A brief introduction to Quantum computer Alri

Moore's law the number of transistors in a dense integrated circuit has doubled approximately every two years ——- Gordon E. Moore, the co-founder of Intel 晶体管

speed and computing capacity

physical limits atomic level

quantum theory

classical computer ——> quantum computer?

two-state quantum-mechanical system Qubit a linear superposition of basis states both states at the same time two-state quantum-mechanical system 量子比特，线性 叠加态

Quantum entanglement system as a whole one particle of an entangled pair "knows" what measurement has been performed on the other, and with what outcome

Faster-than-light Quantum mechanics not true communication two observers in different locations see the same system simultaneously

Energy and computing Landauer's principle: the erasure of n bits of information must always incur a cost of n k T ln(2) in thermodynamic entropy erasure of information — necessary?

Reversible computing the relation of the mapping from states to their successors must be one-to-one

Toffoli gate CCNOT gate "controlled-controlled-not" gate any reversible circuit can be constructed from Toffoli gates 3-bit inputs and outputs : if the first two bits are set, it inverts the third bit, otherwise all bits stay the same

(a,b,c)=Toffoli(Toffoli(a,b,c)) Toffoli gate The Toffoli gate is reversible (but the Toffoli' used above is not). This means that any computation did with it can be undone. This is: (a,b,c)=Toffoli(Toffoli(a,b,c))

Universality and Toffoli gate Boolean functions： OR, AND，NOT gates NOR gates NAND gates 若知道一个封闭物理系统的最终状态，则可以求出该系统的最初状态，这样导致在不擦除信息的前提下可进行计算

Toffoli gate NAND(a,b)=Toffoli′(a,b,1) NOT(x)=Toffoli′(1,1,x)

basic quantum computers that can perform certain calculations

D-Wave Systems 512-qubit D-Wave Two quantum computer 1000万美元

new era

References https://en.wikipedia.org/wiki/Moore%27s_law https://en.wikipedia.org/wiki/Qubit#Bit_versus_qubit https://en.wikipedia.org/wiki/Quantum_entanglemen t http://www.technologyreview.com/view/422511/th e-fantastical-promise-of-reversible-computing/ https://en.wikipedia.org/wiki/Toffoli_gate http://www.dwavesys.com/quantum-computing

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