Computer is the information-processing machine that processes the input information to gives out the required output information. The input information are fed in the user's language and then converted to the machine language for the processing of the available information and then reconverted back to the users' language for the users' understanding and requirement. The fact that a real computer is a physical system prompts us to think about the space, time and energy implications of trying to make computers faster. To make computers faster, their components have to be squeezed closer together because the signals that need to be passed around inside the computer cannot travel faster than the speed of light. However, size is not the only issue. The components inside conventional computers give off a certain amount of heat as a side effect of their operation. If the components are simply packed closer together without also improving the energy efficiency the computer will melt itself as it computes! Solving either of these problems helps; solving both will be essential to achieve further miniaturization and speedup. Currently the computer industry is heading towards the exponential increase of transistors per chip and the memory capacity of a chip approximately doubled every one and half years even though a chip remained physically about the same size. Simultaneously the speed of the chips has been increasing exponentially. Extrapolating this trend suggests that the computers available in 2020 will operate at about 40 GHz!

If current trends in miniaturization and energy efficiency continue as they have for the last 20 to 30 years, by the year 2020, the basic memory components of a computer will be the size of individual atoms. At such scales, the theory of computations will become invalid. A new field called "quantum computing" is emerging that is reinventing the foundations of computer science and information theory in a way that is consistent with quantum physics-the most accurate model of reality that is currently known. At this point quantum effects will dominate every aspect of computer operation, from loading programs, running such programs and reading the answers. Even the design of algorithms will have to be rethought to make the best possible use of the quantum possibilities. Remarkably, this new theory predicts that quantum computers can perform certain tasks breathtakingly faster than classical computers and yet can accomplish mind-boggling feats such as teleporting information, breaking supposedly "unbreakable" codes, generating true random numbers and communicating with messages that betray the presence of eavesdropping.

Theoretically speaking, quantum computers are examples of what are called reversible computers. In principle any energy one needs to feed into them to do a particular computation should be redeemable at the end of computation, resulting in no net energy consumption. A more realistic advantages of a quantum computer over any classical computer (no matter how advanced) is that certain types of computation can be done using far fewer logical operations on a quantum computer than a classical computer. If one reduces the number of logical operations to achieve a given result, one might be able to save on the energy required for the computation. This is because quantum computers are able to work on all possible inputs to a program simultaneously and then extract partial information about all the different answers at the end. In contrast a classical computer has to work on each input separately. If there are many input all of which need to be tested, the energy savings could be appreciable.

Interestingly "quantum computing" is going to be the most challenging and productive field of interest in near future. For realizing this dream machine, a pool of quantum physicists and computer experts are the need of the time. Apart from this pool of experts the funding agencies should also play the most important role of funding. Then it is the matter of time that this dream machine will become a physical reality in our life time.