Alternative Quantum Computer Architectures

Thinking ahead about what is coming in QC, I should mention that there are different ways of designing QCs. So far, we have described QCs based on quantum gates interacting with qubits. Quantum gate architecture is much like the architecture in classical computers. But there are other ways qubits can be manipulated and measured for computational purposes. These alternative structures may turn out to be faster or more easily implemented than the gated-based structures that have been used so far. Moreover, alternative architectures may help circumvent noise, loss, and decoherence effects.

As one alternative, we have already mentioned briefly, there is the possibility of using quantum systems with more than two states. It turns out there are some advantages of using these multi-state systems in terms of energy efficiency, coding flexibility, and a reduction in susceptibility to noise and other decoherence effects. But so far, it is qubit (two-state) technology and algorithms based on qubit manipulation that have dominated QIS and QC. Developing technologies to produce qutrits in specified states and getting them involved in entangled states is still in the development stage. But we believe this is an aspect of QIS and QC that may take off in the next decade or so.