Quantum computer- What is it?

For most of our history, human technology consisted of our brains, fire, and sharp sticks. While fire and sharp sticks became power plants and nuclear weapons, the biggest upgrade has happened to our brains. Since the 1960’s, the power of our brain machines has kept growing exponentially, allowing computers to get smaller and more powerful at the same time. But this process is about to meet its physical limits. Computer parts are approaching the size of an atom! To understand why this is a problem, we need to clear up some basics.

Quantum computer is that computer which does its entire works using quantum mechanics. It uses Entanglement, Teleportation, and Superposition etc to compute or exchange information. Quantum computers can do such things that cannot be done using normal computers. But the fact is, Quantum computer cannot still be developed in the laboratory.

Quantum Computer

 A computer is made up of very simple components doing very simple things. Representing data, the means of processing it and control mechanisms. Computer chips contain modules, which contain logic gates and transistors. A transistor is a simplest form of a data processor in computers. Basically, it’s a switch that can block, or open the way for information coming through. This information is made up of bits which can be set either 0 or 1. Combinations of several bits are used to represent more complex information. Transistors are combined to create logic gates which still do very simple stuff. For example, an AND gate sends an output of 1 if all of its outputs are 1, and an output of 0 otherwise. Combination of logic gates finally forms a meaningful module, for adding two numbers. Once you can add you can also multiply, and once you can multiply you can basically do anything. Since all basic operations are literally simpler than fist grade math, you can imagine a computer as a group of little kids answering really basic math questions. A large enough bunch of them could compute anything.

However with parts getting tinier and tinier, quantum physics are making things tricky. In a nutshell a transistor is just an electric switch. Electricity is moving electrons from one place to another. So, a switch is a passage that can block electrons from moving in one direction. Today a typical scale for transistors is 14 nanometers.  Which are about 8 times less than HIV virus’ diameter, and 500 times smaller than red blood cells. As transistors are shrinking to the size of only a few atom, electrons may just transfer themselves to the other side of a blocked passage via a process called Quantum tunneling. In a quantum realm, physics works quite differently from the predictable ways we’re used to, and traditional computers just stop making sense. We are approaching a real physical barrier for our technological progress. To solve this problem, scientists are trying to use these unusual quantum properties to their advantage by building quantum computers.

Qubits 

In normal computers, bits are the smallest unit of information. Quantum computers use qubits which can also be set to one of two values.  A qubit can be any two level quantum systems, such as a spin and a magnetic field, or a single photon. 0 and 1 are this system’s possible states, like the photons horizontal or vertical polarization. In the quantum world, the qubit doesn’t have to be just one of those; it can be any proportions of both states at once. This is called superposition. But as soon as you test its value, by sending the photon through a filter, it has to decide to be either vertically or horizontally polarized. So, as long as it’s unobserved, the qubit is in a superposition, of probabilities for 0 and 1, and you can predict which it’ll be. But the instant you measure it, it collapse into one of the definite states. Superposition is a game changer. Four classical bits can be one of two to the power of four different configurations at a time. That’s 16 possible combinations, out of which you can use just one. Four qubits in a superposition, however, Can be all of those 16 combinations at once. This number grows exponentially with each extra qubit. Twenty of them can already store a million values in parallel.

Entanglement

A really weird and unintuitive property qubits can have is Entanglement. It is a close connection that makes each of the qubits reacts to a change in the other’s state instantaneously, no matter how far they are apart. This means when measuring just one entangled qubit, you can directly deduce properties of its partners without having to look.

A normal logic gate gets a simple set of inputs and produces one definite output. A quantum gate manipulates an input of superposition, rotates probabilities, and produces another superposition at its output. So, a quantum computer sets up some qubits, applies quantum gate to entangle them and manipulate probabilities, then finally measures the outcome, collapsing superposition to an actual sequence of 0’s and 1’s. What this means is that you get the entire lot of calculations that are possible with your setup, all done at the same time.