Processing and Transmission of Quantum Information

量子信息由量子位而不是位组成。量子位是一个两能级的量子系统，其中能级代表0和1。与经典比特不同的是，它可以以0和1的叠加态存在，这一特性使得新型的信息处理成为可能。提出的应用包括量子密码学、超密编码和量子计算。量子位可以被设备当作量子门来处理。通用量子器件的性能不依赖于输入状态。一个已经被研究过的例子是量子复印机，它产生两个输入量子比特的不完美副本。其他通用装置有通用非门、通用纠缠器、通用解纠缠器和通用转座器。所有这些设备都应该相对简单，并且能够通过少量量子门来实现。多能级和连续系统也可以用来表示量子信息。压缩态可以用作量子密码协议的基础，这将允许使用放大器来克服传输损耗。

Quantum information consists of qubits rather than bits. A qubit is a two-level quantum system where the levels represent 0 and 1. Unlike a classical bit, it can exist in a superposition of 0 and 1, and this property makes novel kinds of information processing possible. Proposed applications are quantum cryptography, superdense coding, and quantum computing. Qubits can be processed by devices as a quantum gates. A universal quantum device is one whose performance does not depend on the input state. An example, which has all ready been studied, is a quantum copier, which produces two imperfect copies of an input qubit. Other universal devices are a universal NOT gate, a universal entangler, a universal disentangler, and a universal transposer. All of these devices should be relatively simple and able to be realized by a small number of quantum gates. Multilevel and continuous systems can also be used to represent quantum information. Squeezed states can be used as the basis of quantum cryptographic protocol which would allow amplifiers to be used to overcome transmission losses.