Quantum computation model has been anticipated as a compact way of representing exponential amount of information in polynomial succinctness, and carrying out multiple computation simultaneously. This is affected by manipulating superposed information through reversible/unitary transformations. In this paper, we use this succinctness of such a model of computation to encode (i) multiple possible input patterns into one superposed input, (ii) encode circuit computation as unitary evolution operations, and (iii) read multiple outputs by unentangling the superposed output. This allows us to compute the probability values of various possible states at the output for various possible input probability distributions. Thus, the reliability of the circuit being modeled can be computed, in terms of the entropy at the entangled output. At the outset this might seem quite convoluted, but we argue in this paper that this model of computation provides an effective and compact way of reliability evaluation, based on our previous work on analyzing reliability of defect-tolerant architectures by exploiting various other models of computation.