Quantum Computer ( その他趣味 ) - 自由な談話室

Quantum Computer

Quantum physics is one of the most weird studies in 20th century. It is a study about very
small particles like photons which are the smallest composition of light, and it often
contradicts the common sense of physics, but its curious aspects give us much inspiration.
Why is the study revolutionary?

Curious properties of the photon
・Light is famous for its dual properties: the wave and particle. These don’t appear at the
same time, so an experiment that can detect the wave properties can’t detect the particle one
and vice versa. I’d like to explain an example of each. When light passes through the two slits in a wall, each light interferes in the other one, as a result these form one wave like the sea wave.
When light reflects from one kind of metals, it seems brighter than reflection from the another materials. The higher photons’ energy is, the brighter the reflection is. Even though
more waves impinge on the metals, the brightness of the reflection doesn’t change (Imagine a billiard ball.) This shows that the light behaves not only as a particle but also as a wave.
A physicist conducted an experiment to show that the light is a particle and the wave is produced by each particle’s interference. The experiment is to make a device to emit only one photon at a time and direct it go through two slits. If the light were a particle, its path would be straight and no wave would be made. However the result was counterintuitive. It behaved like wave furthermore its path was unpredictable. (I don’t write about it in detail but it is enough to know that the photon has such a property in this article.)

Many worlds interpretation
・David Deutsch, a famous physicist, tried to explain like this;“The wave is made by the
interference of particles so there must be a shadow particle. I concluded that a particle in the another world interferes with the particle in our world.” It sounds very weird but it is hard to disprove. There is a specific experiment known as Schoerdinger’s Cat that must puzzle you.
1 A cat is confined in a box.

2 There is a device in the side of the box which has two slits and emits the poison gas.

3 The trigger of it is a photon. If the photon went through the slit above the device, it emits gas, otherwise it doesn’t.

It depends on the photon whether the cat will die or not. It behaves unpredictably, so we can’t know the cat die or not until we open the box. However, it is weird. The fact was already decided, but we just don’t know it. If the fact decided by our observation, the cat is neither alive or dead? Deutsch explains “There are two worlds, so our exsintence doesn’t influence the result.” Compared to other explanations, it is advantaged in the economy with postulates.

Quantum computer
・It remains to be answered whether Deutsch is right or not, but technology is improving.
A quantum computer is one of them. I’d like to explain it by using Deutsch’s theory. If a
quantum which has two modes were used as a part of the processor, it can process two
programs at the same time. Imagine making a computer to find out premiums from 1 to 1000.
Pentium processor starts from 1, but the start point is only one. On the other hand, a quantum processor can have many modes, so it can start from a lot of points. First from 1 to
100, second from 100 to 200…. If ten quantum were used, it can process 1024 programs
simultaneously. The RSA system code which a usual computer takes more than 1trillion years
to decipher can be broken within 1 year by a quantum computer. In addition to that, it can
make the ultimate cipher by using its unpredictability. What do you think about quantum
technology? Is it a devil technology or the Messiah?