Tuesday, January 19, 2016

Quantum Computers - Taking Human civilization to a whole new lavel



Need to move on from classical computers

 We know that our computers perform the daily life calculations and solve our engineering problems. We do our office work on these computers and We can also watch videos, listen to music, surf the internet and play games. All of these computers including personal computers, workstations and super computers are conventional computers. Because all of these use binary to do everything they do. They use the combinations of 1s and 0s. Everything including sounds, videos and images are represented using binary in these computers. Computers make their decisions in 1s and 0s using logic circuits using some basic logic gates which work on high and low voltage and computers recognize the high voltage as a 1 and low voltage as a 0. We call these 1s and 0s as bits. A bit can either be 0 or 1. 
The problem with our current computers is that we're close to hitting the limit for how advanced they can get, Plus, classical computer cannot solve some complex problems; those involving very large number of variables or some complex optimization problems.

The strange & fascinating world of Quantum mechanics


 Our perception of reality has completely changed over the past seventy-five years, because of the new revolutionary set of laws; the laws of quantum mechanics. These laws govern every atom in every piece of matter in stars and galaxies, rocks and oceans, and in you & me. And for decades now, scientists have been trying to use these strange laws in order to devise a whole new generation of computers; Quantum computers.
Quantum computer uses sequence of quantum bits or simply; Qubits, not the conventional or classical bits. The difference between a conventional bit and quantum bit is that a bit can either be 0 or 1 at a time where as a Qubit can be both 1 and zero at the same time which makes the quantum computers very powerful.  This is hard to understand because these concepts are from physics. Precisely, quantum mechanics. And the roots of quantum computing lie deep down in the strange and mysterious laws of quantum mechanics. And the bizarre predictions made by them; Phenomenon’s like Quantum superposition, Quantum entanglement etc. I strongly recommend you to read my previous post in order to understand these things, which is in turn, important to have a better understanding of the working of quantum computers.


Working of Quantum computers

 Quantum computers are fundamentally different from the classical computers. Due to the fact that a classical bit can either be 0 or be 1 at a time. Whereas, a Qubit can be 0,1 or both at the same time. Precisely, superposition state of 0 and 1, in case of quantum computers, a bit (Qubit) is not in the form of voltage, rather a Qubit can be anything which behaves quantum mechanically; atom, electron, photon. Take electron for example; according to the laws of quantum mechanics; the spin motion of electron can either be clockwise, anticlockwise or superposition of both. It means that an electron can spin in a lot more ways than clockwise and anticlockwise. Unless you measure the spin state of the electron, it is in the superposition. The act of measurement forces it to acquire one of the states, we can say clockwise to 1 and anticlockwise to 0 or vice versa.  This spin motion of electron serves as a qubit. But there's a catch; when we measure a Qubit, it transforms and collapses itself into a simple classical bit. That’s why quantum computers are not very good alternative for small daily life calculations involving some amount of steps. However, quantum computers are indeed exponentially faster in case of calculations involving a lot of variables. Checking a lot of possible combinations to find one right answer, hit and trial kind of operations. Like those involved in cryptosystems. Or calculations involving trillions of variables, for example; to determine what happened at the instant of big bang. Because of the reason that we don’t need any intermediate results in these long calculations, instead we only need to arrive at the final answer, we don’t disturb the qubits by measuring them halfway through the calculations. We don’t need to, which allows them to work efficiently. To understand how qubits work, consider 2 bits and 2 qubits. The state of a 2-bit classical computer will be one of these four possible states, whereas, a two Qubit quantum computer will be in superposition state of all these our states, like being in all the states at a time.




Furthermore, for two bits there are four possible states; 00, 01,10,11. Now in case of classical bits, in order to determine the state of computer we only need to have two pieces of information. In which state both bits are, so they will be two pieces of information. However, in the case of quantum bits, quantum mechanics allows us to create the superposition state of the four states which will be some coefficient say A times 00, B times 01, C times 10 and D times 11. And all of these coefficients are complex. So basically now we need 4 pieces of information. That’s how 2 qubits have 4 classical bits. When we’ll have 3 qubits, we’ll need to have 8 pieces or 8 bits of classical bits in order to determine the state of computer. This makes the quantum computers exponentially powerful than classical computers. And the power of exponentials means that when we’ll reach 300 qubits which are fully entangled with each other we’ll have more classical bits then there are total atoms in the observable universe.

 It is again, worth mentioning that Qubits can be anything. Spin motion of electron in the presence of magnetic field, motion of nucleus, photons. Everything which behaves quantum mechanically can be used as a Qubit.  For these new kind of Qubits, new gates are to be developed depending on what is being used as a Qubit. For example, if photon is being used as Qubit; such gate should be developed which could control the photon. Possibly optical materials be used in that gate. If spin motion of electron is to be used as Qubit, some magnetic kind of materials will be used to develop gates, there is no hard and fast rule for now, as this field is in its infancy, different experiments are being made and different kinds of Qubits and different approaches are being used.

In addition to this, it is necessary that all the Qubits involved in a quantum computer must be entangled with each other; in order to achieve maximum potential of the computer.
Plus, in order to make use of all the fascinating quantum properties of quantum particles, they are needed to be calmed down; cooled down to the very low temperatures; to fractions of degree kelvins above absolute zero. Furthermore, in order to reduce quantum noise they are needed to be kept in highly maintained conditions where even the sound of a car passing through the road outside your home cannot reach, because that will disturb the behavior of quantum particles.
That's why there's a low chance that you'll ever use a quantum computer in your home.

Approaches to Quantum computing

There are two general approaches to quantum computing; quantum gate model computing and quantum annealing approach.
Gate model quantum computing involves the controlling of quantum state of the qubit/particle involved, and as quantum particles are highly delicate and very difficult to control, so this is model of quantum computing is very slow in its progress. However, more control means that this gate model quantum computer can solve higher class of problems. Specially Shore’s algorithms for factorizing numbers and Grover’s algorithms for searching in the large 
whereas, Quantum annealing does not require the control over quantum state of particles, rather it just determines the best and most suitable answer by using energy levels. The lowest energy corresponds to the best answer. 
It is Used by the D-wave systems; first quantum computing company. So far, quantum computer of 1097 Qubits has been developed using this approach.

Commercially available Quantum computers

‘D-wave systems’ is the first and the only recognized quantum computing company. Till now, they’ve released 2 quantum computers. D wave one and D wave 2x.
D-wave one was released in 2011, it was the first ever commercially available quantum computer. It is a 128 qubit processor based on quantum annealing. It was followed by collaboration b/w google Inc., NASA and USRA. It solved optimization problems and its price is US$ 10,000,00.
Later is found proven that this quantum computer was no better than the classical computers in terms of speed.



                                                                                     
D-WAVE 2x was a giant leap forward in the field of quantum computing. It is based on 1097 qubit quantum annealing processor. It is not a general purpose computer, but rather it solved only a specific class of problems called optimization problems. It was placed in Google headquarters and google claims that it solved a problem in seconds which a classical computer would have taken 10,000 years to solve.
In D-wave 2x, a particle is said to be entangled with 6 other particles at the same time. D wave 2x is said to be 100 million times faster than classical computers in terms of solving these optimization problems.

                                                                                           
It must be mentioned here that these are not Gate model quantum computers on which Grover’s algorithm or Shore’s algorithm. And these are rather quantum chips which can solve certain limited problems. 



Conclusion

Although quantum computers don’t seem to be a perfect replacement for classical computers. However, they can solve the problems which classical computers can never solve and are immensely powerful; to the scale of being regarded as a threat to human civilization.  Looking at the current situation, Quantum computers seem to be the future of mankind. If used positively, they have huge potential to make human civilization enter into a new era, an era where there will be no more scientific problems left. Time travel, Human teleportation and all the science fictions we see in the movies today would take the colors of reality. Although It seems to be a far fetching Idea today but for those who allow their imaginations to roll, Even the sky is not the limit.







No comments:

Post a Comment