Quantum computing
Quantum computing
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DOI：
10.1073/pnas.95.19.11032
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发表时间：
1998-09-15
影响因子：
11.1
通讯作者：
Monroe, C
中科院分区：
文献类型：
--
作者：
Brassard, G;Chuang, I;Monroe, C
量子计算是经典计算到量子信息处理的扩展，使用诸如单个原子、分子或光子的量子系统。它有可能在计算机科学领域带来一场壮观的革命。当今的电子计算机与纯粹的机械计算机没有根本的不同：两者的操作都可以完全用经典物理学来描述。相比之下，计算机原则上可以从真正的量子现象中获益，这些现象没有经典的类似物，例如纠缠和干涉，有时与经典计算机相比可以提供指数级的速度。量子信息。所有的计算机都在操纵信息，而量子信息的单位是量子比特。经典比特可以取0或1，但量子比特可以是两个经典状态的线性叠加。如果我们用0和1来表示经典比特，那么量子比特可以处于任何状态0 1，其中和是复数，称为幅度服从2 2 1。任何测量量子位的尝试都会引起不可逆的扰动。例如，对0 1的最直接测量导致量子比特做出概率决定：概率为2，它变成0，互补概率为2，它变成1;在任何一种情况下，测量设备都告诉我们采取了哪种选择，但所有先前的原始振幅记忆都丢失了。与经典比特不同，n个0和1的单个字符串足以描述n个比特的状态，n个量子比特的物理系统需要2n个复数来描述其状态。例如，对于任意复数、、，两个量子位可以处于状态00 01 10 11，并且仅受约束2 2 2 1。量子比特的另一个特征是纠缠特性。考虑两个量子比特状态（00 01 10 11）2。这种状态比实际看起来要简单，因为它可以分解为两个单量子比特状态的乘积，每个状态都是（0 1）2。类似地，许多n量子比特状态可以以因子化的形式写入，因此只需要2n个数字来描述它们，这比通常需要的2n个数字少得多。然而，一些特殊的状态，如（01 10）2不能被分解。当测量这两个量子比特时，它们产生0和1或1和0，具有相等的概率（12）2 12，但是直到实际执行测量才确定这两个结果中的哪一个。这没有经典的类比。量子计算依靠纠缠量子信息蓬勃发展的计算机可以比经典计算机运行得更快，因为n个量子位需要2n个数字来描述。对这些量子比特的一些简单操作可以通过使用量子并行和量子干涉来影响所有2n个数字。
Quantum computation is the extension of classical computation to the processing of quantum information, using quantum systems such as individual atoms, molecules, or photons. It has the potential to bring about a spectacular revolution in computer science. Current-day electronic computers are not fundamentally different from purely mechanical computers: the operation of either can be described completely in terms of classical physics. By contrast, computers could in principle be built to profit from genuine quantum phenomena that have no classical analogue, such as entanglement and interference, sometimes providing exponential speed-up compared with classical computers.Quantum Information. All computers manipulate information, and the unit of quantum information is the quantum bit, or qubit. Classical bits can take either value 0 or 1, but qubits can be in a linear superposition of the two classical states. If we denote the classical bits by 0 and 1, a quantum bit can be in any state 0 1, where and are complex numbers called amplitudes subject to 2 2 1. Any attempt at measuring qubits induces an irreversible disturbance. For example, the most direct measurement on 0 1 results in the qubit making a probabilistic decision: with probability 2, it becomes 0 and with complementary probability 2, it becomes 1; in either case the measurement apparatus tells us which choice has been taken, but all previous memory of the original amplitudes and is lost. Unlike classical bits, where a single string of n zeros and ones suffices to describe the state of n bits, a physical system of n qubits requires 2n complex numbers to describe its state. For example, two qubits can be in the state 00 01 10 11 for arbitrary complex numbers,,, and subject only to the constraint 2 2 2 2 1. Another feature of qubits is the property of entanglement. Consider the two-qubit state (00 01 10 11) 2. This state is less complicated than it actually looks, because it can be factored into the product of two one-qubit states, each of which is (0 1) 2. Similarly, many n-qubit states can be written in factored form and thus require only 2n numbers for their description, which is much less than the 2n numbers generally required. However, some special states such as (01 10) 2 cannot be factored. When these two qubits are measured, they yield either 0 and 1 or 1 and 0, with equal probability (12) 2 12, but which of these two outcomes will occur is not determined until the measurement is actually performed. This has no classical analogue. Quantum Computing. Computers that thrive on entangled quantum information could run exponentially faster than classical computers because n qubits require 2n numbers for their description. A few simple operations on these qubits can affect all 2n numbers through the use of quantum parallelism and quantum interference.