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Quantum Computing – How Does it Work

November 14 2019
Author: Blogauthor
Quantum Computing – How Does it Works

“Quantum Computation is….a distinctively new way of harnessing nature….It will be the first technology that allows useful tasks to be performed in collaboration between parallel universes.” - David Deutsch

Sounds unbelievable, Doesn’t it? Well! The fact is that quantum computing opens doors to innumerable possibilities which were earlier thought to be impossible!

We have all experienced the benefits that classic computing offers. However, there is a limit to how much classic computing can offer us because classic computing does not have the computational power to tackle problems of a certain size and complexity.

Quantum Computing opens new doors

A paper published by Google computer scientists appeared on a NASA website that spoke of an innovative new machine called Quantum Computer. This computer had performed a highly technical and specialized computation in three minutes which would have taken a regular computer 10,000 years to work out!

Before we delve into what quantum computing is, let us understand what Quantum mechanics is and how quantum mechanical phenomena help in advanced computations.

Initial research in quantum mechanics started way back in the 17th century when scientists proposed the wave theory of light according to which light exists both as wave and in particle form.

Quantum Mechanics is a field that deals with matter and its interactions with energy on the scale of atoms and subatomic particles.

Further research in quantum mechanics revealed that an atom comprises a small positively charged nucleus with negatively charged electrons that travel in circular orbits around it. Each orbit is at a different energy level. The transition of an electron from one orbit to another is done in discrete quanta.

This transition was termed a “quantum leap” and it was special because the electron did not move progressively. On the other hand, it simply disappeared from one orbit to appear in another with the release of energy. This quantum of energy cannot be further subdivided. Since the first insights to these energy levels were provided by a physicist named Planck, it is called Planck’s Constant.

Further research was conducted to find out why electrons follow quantized orbits and do not have intermediate states. Louise de Broglie in 1923 proposed an explanation for this. He said that matter, just like light, exhibits both wave and particle nature. Therefore, electrons obtain certain wavelengths because of which they fit in an orbit. However, due to the wave nature of the electron, it exists at all places not just one spot. However, in the case of matter with higher mass, the momentum is high, and wavelength is very small. So, the theory does not hold at macroscopic levels.

Werner Heisenberg and Neil Bohr proposed the Copenhagen interpretation of quantum mechanics which states that physical systems generally do not have definite properties before being measured and quantum mechanics can only predict the probabilities that measurements will produce certain results.

The laws of quantum mechanics can lead to some counterintuitive results such as that an object can have a negative mass. Scientists around the world are exploring real-world deployments of technologies based on quantum mechanics.

What is Quantum Computing?

Quantum computing is performing calculations based on an object’s state before it is measured instead of 1s or 0s. This implies that quantum computing has the potential for processing exponentially more data than classical computing.

Classical computing carries out logical operations using definite positions of a physical state. These physical states are usually binary states. The operations are carried out in one of the binary states which could be “on” or “off”, “1” or “0”, or “up” or “down”. These states are called bits.

On the other hand, quantum computing operations are performed using the quantum state of the object which is known as a “qubit.” A qubit can be understood as the undefined properties of an object before it has been detected. For example, the spin of an electron or polarization of a photon.

Unmeasured quantum states occur in a mixed ‘superposition’ instead of having a clear position. These superpositions can be ‘entangled’ with those of other objects leading to mathematically related outcomes.

The complex mathematics behind the entangled states can be used for creating special algorithms for quantum computers which will result in faster computing. These computations will be too complex and will take a long time for classic computing.

In other words, quantum computing leverages quantum mechanical phenomena of superposition and entanglement to create states that scale exponentially with the number of qubits.

How does Quantum Computing Work?

There are essentially three quantum mechanical properties used to manipulate the qubit for quantum computing. These are:


Superposition is a quantum phenomenon in which a quantum system can exist in multiple states or places at the same time. Superposition eliminates the constraint of computing with the binary system by offering qubits that can take the value of 0 or 1 or both simultaneously. A quantum computer is capable of holding data using a system that can exist in two states at the same time due to the superposition principle of quantum mechanics. A qubit can hold two values 0,1 simultaneously, two qubits can similarly hold 4 values-00,01,10,11 and so on.


Quantum entanglement is a phenomenon by which more than one particle generated together or closely interacted can start a relationship and the quantum state of each particle cannot be described independently.

Entangled qubits have an effect on each other instantly irrespective of the physical distance between them. This is a very powerful impact when compared to a traditional computer that needs to read and write from each element of memory separately before operating on it.

Entanglement leads to:

  • Increase in the execution of complex programming for certain types of problems.
  • Modeling of complex molecules and materials that are hard to simulate with classical computing.
  • Innovations in long distance secure communications.


Quantum states also undergo interference due to a phenomenon known as a phase. Quantum interference can be conceptualized as wave interference. Just like a wave interference when two waves are in phase their amplitudes add and when they are out of phase their amplitudes cancel.

How do Quantum Computers Compute?

Just like a classic computer, in quantum computing, you require a set of instructions with a problem-solving approach(an algorithm) and a computer to execute the algorithms. However, unlike classical computers, quantum computers can create entanglements, superpositions, and other quantum effects. This implies that the algorithms are written in a new way which was beyond the scope of classic computing.

What is Quantum Computing used for?

Quantum computing finds applications in areas such as:

Artificial Intelligence (AI)

AI works on the principle of learning from experience and enhancing accuracy with feedback until the computer program becomes intelligent.

This feedback is based on calculating the probabilities for different choices, so Artificial Intelligence is best suited for quantum computing. It has the potential to disrupt every industry from automotive to medicine.

Molecular Modeling

Google has made a foray in the field of complex chemical reactions by simulating the energy of hydrogen molecules. This implies more efficient products from solar cells to pharmaceutical drugs and fertilizer production.


Most online security depends on the complexity of factoring large numbers into primes. Quantum computers are capable of performing such factoring exponentially more efficiently than digital computers. New cryptography methods are being developed with the help of quantum computing.


Quantum computing has opened new doors as these computers are capable of performing gazillions of calculations simultaneously. These calculations have the potential to break currently unbreakable codes and solve unsolvable mathematical puzzles. Google, IBM, Microsoft, etc. have already started designing and building the starter versions of a quantum computer. And, the future sure looks exciting!