QUANGLEMENT - КВАНТГЛЕМЕНТ

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The entangled quantum world

§23.10 23.10

indeed, is the only connecting link between us that is capable of supporting the amount of ‘information’ that is required. The trouble with it, of course, is that it contains a stretch that extends 5 years into the past!

23.10 Quanglement I must make it very clear that I am not trying to give support to the idea that ordinary information can be propagated backwards in time (nor can EPR effects be used to send classical information faster than light; see later). That kind of thing would lead to all sorts of paradoxes that we should have absolutely no truck with (I shall return to this kind of issue in §30.6). Information, in the ordinary sense, cannot travel backwards in time. I am talking about something quite diVerent that is sometimes referred to as quantum information. Now there is a diYculty about this term, namely the appearance of the word ‘information’. In my view, the preWx ‘quantum’ does not do enough to soften the association with ordinary information, so I am proposing that we adopt a new15 term for it: QUANGLEMENT At least in this book, I shall refer to what is commonly called ‘quantum information’ as quanglement. The term suggests ‘quantum mechanics’ and it suggests ‘entanglement’. This is very appropriate. This is what quanglement is all about. Quanglement also does have something very much to do with information, but it is not information. There is no way to send an ordinary signal by means of quanglement alone. This much is made clear from the fact that past-directed channels of quanglement can be used just as well as future-directed channels. If quanglement were transmittable information, then it would be possible to send messages into the past, which it isn’t. But quanglement can be used in conjunction with ordinary information channels, to enable these to achieve things that ordinary signalling alone cannot achieve. It is a very subtle thing. In a sense, quantum computing and quantum cryptography, and certainly quantum teleportation, depend crucially on the properties of quanglement and its interrelation with ordinary information. As far as I can make out, quanglement links are always constrained by the light cones, just as are ordinary information links, but quanglement links have the novel feature that they can zig-zag backwards and forwards in time,16 so as to achieve an eVective ‘spacelike propagation’. Since quanglement is not information, this does not allow actual signals to be sent faster than light. There is also an association between quanglement and ordinary spatial geometry (via the connections between the Riemann sphere and spin, as pictured in Figs. 22.10, 22.14, 22.16), this association 603


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