Quit nd Quntum Gtes Shool on Quntum omputing @Ygmi Dy, Lesson 9:-:, Mrh, 5 Eisuke Ae Deprtment of Applied Physis nd Physio-Informtis, nd REST-JST, Keio University
From lssil to quntum Informtion is physil - Rolf Lnduer QUANTUM informtion or quntum INFORMATION? It depends on your kground physis or informtion siene Ultimtely, you need oth At the eginning, it would e etter to keep one perspetive physis here
Referenes Quntum omputtion nd Quntum Informtion nd referenes therein, M. A. Nielsen nd I. L. hung, mridge University Press Dy, Lesson - Dy, Lesson Physil Review A 65, 3, N. D. Mermin Dy, Lesson L. M. K. Vndersypen, Ph. D Thesis ville t riv: qunt-ph/593 Dy, Lesson
Outline Rules of the gme Quntum it Stte spe Quntum gte Unitry evolution NOT, Y,, Hdmrd H Mesurement Multiple-quit Tensor produt NOT, SWAP, ontrolled-, Toffoli
Quntum it For physiists, quntum it quit is synonym for quntum mehnil two-level system g e Superposition
Quntum it Vetor nottion for omputtionl sis sttes POSTULATE ψ α β α α β α, β : Proility mplitude Stte spe Hilert spe β : Proilities sum to
Unitry evolution POSTULATE The evolution of quit system is desried y unitry trnsformtion suh s ψ t U ψ t Hermitin onjugte: A A T * Hermitin self-djoint: A A Unitry: UU I d * * d * *
Unitry evolution ih d ψ onnetion with the Shrödinger eqution dt H ψ H: Hmiltonin of the quit system Hermitin ih t t ψ t exp ψ t U ψ t h Exponentil opertor unitry Any unitry opertor U n e relized in the form U expih where H is some Hermitin opertor For now, tul physil systems tht relize neessry Hmiltonins re NOT our interest
Quntum gte ψ t U ψ t Input U Output ψ t ψ t Suessive implementtion Time L ψ ψ U U U 3 U n U ψ U U ψ Time U LU U n ψ
Quntum gte Input ψ α β Output U U ψ U α β We hve infinite inputs, ut it suffies to onsider only the omputtionl sis sttes U U Superposition priniple U α U β U U ψ U U
NOT gte lssil NOT Input output Quntum NOT The only non-trivil one-it gte in the lssil se or Mtrix representtion
Mtrix representtion The first olumn represents the finl stte of The seond olumn represents the finl stte of
Puli-, Y, gtes i i Y i Y i Y Y i iy i Y i Y Y Y ], [ ], [ ], [ I Y }, { }, { }, { Y Y Hermitin ommuttion reltions
Hdmrd gte, H,,, H H H H H HH Y HYH HH H I Hermitin iruit identities
Mesurement gte POSTULATE ψ α β Quntum it lssil it Mthemtil desription Generl mesurement Projetive mesurement POVM with proility α, or with proility β
Multiple-quit How do we desrie multiple-quit sttes? omputtionl sis sttes for two-quit sttes my e written s,,, We require them to e orthogonl, so they my e written s Speultion A multiple-quit stte is the tensor produt of the omponent quit systems POSTULATE
Tensor produt omputtionl sis set for -quit sttes Mtrix representtion
Multiple-quit gtes 3 U U 3 L n M M n n : n -dimensionl vetor U : n y n unitry mtrix
Independent gtes H H Y H H Y YH H H YH H YH U 8 y 8 unitry mtrix 4 4 4 4 3 4 4 3 4 3 3 4 3 3 3 3 4 3 4 3 4 3 B B B B B A
ontrolled-u gtes ontrol it if Trget it U U U if U n e n ritrry single-quit gte U works only when U is just forml expression
NOT gte if if,,, Frequently used
NOT gte,,, Never mistke
SWAP gte SWAP 3 4 To implement SWAP, we need to. Enode informtion on into nd quit. Erse informtion on from st quit 3. Enode informtion on into st quit 4. Erse informtion on from nd quit
ontrolled- gte ontrolled- is nonlol
Toffoli Toffoli Toffoli is often referred to s ontrolled-ontrolled-not -NOT
Quiz Prove the following iruit identity Also prove the followings H I HH Use the following expressions for quntum gtes H,
Answer 3 3 sde implementtion sde ersure
Answer H HH onstrutive nd destrutive interferenes
Answer H H HH onstrutive nd destrutive interferenes