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Creating a NOT gate with five controls out of Toffoli gates and ancilla bits. Uncomputation is used to restore the ancilla bits to the OFF state before finishing.

Uncomputation is a technique, used in reversible circuits, for cleaning up temporary side effects on ancilla bits so they can be re-used.[1]

Uncomputation is important to quantum computing. Whether or not intermediate effects have been uncomputed affects how states interfere with each other when measuring results.[2]


  1. ^ Aaronson, Scott; Grier, Daniel; Schaeffer, Luke (2015). "The Classification of Reversible Bit Operations". arXiv:1504.05155 [quant-ph].
  2. ^ Aaronson, Scott (2002). "Quantum Lower Bound for Recursive Fourier Sampling". Quantum Information and Computation ():, 00. 3 (2): 165–174. arXiv:quant-ph/0209060. Bibcode:2002quant.ph..9060A.