Amazon Book Description
- Following on from his bestseller, "Gribbin (John) - In Search Of 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 teleportation1 machine.
ContentsACKNOWLEDGEMENTS – vi
PREFACE – vii
- PROLOGUE: THE PROBLEM - 1
The light fantastic; Electronic interference; The standard view; The cat in the box; Another aspect of reality; The daughters of Schrodinger’s cat.
- CHAPTER ONE: ANCIENT LIGHT – 31
The first modern scientist; From Woolsthorpe to Cambridge – and back; In Newton’s shadow; Newton’s view of the world; Young ideas; Fresnel, Poisson, and the spot; The bookbinder’s apprentice; Faraday’s fields; The colours of magic; Maxwell’s amazing equations.
- CHAPTER TWO: MODERN TIMES – 68
The death of the ether; Towards a special theory of relativity; Einstein’s insight; Faster than light/backwards in time; Enter the photon; The man who taught Einstein to count photons; The strange theory of light and matter, The triumph of QED; Light of future days.
- CHAPTER THREE: STRANGE BUT TRUE – 108
Seeing impossible light; Shedding more light on light; Seeing double; Something for nothing; ‘Beam me aboard, Scotty2’; Quantum cryptography; Inside the photon; Watching the quantum pot; The great electronic round-up; When is a photon?
- CHAPTER FOUR: DESPERATE REMEDIES – 145
The Copenhagen collapse; I think, therefore; Von Neumann’s silly mistake; The undivided whole; A proliferation of universes; Variations on a quantum theme; Counsels of despair; A relativistic aside; An experiment with time.
- CHAPTER FIVE: THINKING ABOUT THINKING ABOUT THINGS – 184
Constructing quarks; Putting Einstein in perspective; Getting a grip on reality; The bulk-buying approach to quantum reality.
- EPILOGUE: THE SOLUTION – A MYTH FOR OUR TIMES – 225
Making the most of mass; The simple face of complexity; Shaking hands with the Universe; Taking time to make time.
- BIBLIOGRAPHY – 248
- INDEX – 255
Book Comment
Phoenix; New Edition (3 April 2003); Paperback
"Gribbin (John) - Schrodinger's Kittens: Teletransportation"
Source: Gribbin (John) - Schrodinger's Kittens and the Search for Reality, pp. 125-7
Excerpts (pp. 125-127) ‘Beam Me Aboard, Scotty’
- I love the combination of the simplicity of the idea behind this experiment1 and the fine-scale subtlety of the way it was put into practice (and the fact that it shows quantum theory, once again, triumphant). It took more than 40 years from the time that theorists came up with the idea before experimenters could test it, but it was well worth the wait. It may take at least that long for some of the current crop of theoretical ideas to be tested, but those experiments, if they ever are carried out, will be even more spectacular. Would you believe, for example, that quantum theory tells us that teleportation - yes, ‘Beam me up, Scotty’ teleportation, just like in Star Trek - may actually be possible?
- Remember the EPR ‘thought experiment’, that was actually put into practice by Alain Aspect and his colleagues? They showed that a pair of photons which are produced in such a way that they must have opposite polarizations - but nobody knows what the polarizations are - remain in an entangled state as they fly in opposite directions across the Universe. When the polarization of one of the photons is measured, the other one, instantaneously, collapses into the opposite state. This entanglement and action at a distance is at the heart of the technique of quantum teleportation proposed by Charles Bennett, of the IBM Research Center at Yorktown Heights in New York, and published in the highly respectable journal Physical Review Letters in 1993. Apart from its science-fiction-like overtones, the important point about this work is that the team showed how to solve what seemed an insuperable quantum problem, using quantum techniques themselves.
- In the classical, everyday world sending copies of things to distant places is routine. The obvious analogy with teleportation is the fax machine, which has the added advantage of leaving the original copy intact at its starting place while producing a duplicate at the destination. Newspapers and books are reproduced in editions containing hundreds of thousands of essentially identical copies, as far as their information-content is concerned. But at the quantum level, copying runs into difficulties.
- The first is simply a question of detail. The uncertainty principle makes it impossible to know every detail about every atom in, say, a sheet of paper, or even the exact position of every molecule of ink in the printing on the paper; so the faxed ‘copy’ can only ever be an approximation. In addition, scanning an object at the quantum level changes its quantum state - the very act of looking at something alters it, according to quantum theory. So even if you did obtain the information needed to build a copy of a quantum system, the original would be destroyed. In a way, this is actually more like the SF version of teleportation than the way a fax machine works. In SF, it is usually an essential feature of teleportation that the ‘original’ is destroyed - although several stories have looked at the unpleasant consequences of using teleportation devices to create multiple copies of human beings.
- Classical information can be copied, but can only be transmitted at the speed of light (or less); quantum information cannot be copied (‘a single quantum cannot be cloned’, as the physicists quip), but sometimes, as in the EPR experiment, it seems to propagate instantly from one place to another. Bennett and his colleagues used a mixture of these classical and quantum features of a system to propose their teleportation device.
- They describe this in terms of two people, Alice and Bob, who want to teleport an object. In this teleportation for beginners, the object to be teleported is simply a single particle - perhaps an electron - in a particular quantum state. At the beginning of the experiment, Alice and Bob are each given a box containing one member of a pair of entangled objects, equivalent to them each carrying one of the photons from the EPR experiment, without measuring its polarization. Then they go off on their travels across the Universe. Sometime later - perhaps many years later - Alice wants to send another particle to Bob. All she has to do is to allow the ‘new’ particle to interact with her entangled particle, and to measure the outcome of their interaction. This both establishes and changes the state of her entangled particle, and instantaneously establishes and changes the state of Bob’s entangled particle in an equivalent way.
- Bob doesn’t know this yet, because he is somewhere on the other side of the Universe. So now Alice has to send him a message, perhaps by radio, or perhaps by putting a notice in the newspaper that Bob reads every day, telling him the result of her measurement. This message contains only classical information, so she can send as many copies as she likes in as many newspapers or radio broadcasts as she likes. Eventually, Bob will get the message. Armed with the information about how the interaction between Alice’s two particles turned out, Bob can now look at his own entangled particle and use the information to ‘subtract out’ the influence of his own original particle from its present state. What he is left with is an exact copy of the other particle - the one that Alice wanted to send to him. And she has done this without knowing where Bob is, or even speaking to him directly. The original version of the third particle was destroyed (changed into another quantum state) when Alice carried out her measurement on it, so Bob’s version is unique, unlike a newspaper, and he is fully entitled to regard it as the original particle, conveyed to him by a combination of classical message and action at a distance.
- This, Bennett stresses, defies no physical laws, and only permits teleportation to take place at less than the speed of light - Bob needs Alice’s ‘classical’ message in order to untangle his particle properly, and if he looks at his particle too soon he will change its quantum state and destroy any prospect of untangling it in the right way. ‘Alice’s measurement forces the other EPR particle to change in such a way that the classical information that comes out of her measurement enables someone else to produce a perfect copy of what went in,’ but ‘it cannot take place instantaneously2.” It is, as one wag has remarked, ‘teleportation, Jim, but not as we know it’. Given the ingenuity of the experimenters, though, there must be a good chance that before 40 more years have passed they will be sending electrons from one side of the lab to the other, or even around the world (if not across the Universe) in this way. It will be a neat trick, even if it has no practical implications. But there may even be practical implications, if not for this specific work then certainly for some related investigations of the mysteries of the quantum world. Bennett’s fertile imagination does not stop at teleportation, and one of his other achievements, more obviously associated with the interests of IBM itself, concerns the possibility of using quantum mechanics to create an uncrackable code.
Inspecting teleported quantum information
- It’s a stock scene in many science-fiction films and novels: A mysterious alien vanishes from one location, while a perfect replica shimmers into existence somewhere else. Science fiction has long relied on teleportation to provide this convenient shortcut. Now, researchers have uncovered a new consequence of quantum theory that makes it possible, in principle, to achieve “quantum teleportation" of information.
- “It’s a means by which you can take apart an unknown quantum state into classical information and purely quantum information, send them through two separate channels, put them back together, and get back the original quantum state,” says Charles H. Bennett of the IBM Thomas J. Watson Research Center in Yorktown Heights, N.Y.
- Bennett and his collaborators describe their scheme in the March 29 Physical Review Letters.
- The notion of quantum teleportation hinges on the distinction between classical information (the kind conveyed by a newspaper or some other conventional medium) and quantum information (the kind represented by such characteristics as a microscopic particle's spin or a photon's polarization angle).
- Classical information can be freely copied. It's not disturbed when observed, and it can't travel faster than the speed of light. In contrast, quantum information can't be observed without being disturbed, nor can it be copied reliably. “And it sometimes seems to propagate instantaneously,” Bennett remarks.
- The notorious Einstein-Podolsky- Rosen (EPR) effect stands as one of the more bizarre manifestations of this quantum waywardness (SN: 8/5/89, p.88). For example, suppose a single process within an atom simultaneously generates two photons that travel in opposite directions. According to quantum theory, neither photon has a particular polarization, or electric field orientation, until it’s measured at a detector.
- In fact, such a measurement transforms a photon’s polarization from a range of possibilities into a specific, randomly chosen value. Surprisingly, measuring one photon's polarization causes the other photon of the EPR pair to acquire the opposite polarization at the same instant-even if the second photon is at the other end of the room or across the galaxy. “This is a phenomenon that cannot be explained by assuming that the two [photons] had [particular] polarizations at the moment they were created,” Bennett notes.
- Although this effect can’t be harnessed to send controllable, faster-than-light messages, Bennett and his colleagues argue that it can be used to assist in the teleportation of information about a particle’s quantum state.
- The sender, Alice, wants to convey to the receiver, Bob, a certain photon's unknown polarization. Instead of determining its polarization directly, and thereby disturbing it, she measures the relationship between the polarization angle of her mystery photon and that of a photon created in an EPR process. She then sends a message to Bob, using a conventional medium, to tell him that the two polarization angles are identical, are at right angles to each other, or have one of two other possible geometrical relationships.
- Meanwhile, Bob has access to the second EPR photon. He can combine the classical information contained in Alice’s message with the quantum information carried by his own EPR photon. This combination allows him to transform the quantum state of his EPR photon, which has never been anywhere near Alice’s mystery photon, into an exact replica of the mystery photon's original quantum state. In effect, “Alice’s measurement forces the other EPR particle to change in such a way that the classical information that comes out of her measurement enables someone else to produce a perfect copy of what went in," Bennett says.
- However, although the EPR information travels instantly, the entire scheme still requires a finite amount of time. “It must be emphasized that our teleportation, unlike some science-fiction versions, defies no physical laws,” the researchers say. “In particular, it cannot take place instantaneously ... because it requires, among other things, sending a classical message from Alice to Bob"
- Though of no practical value, this exercise in quantum logic helps elucidate the crucial differences between classical and quantum information, Bennett says.
→ I. Peterson, Science News, April 10, 1993
Paper Comment
A printout is held in "Various - Papers on Desktop".
In-Page Footnotes ("Gribbin (John) - Schrodinger's Kittens: Teletransportation")
Footnote 1:
- This was an experiment to test the influence of the vacuum field – ‘nothing at all’ – on individual sodium atoms.
Footnote 2:
Text Colour Conventions (see disclaimer)- Blue: Text by me; © Theo Todman, 2025
- Mauve: Text by correspondent(s) or other author(s); © the author(s)