Quantum Computing: how it works and what it can do


Author – Irene Anna Kurien


The ubiquitous classical computers we use today are amazing and has a great effect in our daily life. We use the internet in almost everything we do, it has turned our existence upside down. But some problems are simply unsolvable by these machines, such as, problems that have their time complexity rising exponentially. For example, understanding chemistry and material science or a case of optimization, the limits of classical computers are bounded that after a certain point we run out of computational power. So why do physicists say that quantum computers can come up with solutions for problems that are virtually impossible for a classical computer to solve? 

Are quantum computers a powerful version of classical computers?

No, they are not! 

Then how do they differ?

While a classical computer encodes information in classical bits(0 or 1), quantum computers use quantum bits or qubits than can exist either as zero, one, or both at the same time. They exploit the two main principles of quantum physics – superposition and entanglement. Superposition means that each qubit can represent either a zero or one or both at the same time and entanglement happens when two qubits in a superposition are correlated with one another, the state of one depends on the state of the other. Quantum computers “manipulate the properties of quantum entangled qubits to simultaneously try a vast number of solutions, rather than trying each in turn” [Rob Gear]. They change how we run algorithms today. 

If we consider two bits they can exist in as 00, 01, 10 or 11 i.e., just two bits of information, but to describe the one-ness and zero-ness of two entangled qubits in superposition state we need four coefficients or they exist in four states. Thus the amount of classical information contained in N entangled qubits is equivalent to 2^N classical bits. And the most interesting part of this exponential increase is that if we have three hundred entangled qubits, then we have 2^300 classical bits, which is as many particles as there are in the universe! The power of quantum computers to represent N bit in 2^N system states and perform parallel operations on all those states at once allows quantum computers to solve certain complex problems of the world much more efficiently.

What quantum computers can do?

Some of the potential applications of quantum computing can be seen in the stimulation of real-world phenomena like in pharmaceutical discoveries, weather forecasts, building optimal solutions, security and encryption, and many more. Several organizations have already invested in quantum capabilities. Let’s look into some of its applications.

  1. Drug Development and Material Science: Quantum technologies can transform the health and medical sector by helping us untangle complex molecular structures and chemical interactions. The calculation of the quantum properties of all the atoms in a molecule is a computationally difficult task in today’s world. Quantum computers can explore thousands of combinations in parallel and reduce the time and financial costs associated with discovering new drugs.
  2. Supply Chain and Logistics: Quantum computers are good at finding optimal solutions that can be of great aid to the supply chain. Let’s take the example of finding the shortest route between two places or finding the way out of a maze. What classical computers do is that they would check each possible route one at a time to find the efficient one which requires a lot of computing. While a quantum computer uses its entangled quantum state to find the correct route quicker with far fewer calculations. With it, you could try every possible route all at the same time, and choose the optimal one. This optimal route can be used by a delivery boy or a salesman to cover a region in the least time.
  3. Financial Services: The financial sector involves a great deal of computation to run markers and quantum computers can help them make better investments by finding new ways to handle financial data and isolate global risk factors.

Having said all these the quantum computers have some downsides as well, the advantages and disadvantages of supercomputers are inseparable. The qubits are so delicate that any interaction with the environment can cause errors in computation.

A quantum computer is never a replacement for classical computers. They can deliver solutions where sufficient data does not exist or if data is too enormous for classical computers to compute. Its ability to solve complex problems will transform the way we live today. 


Irene Anna Kurien

Rajiv Gandhi Institute Of Technology

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