## Quantum Mechanical Computers

In this chapter, the authors discuss the part in an effort to analyze the physical limitations of computers due to the laws of physics. It is a result of computer science that a universal computer can be made by a suitably complex network of interconnected primitive elements. A more elaborate circuit is a full adder which takes a carry, c, and adds it to the two lines a and b and has an additional line, d, with a 0 input. Calculations can be done with reversible machines containing only reversible primitives. There are many sources of imperfections in the machine, but the first one people would like to consider is the possibility that the coefficients in the couplings, along the program line, are not exactly equal. The switches are represented by diagonal lines, and in boxes put the other matrices that operate on registers such as the NOT b.