Table 1 A truth table of the reversible Fredkin gate.

From: All-optical design for inherently energy-conserving reversible gates and circuits

C

X 1

X 2

C ′

Y 1

Y 2

0

0

0

0

0

0

0

0

1

0

0

1

0

1

0

0

1

0

0

1

1

0

1

1

1

0

0

1

0

0

1

0

1

1

1

0

1

1

0

1

0

1

1

1

1

1

1

1

  1. X1, X2 and C represent three input bits, while Y1, Y2 and C′ represent three output bits.