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密碼學(xué)中的state是什么意思( 四 )

云知道密碼


光放大器的意思是如果你輸入一個(gè)非常弱的信號(hào)
例如一個(gè)單光子
有時(shí)它會(huì)被放大，但有時(shí)不會(huì)被放大
所以你會(huì)得到一個(gè)與它一起輸出的噪聲光子
所以，光束會(huì)變得更亮
但是在分辨光子偏振上 ， 與原始未放大光子相比
亮光束不會(huì)更有用
因此沒(méi)有辦法解決這個(gè)不確定原則
——The end——
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英文版
So I'm going to be talking about the relation of physics to mathematics also.
But what I'd like to do is take an area of mathematics or physics,
which is considered to be really hard to understand, worse than rocket science.
And give you some tools for understanding it
if you're not a technically minded person.
Or if you are a technically minded person,
some metaphors are ways of explaining it to the general public.
Because I think the non understanding of quantum physics,
which is now lies at the root of information and communication,
is a terrible thing to not understand.
It's one of the fundamental things about the universe that we live in
that everyone should understand, not just scientists.
And that means that we need to find the right ways of explaining it.
We're in the middle of an information revolution.
This revolution is based on some really brilliant abstractions by many people.
But we associate them with Turing,
who put the theory of computing into an abstract basis,that is
that you can think about computing is independent of the notion of thehardware.
There is a universal notion of computing.
There is a universal computer that can simulate any other computer.
And Shannon,
who did something even more revolutionary,
that is to think about communication in an entirely mathematical way.
That is that there is a theory of communication.
that is independent of the meaning of the message.
Now,even today, if you try to say to a person on the street,
"I want to tell you about communication without telling you about meaning."
they would think you were a little crazy.
And yet that's what leads to the information revolution we had today.
But the information carriers, Turing and Shannon thought about, were viewed
as what a physicist would call a classical system.
And that is that their statesare in principle reliably distinguishable,
and are not disturbed by measuring them.
Youcan make a copy of information.
In fact, you can do it very easily.
And the only kind of trouble you can get into is a typically legal trouble.
Tospecify the joint state of two things,
it's necessary and sufficient to say the state of each one.
That almost goes without saying.
Well,anyway, physicists and chemists have known for a long time,
that atoms and small particles like atoms andphotons don't really behave that way.
But that was a matter of interest, really only for physicists and chemists.
And now we know that these last properties here
are important not only for physics and chemistry,
butfor understanding what information and communication are all about.
In other words, what Shannon and Turing should be thinking about.
Nowadays,everybody understands classical information,
cause we use it all the time.
If you go to a computer store and you say,
"Do you have that program for my mac?"
You're in principle, using the idea of Turing and there is a universal computer.

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