
English: 
In classical digital computers, we know that
it is possible to implement any logic operation
by using a combination of NOT gates on a single
bit and negative-AND gates on pairs of bits.
A similar situation exists in quantum computing
but with a very important difference.
Not all the classical logic gates are allowed in the quantum world.
This is because quantum mechanics imposes very stringent requirements.
A quantum system can never lose information over time and it must always be possible to reconstruct the past.
Let's take the example of the AND logic operation.
It takes two inputs and gives one output with the value one if and only if both inputs are one.
Obviously, I have no way to tell what the two input bits were just by looking at the one bit output.
So let's say that I let one of the inputs propagate and change to the output.

Chinese: 
传统的数字计算机是能够运行
任意的逻辑运算指令的
这是通过使用一位非门和
二位与门的组合实现的
量子计算机与其有异曲同工之处，
但是又与众不同
并不是所有的逻辑门都适用于量子世界中
这是因为量子力学遵守非常严格的要求
量子系统中从未因时间的流逝而丢失过信息，
量子系统必须随时重现初始信息
以与门逻辑操作为例
与门操作过程是每两个输入值会得到一个输出值，
当且仅当两个输入值均为1时，输出值才为1
很显然，我不能通过一位输出值得知具体的两个输入值
所以我们将其中一个输入值视为另一个输出值

English: 
Even with these two bits of information at the output
there is still an ambiguity that prevents me from reconstructing the past.
The output 00 could arise from inputs 00 or 01. In the quantum world, this would not be allowed.
So let me show you a logic gate that is allowed in the quantum world.
We call it CNOT gate which stands for Controlled-Not.
It applies a NOT operation to qubit B when qubit A is in state one.
If qubit A is 0, qubit B is left unchanged.
If qubit A is 1, qubit B gets flipped.
Now you see that there is no ambiguity.
There are four different possible outputs, each corresponding to four different inputs which I can reconstruct knowing the outputs.
No information is lost. If the qubits are physically implemented with spins, creating a CNOT gate is very simple.
The frequency at which Spin B responds to an electromagnetic field depends on the state of Spin A in its vicinity

Chinese: 
尽管现在有两位输出值
但是对于原始输入值的信息仍不明确
输入值是00或01都可以得到输出值为00的结果
然而，量子世界中不存在这种状况
因此我要为大家介绍一下量子世界中存在的逻辑门
我们通常说的CNOT逻辑门指的是受控反闸
这应用于量子比特A处于特定状态，
量子比特B执行非操作的时候
如果量子比特A数值为0，那么量子比特B数值不变
如果量子比特A数值为1，那么量子比特B数值会
发生相对改变（即0变1，1变0）
现在你会发现一切都是一目了然的
共有四组不同的输出值，依据每组的
输出值可以得出具体的输入值
没有信息丢失
如果量子比特是自旋粒子，那么
要实现受控反闸就很简单了
自旋粒子B的频率反应了自旋粒子A
周围电磁场的状态

Chinese: 
因为自旋粒子A产生了由其旋转方向决定的磁场
因此，自旋粒子A可以控制自旋粒子B
是否发生数值的相对改变
受控反闸可以使量子A、B处于量子纠缠态
假定量子A设定为0和1的态叠加
量子B设定为受控反闸，
量子A、B一起任意旋转
受控反闸就是这样应用于量子
计算机的任意逻辑功能中的
我们刚刚在一直探寻构建
量子计算机需要什么
我们需要单独、可以任意方向
旋转的量子比特
也需要几组可以执行受控反闸、
产生互相作用的量子比特
字幕由澳大利亚新南威尔士大学翻译专业王梦晨制作。

English: 
because Spin A produces a magnetic field that depends on its orientation.
Therefore, Spin A controls whether I can flip Spin B.
The CNOT gate can be used to produce an entangled state of A and B.
We just have to prepare A in the super position of 0 and 1
and then apply a CNOT to B, together with arbitrary single qubit rotations,
the CNOT gate can implement any logic function on a quantum computer.
So we are starting to see what it takes to build a quantum computer.
We need individual qubits that we can rotate in arbitrary directions
and we need interactions between pairs of qubits that implement CNOT gates.
