A quantum computer uses quantum principles like superposition, entanglement & interference for computation. The quantum particles behave differently than our classical perception known as Quantum Weirdness.
Superposition is the existence of two states simultaneously. For example, an electron exists in both particle and wave. But when we observe its wave nature collapses and it becomes more localised as a particle. Quantum entanglement says that when two particles are entangled, we can predict the outcome of one by measuring the other. No Matter what is the distance between them. Which Einstein said spooky action at a distance. The principle of interference is used to amplify the desired results in the quantum computer.
How it works:
Classical computers use bits (binary digits) like 0s and 1s to carry out operations. A bit can exist in one of the two states i.e. either 0 or 1. But a quantum computer uses qubits (quantum bits) instead of bits like classical computers. A qubit is the superposition of both 1 and 0. You can visualize it as a spinning coin. In which there is some probability of head and some probability of tail. One qubit can be represented as,
ᴪ= C1|0> + C2|1>; C12+ C22=1
C12 & C22 are the probabilities of |0> & |1> respectively
Similarly, superposition of 2 qubits can be represented as;
ᴪ= C1|00> + C2|01> + C3|10> + C4|11>
Similarly if you have n qubits you will require 2n numbers (C1, C2, C3,….Cn) to specify the superposition state.
mathematical stuff:
A bit can be defined as;
One qubit , ᴪ= C1|0>+C2|1>; can be represented by;
for e.g. ᴪ= C1|0> + C2|1>;
The quantum state can be represented on the circumference of a unit circle. The state vector joins the quantum state to the origin.
If we have two qubits, we have four basic states;
The superposition state can be represented as ;
ᴪ= C1|00> + C2|01> + C3|10> + C4|11>
It requires a four-dimensional vector to define the quantum state. The superposition state is a point on the surface of a sphere in four-dimensional space. But it is hard to visualise.
If we have n qubits it requires 2n dimensional vector to define the quantum state.
Let’s take a basic state an apply the quantum gates. Quantum gates are the gates in quantum computer which change the states in quantum operations. The quantum computer works on superposition principle. But at the end of the calculation its superposition states collapse to give a definite result.
In vector form:
How to make a qubit in practice:
A qubit can be made by ion traps, optical traps, quantum dots, superconducting circuits, semiconductor impurities. We will discuss the easiest one i.e. a qubit made by semiconductor impurities. The phosphorous atom is placed inside a silicon crystal. The outermost electron of the phosphorous acts as a qubit. The whole arrangement is placed between an external magnetic field. Now the electron revolves under the effects of two fields (field of the nucleus and the external field).
The energy difference between the spin 1(higher energy state) and the spin 0 (lower energy state) is proportional to the applied external magnetic field. The dope material is so cooled (nearly absolute zero) that no thermal energy can disturb the spin of the electron. Specific energy of radiation is given to toggle between the spin |0> an |1>.
Different parts of quantum computer:
Some important parts of the quantum computer are;
1.Superconducting Coaxial lines are used to connect different amplifying stages. To minimize energy loss, they are made of superconducting materials.
2.Cryogenic Isolators filters the noise from the qubits.
3.Quantum Amplifiers amplify the qubit signals
4.Cryoperm Shield contains the quantum chip inside it. It protects the shield from external electromagnetic radiation.
5.The Mixing Chamber cools the quantum chip and the necessary parts to 15mK. It is the lowest part of the computer.
The temperature decreases from the top to the bottom. Finally, the whole apparatus is placed inside a vacuum refrigerator. The refrigerator uses Helium as the coolant.
Quantum supremacy:
Quantum supremacy is to show the quantum computer superior to classical computers and supercomputers. In 2019 google claimed that it has achieved quantum supremacy. Google claimed that their quantum computer performed the task in a few minutes which a classical computer needs years to solve. But IBM denied Google’s claim. Honeywell also claimed that they have built the fastest quantum computer. Now IBM is providing access to their Quantum Computer through cloud across the world.
Application of quantum computer:
Quantum computers can be used to design the molecules of drugs. Because when it comes to design a large molecule involving no. of atoms we have to consider every possible repulsion and attraction between electrons, bonds. When no. of the atom increases the problems increase exponentially.
So, it is quite difficult for classical computers. But the quantum computer can solve it faster than the classical computer. Quantum computers can find the prime factor of large no. faster than classical computers. Because, when the number increases the computer has to test the divisibility of the number with every prime number. As qubits exists in superposition state the quantum computer can solve it lesser steps.
But it may not replace your classical computer. It is a totally different technology and only powerful than a classical computer in some areas. In the future, we may not able to buy the Quantum computer for personal use because the computer works at a very low temperature. It is also very sensitive to any external noise. So, quantum computer explained.
