▁about ▁L 2 ▁or ▁about ▁ 1 0 7 ▁steps ▁and ▁at ▁ 1   M Hz , ▁about ▁ 1 0 ▁seconds . ▁ ▁A ▁very ▁different ▁approach ▁to ▁the ▁stability - de co her ence ▁problem ▁is ▁to ▁create ▁a ▁topological ▁quantum ▁computer ▁with ▁any ons , ▁quasi - part icles ▁used ▁as ▁threads ▁and ▁re lying ▁on ▁bra id ▁theory ▁to ▁form ▁stable ▁logic ▁gates . ▁ ▁Phys ic ist ▁Mik h ail ▁Dy ak on ov ▁has ▁expressed ▁ske ptic ism ▁of ▁quantum ▁computing ▁as ▁follows : ▁" So ▁the ▁number ▁of ▁continuous ▁parameters ▁describing ▁the ▁state ▁of ▁such ▁a ▁useful ▁quantum ▁computer ▁at ▁any ▁given ▁moment ▁must ▁be ... ▁about ▁ 1 0 3 0 0 ... ▁Could ▁we ▁ever ▁learn ▁to ▁control ▁the ▁more ▁than ▁ 1 0 3 0 0 ▁continu ously ▁variable ▁parameters ▁defining ▁the ▁quantum ▁state ▁of ▁such ▁a ▁system ? ▁My ▁answer ▁is ▁simple . ▁No , ▁never ." ▁ ▁Develop ments ▁ ▁Quant um ▁computing ▁models ▁ ▁There ▁are ▁a ▁number ▁of ▁quantum ▁computing ▁models , ▁distinguished ▁by ▁the ▁basic ▁elements ▁in ▁which ▁the ▁computation ▁is ▁decom posed . ▁The ▁four ▁main ▁models ▁of ▁practical ▁importance ▁are : ▁ ▁Quant um ▁gate ▁array ▁( comput ation ▁decom posed ▁into ▁a ▁sequence ▁of ▁few - qu bit ▁quantum ▁gates ) ▁ ▁One - way ▁quantum ▁computer ▁( comput ation ▁decom posed ▁into ▁a ▁sequence ▁of ▁one - qu bit ▁measurements ▁applied ▁to ▁a ▁highly ▁ent ang led ▁initial ▁state ▁or ▁cluster ▁state )