. ▁Ex amples ▁include ▁the ▁quantum ▁gates , ▁and ▁the ▁lattice ▁v ibr ations ▁and ▁background ▁therm on uc lear ▁spin ▁of ▁the ▁physical ▁system ▁used ▁to ▁implement ▁the ▁qu bits . ▁Dec oh er ence ▁is ▁irre vers ible , ▁as ▁it ▁is ▁effectively ▁non - unit ary , ▁and ▁is ▁usually ▁something ▁that ▁should ▁be ▁highly ▁controlled , ▁if ▁not ▁avoided . ▁Dec oh er ence ▁times ▁for ▁candidate ▁systems ▁in ▁particular , ▁the ▁trans verse ▁relax ation ▁time ▁T 2 ▁( for ▁N MR ▁and ▁M RI ▁technology , ▁also ▁called ▁the ▁de ph asing ▁time ), ▁typically ▁range ▁between ▁nan ose cond s ▁and ▁seconds ▁at ▁low ▁temperature . ▁Currently , ▁some ▁quantum ▁computers ▁require ▁their ▁qu bits ▁to ▁be ▁co o led ▁to ▁ 2 0 ▁mill ikel v ins ▁in ▁order ▁to ▁prevent ▁significant ▁de co her ence . ▁ ▁As ▁a ▁result , ▁time - consum ing ▁tasks ▁may ▁render ▁some ▁quantum ▁algorithms ▁in oper able , ▁as ▁maintain ing ▁the ▁state ▁of ▁qu bits ▁for ▁a ▁long ▁enough ▁duration ▁will ▁eventually ▁cor rupt ▁the ▁super pos itions . ▁ ▁These ▁issues ▁are ▁more ▁difficult ▁for ▁optical ▁approaches ▁as ▁the ▁times cal es ▁are ▁orders ▁of ▁magnitude ▁shorter ▁and ▁an ▁often - c ited ▁approach ▁to ▁over coming ▁them ▁is ▁optical ▁pul se ▁sh aping . ▁Error ▁rates ▁are ▁typically ▁proportional ▁to ▁the ▁ratio ▁of ▁operating ▁time ▁to ▁de co her ence ▁time , ▁hence ▁any ▁operation ▁must ▁be ▁completed ▁much ▁more ▁quickly ▁than ▁the ▁de