From: mr Squigle 9/11/99 19:24:03 Subject: quantam computers post id: 5966 i have heard a bit about these from people i know at uni. But they have always had differnet expliantions any one want to explain them to me? From: Grant¹ 9/11/99 19:50:30 Subject: re: quantam computers post id: 5973 If this link works, it will take you to a previous thread on this topic, bursting with informative goodness. Otherwise you'll get an error message or something. 8^) From: scott 10/11/99 0:26:00 Subject: re: quantam computers post id: 6068 Quantum computation? A fundamentally new mode of information processing that can be performed only by harnessing physical phenomena unique to quantum mechanics (especially quantum interference). What will quantum computers be good at? These are the most important applications currently known: Cryptography: perfectly secure communication. Searching, especially algorithmic searching (Grover's algorithm). Factorising large numbers very rapidly (Shor's algorithm). Simulating quantum-mechanical systems efficiently. If you only want to predict what quantum computers will be able to do, you only need the equations of quantum mechanics. But if you want to explain how they will do it, you need to understand that the computer you can see and touch is only one tiny facet of a far larger object, which is just as real even though its existence is only detectable indirectly, through the computational work it does for us. It has the structure of many computers similar to the one we see, performing different computations which affect each other through quantum interference. In quantum computers, the effects of quantum interference are writ large. But the theory says that the whole of reality behaves in the same way. So the whole universe that we see around us is only a tiny facet of a much larger entity, the multiverse, which contains many universes like ours, interacting only through quantum interference. I can give you more if you like? quantum mechanics? The deepest theory of physics; the framework within which all other current theories, except the general theory of relativity, are formulated. Some of its features are: Quantisation: (which means that observable quantities do not vary continuously but come in discrete chunks or 'quanta'). This is the one that makes computation, classical or quantum, possible at all. Interference: (which means that the outcome of a quantum process in general depends on all the possible histories of that process). This is the one that makes quantum computers qualitatively more powerful than classical ones. Entanglement: (which means that the properties of a composite system, even when the components are distant and non-interacting, cannot in general be fully expressed by descriptions of the properties of all the component systems). The is the one that makes quantum cryptography possible. From: Chris 10/11/99 23:48:11 Subject: re: quantam computers post id: 6348 Each processing unit in today's computers can only perform one operation at a time. For example, in a PC the main processor (Pentium chip or whatever) can do something like fetch two numbers from memory, add them then store the result. The apparent ability to do lots of things at once comes from the fact that the computer can perform perhaps 100 million operations like this per second. If you want a faster computer, one way to do it is to add more processors. For example, if you need to add 32 pairs of numbers together then instead of having one processor do each pair in turn, you can have 32 processors each handle one pair of numbers. This is called parallel processing. The basic idea of a quantum computer is to build a single processor which can do many operations like this in one step. This would be made possible by a new type of memory. In a normal computer a single memory location (or bit) is always either on or off. But quantum objects like atoms and electrons can exist in a superposition of states, so that a qubit (quantum bit) could be on AND off at the same time. This means that a single memory location made up of, say 32 qubits, could represent 2^32 or 4,294,967,296 numbers simultaneously. A quantum processor could then operate on all these numbers in one step, which is essentially equivalent to having 4 billion "normal" processors each doing one number. There are many problems associated with actually building a quantum computer, although people are currently working on solutions. One of the main problems is keeping the qubits in the required "coherent superposition" of states long enough to do a calculation. Also, basic logic gates need to be redesigned in order to preserve the superposition of states. It is likely that sooner or later the problems will be solved. The question then will be "What good is a quantum computer?" Currently, people have only come up with a few applications for which quantum computers would be especially suited. Some of these have been mentioned above. For example, the problem of decrypting encoded data (without knowing the code key in advance) is a practically unsolvable one with present technology, due to the large number of calculations required to discover the key. A quantum computer would solve the problem neatly by trying all possible keys at once. JR This forum is un-moderated. The views and opinions expressed are those of the individual poster and not the ABC. The ABC reserves the right to remove offensive or inappropriate messages.