On the gate complexity of reversible circuits consisting of NOT, CNOT and 2-CNOT gates
Dmitry Vladimirovich Zakablukov · Discrete Mathematics and Applications · 2017
Abstract The paper is concerned with the problem of complexity of reversible circuits consisting of NOT, CNOT and 2-CNOT gates. For a reversible circuit implementing a map f : Z 2 n → Z 2 n $f: \mathbb Z_2^n\, \to\, \mathbb Z_2^n$ we define the Shannon complexity function L ( n , q ) as a function of n and the number q of additional inputs in the circuit. We prove the lower estimate L ( n , q ) ⩾ 2 n ( n − 2 ) 3 log 2 ( n + q ) − n 3 $L(n,q)\, \geqslant\, \displaystyle\frac{2^n(n-2)}{3\log_2(n+q)} - \frac{n}{3}$ for the complexity of a reversible circuit and derive the upper estimate L ( n , 0) ⩽ 48 n 2 n (1 + o (1)) / log 2 n if there are no additional inputs. The asymptotic upper estimate for the complexity is shown to be L ( n , q 0 ) ≲ 2 n with q 0 ∽ n 2 n − o ( n ) additional inputs.