By William Fellows
Researchers at IBM Corp are pursuing the practical realization of their theoretical work in quantum information and computation theory by undertaking a feasibility study for the construction of a quantum computer (see separate story). But what will it actually mean?
One short-to-medium term application of quantum computing will be in security systems. Quantum cryptography is an area that researchers including IBM Fellow Charlie Bennett have been working on. Because quantum information cannot be read without disturbing it, an eavesdropper attempting to extract information from the encoded data will always be detected. In this way the security of information transfer can be guaranteed. That’s a lot safer than current cryptographic techniques that rely on mathematical theory, to which exceptions can sometimes be found or new theories found that invalidate existing work.
IBM researcher, Nabil Amers who is leading the team that will test for the feasibility of constructing a quantum computer says: We are in trouble using pure math. That doesn’t mean current security models are going to disappear overnight. Hybrid technologies drawing on quantum and conventional mathematical techniques will prevail initially, Amers believes. Indeed, IBM has already prototyped some work which it is to put on a circuit board and install on a card in servers. Bennett is also one an international group of six quantum scientists which confirmed the intuitions of the majority of science fiction writers by showing that perfect teleportation is indeed possible in principle, but only if the original is destroyed.
A web search will uncover a plethora of companies doing or offering quantum computing of one kind or another. They’re not, says Amers, who warns that while quantum computing by its nature will use small (atomic parts), minituratzation of the kind which takes place as a matter of course in the IT industry is most definitely not quantum computing.
Serious work on applying quantum theory to computing began when Paul Benioff of Argonne National Laboratory published a quantum mechanical model for computation in 1980. By 1994, Peter Shor’s theory had proved decoherence. In classic quantum mechanics, the observation of an event changes what that effect of that event would otherwise would have been. Shor’s algorithm operates in such a way that it allows the possibility that scientists can create systems that are isolated from such effects. Error correction, another bug-bear of computer science in which the precise use of zeros and ones is so important has been overcome; at least error-correction codes have been tested experimentally. Over at Bell Labs, researcher Lov Grover has tested the operation of five qubit using his algorithm. Qubit is quantum scientists’ lingo for a quantum bit, one that can hold a zero and one at the same time. The algorithms, modest working models, can be viewed as models for the programming environment through which a quantum computer will be told what to do.
Borrowing from a host of online material, quantum systems can be explained as those able to simultaneously occupy different quantum states – known as a superposition of states. Systems in this state are said to be coherent. Quantum mechanics deals with forces – literally the smallest – that operate at an atomic level. These laws are different – even diametrically opposed – to Newtonian laws, which apply to general observable physical behavior. From a physical point of view, a bit is a physical system which can be prepared in one of the two different states representing two logical values – no or yes, false or true, or 0 or 1.
In digital computers, the voltage between the plates in a capacitor represents a bit of information: a charged capacitor denotes bit value 1 and an uncharged capacitor bit value 0. If an atom is chosen to represent a physical bit then quantum mechanics dictates that apart from the two distinct electronic states the atom can be also prepared in a coherent superposition of the two states. This means that the atom is both in state 0 and state 1. Imagine a classical register composed of three physical bits. Any classical register of this type can store in a given moment of time only one out of eight different numbers. In other words the register can be in only one out of eight possible configurations such as 000, 001, 010, … 111. A quantum register composed of three qubits can store in a given moment of time all eight numbers in a quantum superposition. Three qubits can store eight different numbers at once, four qubits can store 16 different numbers at once, and so on; in general L qubits can store 2L numbers at once.
Making quantum mechanics and therefore quantum computing sensible still requires some further theoretical – and perhaps semantic – development. Simply put, if the rules of quantum theory are applied to large objects they give you nonsense. They will tell you that a baseball can be here and there at the same time, explains noted Oxford University scientist Dr Roger Penrose. He firmly believes that within 50 years quantum mechanics will spark a revolution in physics but still thinks the theory is just not right and that there is a level that things go over from the quantum to the classical. He says he it is possible to estimate what those levels are and has proposals for experiments which would determine whether this is right or not. á
