openqasm/examples/adder.qasm

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/*
* quantum ripple-carry adder
* Cuccaro et al, quant-ph/0410184
*/
include "stdgates.inc";
gate majority a, b, c {
cx c, b;
cx c, a;
ccx a, b, c;
}
gate unmaj a, b, c {
ccx a, b, c;
cx c, a;
cx a, b;
}
qubit[1] cin;
qubit[4] a;
qubit[4] b;
qubit[1] cout;
bit[5] ans;
uint[4] a_in = 1; // a = 0001
uint[4] b_in = 15; // b = 1111
// initialize qubits
reset cin;
reset a;
reset b;
reset cout;
// set input states
for uint i in [0: 3] {
if(bool(a_in[i])) x a[i];
if(bool(b_in[i])) x b[i];
}
// add a to b, storing result in b
majority cin[0], b[0], a[0];
for uint i in [0: 2] { majority a[i], b[i + 1], a[i + 1]; }
cx a[3], cout[0];
for uint i in [2: -1: 0] { unmaj a[i],b[i+1],a[i+1]; }
unmaj cin[0], b[0], a[0];
measure b[0:3] -> ans[0:3];
measure cout[0] -> ans[4];