2.concept课件.ppt

Quantum Concept  2009.03.16;Good question;outline;;Quantum concept;Information theory;经典信息论;量子信息论;Claasical and quantum;Quantum concept---a qubit;basis;Examples:;Quantum concept—qubit ;;Multiple qubits- two qubit system;eg;Multiple qubits;;;;Quantum State Measurement Measurement changes the state of a qubit, collapsing it from its superposition of |0 and |1. The measurement of a qubit will give only either 0 or 1. Why does this type of collapse occur? Nobody knows! This behavior is simply one of the fundamental postulates of quantum mechanics.;Postulate 3: Quantum measurements are described by a collection of measurement operators. These are operators acting on the state space of the system being measured. The index refers to The measurement outcomes that may occur in the experiment. If the state of the quantum system is immediately before the measurement, then the probability of result is given by and the state of the system after the measurement is The measurement operators satisfy;量子测量假设： 量子测量由一组测量算子描述，这些算子作用在被测系统状态空间上且测量后系统的状态满足概率为1的事实，即测量算子满足完备性方程。 ;From a single measurement one obtains only a single bit of information about the state of qubit.;测量会改变量子状态，从叠加态坍缩到特定状态。 这是量子力学的基本原理之一。 　对于量子比特的一次测量，只得到有关量子比特状态的一比特信息。 那么，如何确定量子比特的状态呢？ 事实上： 只有测量无穷多完全相同的量子比特才能确定;Multiple qubits- two qubit system;Multiple qubits-two qubit system;;;;1. Quantum Logic Gate;Quantum computation;Quantum computation;A singal bit logic gate;X;eg;昏阻椎阜气汰智孔馒脾生椭子砌陌砸垃酣淳答汕扔挛粱票蜂箱绽鄙腥式膛2.concept课件2.concept课件;多量子比特门;Controlled NOT (CNOT);Multiple qubit gates;多量子比特门;Multiple qubit gates;经典NAND(与非门) 对应着一个量子酉门吗？ 不! 经典NAND(与非门)具有本质的 不可逆性。 这种不可逆性带来了信息的损失。;No-cloning theroem;Example Operation - Multiplication By 2 ;; (1)Basic model for quantum algorithm The algorithm on classical computer may not be reversible transformation, but it should be reversible on quantum computer. Therefore, we should transfer cl