Quantum Computers are computing systems that use Quantum Theory. They are different from digital computers and much more powerful. Quantum Computers are still in the nascent stage. But once they are in use, they can break the modern cryptosystem. Let’s understand what Quantum Computers actually are and how they can break the modern cryptosystem.

What is Quantum Computing?

Until the 19th century, Newtonian theory dominated physics. But, in the early 20th century, physicists discovered that the laws of classical mechanics do not apply at the atomic scale. In 1900, the German physicist Max Planck introduced Quantum Theory, according to which energy exists in individual units called ‘quanta.’

Further developments in Quantum Theory were made gradually, as per which the following holds true:

• Energy, like matter, consists of discrete units rather than solely as a continuous wave.
• An elementary particle, like an electron or a photon, can behave like either a particle or wave.
• The movements of elementary particles are random and unpredictable.
• The more precisely the position of some elementary particle is determined, the less precisely its momentum can be known. In other words, the more precisely one value is measured, the more flawed will be the measurement of the other value.

Later, the theory of quantum superposition was developed. As per this theory, any two quantum states can be added together or superposed to create another valid quantum state. In fact, as long as we do not check to see the state an elementary particle is in, it can be in all possible states simultaneously.

To illustrate the above principle, a thought experiment called Schrodinger Cat was described by Erwin Schrodinger in 1935. As per this:

Suppose a cat is pinned up in a steel chamber along with a device that contains a tiny bit of radioactive substance. The atom from the substance may decay in an hour. When the atom decays, it would shatter a small flask of hydrocyanic acid, which could kill the cat.

This would mean the cat will be alive as long as no atom decays. But if it does, the cat will be killed by the poisonous hydrocyanic acid. We would not know whether the cat was alive or dead as long as we broke the steel chamber.

So, to draw an analogy, the cat will be in a state of superposition of being alive and dead as long as it is in the steel chamber. And when we break the steel chamber, the cat will be either alive or dead.

According to the theory of entanglement, two elementary particles can be entangled with each other so that their states correlate. For example, two electrons can be entangled.