ancilla

plural ancillae

1. rareA maid.

   ‘And pass me that towel,’ added Ada, but the ancilla was picking up coins she had dropped in her haste […]

   1969, Vladimir Nabokov, Ada or Ardor, Penguin, published 2011, page 306

2. An auxiliary or accessory.

   The filter achieves this two-qubit filtering effect by using two ancilla photons as probes that detect whether or not the two input photons are in the desired states.

   2009 January 23, Ryo Okamoto et al., “An Entanglement Filter”, in Science, volume 323, number 5913, →DOI

3. computingAn ancilla bit.

   The circuit uses a single ancilla for each stabilizer generator.