By Liya Johnson
Nowadays everybody seems to be talking about this genius, complicated and in a way kind of mysterious entity called quantum computer. Articles titled The Next Tech Revolution, talking about superposition, quantum entanglement, qubits and many other things we don't fully grasp are all over the internet. So what exactly is all this hype about. Continue reading to find out more :))
So before we start breaking down the core concepts behind quantum computing, let's clear some common misconceptions, NO! quantum computers are NOT an advanced, better, faster version of classical computers. They are in no way synonymous to each other and are better at different things. Matter of fact quantum computers are not faster than classical computers at everything. For example the operation of addition is much simpler and faster if done by a classical computer.Hence QC’s will complement rather than replace existing technologies. Quantum computers come into play when we have to deal with multiple variables interacting in complicated ways. Modelling the behaviour of atoms in a molecule is one such complex problem.
Now unlike classical computers or supercomputers (which are simply large scale classical computers) QC’s don't work on 0’s and 1’s (bits). Instead they use something known as a qubit (quantum bit) to run multi dimensional quantum algorithms.
A qubit itself isn't very useful. But it can perform an important trick: placing the quantum information it holds into a state of superposition, which represents a combination of all possible configurations of the qubit. Woah lets take a pause there. You must be wondering what this ‘superposition’ is. It is the ability of a quantum system to be in multiple states at the same time until it's measured. Which means unlike classical bits which have a value of either 0 or 1, qubits will have a combination of different probabilities of the states of 0 and 1 until we measure it. Remember Scrodinger’s cat ? There the cat is said to be in a superimposed state of being both dead and alive until we observe it. To simplify it further, it's like having a magical coin spinning in the air which is both heads and tails and you will know the result only once you catch it.
Groups of qubits in superposition can create complex, multidimensional computational spaces. If we consider 2 classical bits, its 4 combinations are 00, 10, 01, 11 all having an equal probability of 25% (1/4). But if we consider 2 qubits the possible combinations are α|00⟩ + β|01⟩ + γ|10⟩ + δ|11⟩, the probability of them existing in each of these states differ. It depends on the probability amplitudes (,,,) of each state. As more qubits are added the number and complexity of these probable states increase exponentially offering the potential for quantum computers to perform computations in parallel across this vast space of states.
Complex problems can be represented in new ways in these spaces..
Computation on a quantum computer works by preparing a superposition of all possible computational states. A quantum circuit, prepared by the user, uses interference selectively on the components of the superposition according to an algorithm.
Interference is when quantum mechanical waves(which are mathematical probability waves ) interact (either constructively or destructively) leading to change in probability of measuring certain outcomes. Many possible outcomes are canceled out through interference, while others are amplified. The amplified outcomes are the solutions to the computation.
And there it is, you now know a little bit more about how quantum computers function !!!!
Sources
https://www.ibm.com/topics/quantum-computing
https://scienceexchange.caltech.edu/topics/quantum-science-explained/quantum-superposition