CAJ: Simulation Theory - 7.) The Quantum Computer as magic key

In my previous posts, I wrote about how we might find out that we are living in a computer simulation. Now, I want to focus on the computer which is needed in order to perform such large-scale simulations of more complex physical systems in which also humans might be generated. 

At the current state of knowledge and of computer technology, the secret of success is a Quantum Computer. 

The first mystery which needs to be solved in relation with a quantum computer is the question: “What is a quantum computer? And in which way is it different to a normal digital computer?”

Traditional computers have been in use for the majority of the 20^th century. The quantum computer is a relatively new phenomenon. It has been first theorized by Paul Benioff in 1981 when he managed to apply quantum theory to computers. He theorized creating a quantum Turing machine.  

Turing machine

The “Turing Machine” plays an important role as most digital computers are based on the Turing Theory. In the 1930’s, Alan Turing developed the Turing machine which is a theoretical computing device which serves as an idealized model for mathematical calculation. It consists of a tape unlimited in length which represents the unlimited memory capacity. The tape is divided into little squares and on every single square can be printed a symbol. So it can either be a 1 or 0 or a left blank. Further, the tape can be moved back and forth which is the elementary operation of the machine. At any moment there is one symbol in the machine and this symbol is called the “scanned symbol”. The machine is capable of altering the scanned symbol and the behavior of the machine is also partly determined by that symbol. However, the symbols elsewhere on the tape do not affect the behavior of the machine. A Turing machine can be adapted to simulate the logic of any computer algorithm. 

The major difference of a Turing machine and a quantum Turing machine is that the tape exists in a quantum state which means that the symbols on the tape can be either 0 or 1 or a superposition of 0 and 1. So the symbols are both 0 and 1 at the same time. This allows the quantum Turing machine to perform many calculations at the same time whereas the normal Turing machine can only perform one. 

As already mentioned above, todays digital computers work like a Turing machine by manipulating bits that exist in one of the two states: 0 or 1. In contrast, a quantum computer works a little differently. These types of computers are not limited to two states. They encode information as quantum bits or qubits, which can exist in superposition. Qubits represent atoms, ions, photons or electrons and their respective control devices that are working together to act as computer memory and a processor. Because a quantum computer can contain these multiple states simultaneously, it has the potential to be millions of times more powerful than today's most powerful supercomputers. This superposition of qubits, according to physicist David Deutsch, provides a quantum computer with its inherent parallelism which allows the computer to work on a million computations at once, while our normal computer works only on one.

A problem that arises with the idea of a quantum computer is that by looking at the subatomic particles, physicists might bump them and thereby change their value. Which basically means that if physicists are trying to look at a qubit in superposition to determine its value the qubit will take the value of either 0 or 1. So they can only get the value at the moment of measuring which is different to the value of the qubit before the measurement because the qubit was in a state of superposition. As a result, the quantum computer turns into a normal digital computer. To solve this problem scientists have to find other ways of making measurements to preserve the system’s integrity. Therefore, quantum computers also utilize another aspect of quantum mechanics known as entanglement which might be the solution to the problem. In quantum physics, if you apply an outside force to two atoms, it can cause them to become entangled and the second atom can take on the properties of the first atom. So if left alone, an atom will spin in all directions. The instant it is disturbed it chooses one spin, or one value; and at the same time, the second entangled atom will choose an opposite spin, or value. This allows scientists to know the value of the qubits without actually looking at them.

However, it has to be mentioned in a very interesting interview with Rainer Blatt, physicist at the

University of Innsbruck - Rainer Blatt

University of Innsbruck, that there do exist models of quantum computers even though the technology is not extremely developed. At the University of Innsbruck they are currently working with two quantum computers. He explained briefly what they look like. Basically, it looks like a normal laptop or computer but is just slightly bigger and unhandy. Further, he is still placed in the laboratory. So he cannot be sold at the current state of technology. It would be possible to build it up on a desk and a laser and a normal computer would be needed to work with it. 

In general, he mentions that this type of computer even though it can be seen as a universal computer will not be needed for private usage. We will need it to solve more advanced problems. So it is a device that can calculate some things better than normal computers but will not be needed for other things like Office-applications. 

looking at the heart of a quantum computer in Innsbruck

One particular interesting aspect of the future use of quantum computers is cryptography, especially the RSA-algorithm. With this algorithm we are currently decoding data and communication. The secret behind this method is that you have a very big number from which you know that it can be divided into two prime numbers. The act of dividing is very difficult for humans as well as for normal computers. Therefore, it is called a hard problem. Since twenty years, there exists an algorithm with which you could decode the encryption program on a quantum computer. As a result, there are many institutions particularly interested in the fast development of quantum computers such as CIA, NSA but also companies as Google or Amazon. 

Rainer Blatt also explained that the primary goal nowadays is to develop quantum computers because you can solve problems which you cannot calculate efficiently at the moment. Especially simulations are seen as major beneficiaries of this type of computer. A quantum computer could easier simulate quantum mechanical characteristics of materials. Simulations of normal computers are not useless but they can only determine an approximate value. 

sources:

http://computer.howstuffworks.com/quantum-computer.htm

http://blogs.faz.net/digitaltwin/2014/03/13/wie-funktioniert-ein-quantencomputer-350/

http://en.wikipedia.org/wiki/Quantum_computer

http://mathworld.wolfram.com/TuringMachine.html

http://en.wikipedia.org/wiki/Turing_machine

http://www.zeit.de/wissen/2014-04/surren-blinken-leben-quantencomputer/seite-2