Re: quantum computing

[Aiviet Nguyen <aiviet@cat.syr.edu>]

Hi Thu Huong and Van,
  The explanation of THu Huong sounds like the popular articles in NY Times.
It would be OK if you can live with that. But actually that is not the real
situation.
  There is no relation with 
     electron=slower=bigger
     photon = faster= smaller
in quantum computing.
  
   There are two issues in computing: storage and processing.
The unit of infomation in the ordinary computing is a bit, while in QC it 
is a q-bit. If a bit is a state that can have two values 1 and 0, a q-bit is
a linear combination ( superposition of that) of two values:
             \Psi = a |0> + b |1>
So if you use q-bit then you can store more information.

  In fact, you store a bit in a magnetic domain or in a register. Now the 
q-bit can be stored in any quantum state of some quantum system. It can 
be a spin in general, but for technical reason they can realize it only 
in spin glass. ( an electron, a photon and an atom maybe better as they 
are small, but the trade-of is that you cannot keep this data for a long 
enough time and measure the spin of one single quanta)

  In fact N q-bits can be represented by exp(N) digital bits. That means
the algorithms that are exponential ( unsolvable) can be finite and 
solvable in QC. So the processing is also faster.

  The main issue of QC is how to isolate the quantum states from the 
environment. The Quantum mechanics says that any quantum state evolute by 
time. Recently there are few success on this field by new technologies.
However, QC is still far from being practical.
 
  I just described very briefly and in a very layman language. Let me 
know if you want more technical explanation.

Cheers
Aiviet 


   

On Wed, 9 Apr 1997, Ha Van Vu wrote:

> Dear Thu Huong,
> 
> Thanks for the reply. I remember someone tried to explain 
> quantum computers to me and mentioned that it uses the superpositions of
> particals (the number of superpositition is large). Therefore the computer
> can do many operations at the same time.
> 
> How does it fit into your explanation ? I guess you may say the same thing by another way.
> 
> Best, Van
>