Logic gates and illogic thrusts in quantum computing.

Quantum computer is probably the most prominent subject of quantum physics. Reason is obvious. While all the mystifying test results in quantum mechanics only seem to bug people's minds, quantum computers would put all this confusing potential to maximum benefit. Increasing endeavor to produce quantum computers has already grasped mainstream public attention, which is not very commonplace situation for futuristic technology. Even some people who don't have any particular interest in physics may have heard of qcs and started to adapt the idea. This may result less than usual resistance towards this new technology once it appears.

Early acceptance towards qc would be beneficial to everyone.*

Computers we use today speed up almost constant rate. In the progress bulgy relays has transformed to notably large vacuum tubes to sole transistors and to integrated circuits holding many transistors in a single chip. And while still integrated circuits are the building bricks of modern computers, Moore's law has pretty accurately predicted that amount of transistors on integrated circuits doubles every two year. Key feature to achieve this has been the size. Technology manufacturers has been able to miniaturize transistors so that more and of them will fit into single chip. This very handsome trend has unfortunately limits however, one of the most obvious one is that when transistor reaches size of an atom it cannot be divided into smaller pieces. More likely that small transistors won't be ever be achieved, because when the quantum rules begins to place in the small realm of tiniest chipsets, whole new formation of rules and phenomenons are required to be considered in the manufacturing process.

Classical transistors themselves act as logic gates in computer chips. Logic gates are like small counters who can count to two using Boolean algebra. Well, to tell difference between values 0 and 1 to be accurate. These values could represent basically any physical property that can be measured, voltage of electrical current for example (≥5V = 0; 7V≥= 1). There are many different kind of gates available, but ordinary computer doesn't have to have all of them in order to be universal (universal means it can compute any possible binary code). Quantum computers would have to have major difference in it's logic gates, since data wouldn't be processed in any certain state using quantum bits (quantum bits = qubits I mentioned in my previous text).

AND logic gate's and NOT gate's truth tables. AND gives out 1 if both inputs are 1, otherwise it gives 0. NOT gate always changes input, therefore it is common called inverter.

Notice how you could guess what was the input in NOT-gate if you knew only output? Well same is not with AND-gate. You cannot tell if A or B both were 0 or if only one of them was 1 if output is 0 You loose some information when you move from input to output. Logic gates in quantum computing would have this thing differently and it's one the reasons why theoretically qc is faster than ordinary computer. However it would be faster only in some processes and not so smooth in others. Much like an airplane is faster so long as it stays airborne.

Early qc pioneer Edward Fredkin came up with idea for logic gate for qc. Fredkin had a dream of building a reversible computer and he realized that this can be achieved if no information is lost in a logic gate. Truth table in Fredkin gate looks confusing at first, put if you pay attention to it, you'll notice that c value never changes when it move trough the gate. Also notice other two values p and q don't change when c = 0, and they switch places if c=1. Fredkin gate is universal and completely reversible.

Fredkins gate is an example of logic gate in quantum computer.

When I wrote Fredkins gate is reversible, it means that it can undone itself without consuming resources. This is not possible with ordinary transistors. However if qc is build to use physical properties that are entangled, like spin or polarization, it is possible to have logic gates that puts spooky action at a distance into better use than confusing Einstein. Swapping from input to output and from output to input without consuming time or energy, quantum computer could provide answers to questions which are presently thought to be unsolvable, thrusting mankind's capabilities into new highs, beyond quantum barriers which seem to separate our world from another, smaller, but more potential one. 

2>2 or: How I Learned to Stop Waiting and Love the Computer

The fuss on quantum computing has been quite excessive considering it has been going on for almost 40 years now. Quantum computer (qc) has been accepted as a likely future innovation around in the 80's and has been expected to pop up sooner or later since that. Early pioners of qcs were pretty much living in the blind spot of the scientific community, until Richard Feynman got interested in the qcs. He had already that point won a Nobel price and was altogether very influential scientist, so he was able to raise the general interest in the qcs in hes speech in MIT - conference.

What would it do then?

Whole concept of quantum type of information technology is staggering all the way beyond the imaginable. Scientist have made such promises about qc that they would change the world at once and for good. Back to the title of this post. One may ask: What could quantum computing possibly offer if it uses basically same binary code than in ordinary Turing machine? Line of zeros and ones. The thing is that they are not the same numbers 0 and 1 since the code would the superposition of each other. Quantum bit is actually called qubit for that. Since the line of code would be in the superposition of all the other possible lines of code, this qc would answer all the possible variations of questions simultaneously. On the contrary classical computer could have to done that same thing, but time consumingly.

First commercially successful quantum computer might look like this.
Shuttle at The Intrepid Sea, Air & Space Museum, New York.

The fun part of waiting these quantum computers is that nobody can't predict what the first truly successful qc looks like, or what technique it uses to produce qubits. The thing is that quantum mechanics provide numerous of ways to produce qubits. Basically any physical property that can be in superposition could be used to simulate qubits. So first Quantum-pc could have mirrors and lights and qubit would be the superposition of photon polarization. Or it could be using spin of a electron or why not spin of a nuclei. Several other possibilities is already know today.

Taking into consideration numerous ways to build a qc, and the time that has passed, you might ask what is still holding back development of quantum computers and why aren't they everywhere yet? Well, it's still possible that quantum computers will never take place and even when they eventually do, they won't make classical computers obsolete. It is because they do different things better. Much like classical physics does some things better and quantum physics other things. You wouldn't want to use quantum mechanics to build a entire car or boat. Trust me, you really wouldn't.

Further reading: Minds, Machines and Multiverse: The Quest for the Quantum Computer by Julian Brown.