be found. Niels Bohr replied that the two systems may never be considered independent of each other, and observation on one changes the possible predictions on the other. Finally, Erwin Schrödinger, in the paper which also proposed his famous cat paradox, coined the term “entanglement” (in German Verschränkung ) for the new situation and he called it “not one, but the essential trait of the new theory, the one which forces a complete departure from all classical concepts.”