The promise of quantum computers
Introduction
We hear this word everyday ‘Quantum Computers’, so what actually are Quantum Computers and how are they different from the classical computers we currently have in our possession? The question seems simple but it doesn’t have that straightforward answer. Let’s try to understand it from the problems that we currently have with the Classical Computers :
The processors inside the computer are getting smaller and smaller every year (e.g the Intel’s latest i9 series are 14nm chips), and the smaller the chips the more efficient they will be, but even with the latest processors and chipsets we are unable to perform many computations and simulations, because the classical computers primarily work on the principal of bits where at a given time a bit can be either 0 or 1. The basic building block of Classical Computers are transistors .These transistors are used as a switch that is either on or off at a given instant of time.There is of course a limit of how fast these transistors can work and because of that some computational tasks might take exponential time limit. There are also many Medical Challenges and Physics problems that can’t be solved with the present Super Computers we have.
Quantum Computers
Quantum Computers have data in the form of quantum bits or Qubits . Quantum computer performs calculations based on quantum mechanical properties like Superposition, Entanglement and Interference. Lets’ understand these three terms in little more detail:
· Superposition :- “Superposition”, is where subatomic particles appear to exist in multiple different states simultaneously ,i.e the qubit can be 1 or 0 at the same with. Example: A single photon of light, when beamed through a prism that sends half the light to the right and half the light to the left, appears to travel both the right path and the left path at the same time.
· Entanglement :- ‘Entanglement’ means some sort of correlations between the particles where the quantum state of one particle (such as the direction of its spin) could be determined from the state of another particle, regardless of how far apart the two particles were when the state was measured. Example :- if the two particles are correlated and we change the spin of one particle, then the spin of the other particle will automatically be changed. Seems unrealistic ?? Welcome to the Quantum World
· Interference :- ‘Interference’ can be of two types :
o Constructive Interference :- Constructive interference occurs when the maxima of two waves add together (the two waves are in phase), so that the amplitude of the resulting wave is equal to the sum of the individual amplitudes.
o Destructive Interference :- Destructive interference occurs when the maxima of two waves are 180 degrees out of phase . In other words the maxima of one wave falls on the minima of other and leads to complete or partial cancellation.
What’s a qubit?
For starters, when we assign digital values to a switch in a classical computer, we call that a “binary digit”, or “bit” for short, but when we assign values to some aspect of a subatomic particle, we call it a “quantum bit”, or “qubit”.
More importantly, a classical bit can only be either a 1 or a 0 at any moment in time, but a qubit, when it’s placed into a state of superposition, can be thought of as being both a 1 and a 0, at the same time.
Let’s understand its working by a simple example :-
Imagine we are trying to guess a cryptographic key with a Classical Computer.
A naive approach (known as a “brute-force attack”) would be to guess at it over and over till we guess right. The first guess, expressed as an eight-bits of data, might be : 00000001. Second guess might be : 00000010. Then third : 00000011. Shuffle through all the combinations of bits and eventually we might guess the right answer.
Now imagine using qubits instead of bits. Every qubit is both a 0 and a 1 at the same time, so our first guess is the only guess we need. It tries every combination of “1” and “0” at the same time.
This is the Power of Quantum Computer.
Summary
· Quantum Computer are capable of solving very complex problems in matter of seconds.
· In Classical Computers bits are the smallest piece of information that can be transmitted, whereas in Quantum Computers Qubits are the smallest piece of information.
· Quantum computer performs calculations based on quantum mechanical properties like Superposition, Entanglement and Interference
· Quantum computers don’t give us exact value or fixed value of some problem, rather it gives us in the form of probability associated with each possible value of that problem.
References
· https://www.physicsoftheuniverse.com/topics_quantum_superposition.html
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