There is a fun simulation on Quantum Encryption that you can use (it requires Flash, but no special math!) - click here


This is the premise of the simulation: Alice and Bob want to exchange a secret key like a number written in binary code – i.e. a series of 0 and 1. If they would use classical methods, Eve could try to snoop in and listen to the signal that is being exchanged. However, if Alice and Bob use entangled particles to transmit their key they could always check if Eve is snooping. We will first play with the simulation and then explain further how the secret key can actually be exchanged. 


The simulation measures the spin of a particle using magnets with two different orientations Z and X. Translated in the language we have used in Lesson 13, this is equivalent with saying that for orientation Z you are measuring the "color" of a particle, and for orientation X you are measuring its "flavor". Or, translated in the language we have used in Lesson 14, orientation Z corresponds to Setting 1 and orientation X corresponds to Setting 2. The only difference is that in this simulation the pair of particles will always go in opposite directions when measured with the same detector (up-down, down-up).

模拟用两个不同方向的z和x来测量粒子的自旋,用第13课中所用的语言翻译,这相当于说,对于方位Z,你测量的是粒子的“颜色”,而方位x,你在测量它的“味道”。或者,用我们在第14课中使用的语言翻译,方向Z对应于设置1,方向x对应于设置2。唯一的区别是,在这个模拟中,当同一个探测器(向上、向下)测量时,这对粒子总是朝相反的方向移动。The Simulation has its own Step-by-Step explanation, but we recommend this order of interaction: 


1. Press Show Control; From "Display Controls" check all the three options

1. 按下显示控件;从“显示控件”检查所有三个选项

2. Choose "Fixed Orientation" and make sure both magnets have the same orientation (X-X or Z-Z). Send a few single particle pairs. You will notice that the results of Alice and Bob are always coordinated 1-0 or 0-1. If Bob inverts his value he will get Alice's value. 

2. 选择“定位”,确保磁体具有相同的取向(X-X或Z-Z)。发几单粒子对。你会注意到爱丽丝和鲍伯的结果总是协调1-0或0-1。如果鲍伯将他的值键入,他会得到爱丽丝的值。

2'. Change the orientation of one of the magnets such that one has Z and the other X. Send a few single particle pairs. You will notice that now all outcomes are possible: Alice 0 – Bob 0; Alice 0 – Bob 1; Alice 1 – Bob 0; Alice 1 – Bob 1. In this case Bob cannot make any inference about Alice's code.

 2’. 改变一个磁体的方向,使其具有z和其他x。你会注意到现在所有的结果都是可能的:爱丽丝0 -鲍勃0;爱丽丝0 -鲍勃1;爱丽丝1 -鲍勃0;爱丽丝1 -鲍勃1。在这种情况下,鲍伯不能对爱丽丝的代码作出任何推论。