Terminologies in Quantum computing, you
must be aware of

Published by: Amit Nikhade

June 8 . 2021



Let’s go through the quantum era with the speed of light where you’ll get closer to the quantum generation


                  Massive technologists like Google, Microsoft, IBM are trying to get the most out of quantum science. John Preskill has introduced the term quantum supremacy, which states the comparison between quantum and classical computing advantages in terms of speed and performance. And, it’s also a need for us, to get into this, as fast as possible. So let’s dig in without any further intro.

We would try to understand some fundamentals of quantum computing in no time. I have tried making concepts clearer, rather than keeping them more complex. Please do hit claps only if you find it helpful. If you have any good advice for me towards improvement in the following article, please do leave a comment in the comment section.  
Here are some of the commonly used and might be you the one who is reading the post has heard about these terms often if you are into technical but not aware of what they are? 








A quantum bit or a Qubit is a rudimentary unit of information in quantum computers, i.e. the fundamental building block of quantum computing. It’s somewhat similar to the binary bit used in our classical computer, which we use in our day-to-day life. It has two states ∣0⟩ and ∣1⟩ when measured. Just consider a ball having two poles. The classical bit can be at the poles of the ball, but the Qubit can be anywhere on the ball so they can gain much information as compared to the bits. The Qubit represents any particle on a subatomic level like an electron, photon, neutron, etc.



Superposition, a circumstance where a system is in multiple states. Circumstances. The best example of superposition can be: suppose we flipped a coin, when it concludes the state while it falls on the plain, the states can be either x or y. but being in the air for time t, for that span, it simultaneously changes its state, like from x to y, y to x, and the flipping continues until it doesn’t get stable. So during flipping, it has multiple states, the condition of the coin before being stable is called a superposition.


Quantum state


A quantum state is a state in which a physical system can exist. Like in the above instance we clutched up, where we saw the coin has two states x and y, where x and y are the states of that coin. A wave function describes the states.




Entanglement occurs when the quantum state of each particle cannot be described independently of the quantum state of the other particle. A pair or group of particles interact with each other and share their fundamental properties. In which each of both particles in the pair can represent the properties of the other one. If one of them is measured it can inform about the other one. Entanglement is one of the phenomena that differentiates quantum computing from classical computing in terms of its powerful performance.




We know that all objects have wavelike properties. Suppose we split these waves into multiples, then further these waves can interfere logically to form a single wave that is the superposition of the waves we split. Interference can be used to control the quantum states, which enables us to amplify the correctness leading to perfection in the result, by just shortening the incorrect features which cause a threat to the resulting correct answer.


Quantum circuit


We can call a quantum circuit an arrangement of quantum gates, interconnect by quantum wires which involves operations on Quantum bits (Qubits). These circuits are somewhat similar to electronic circuits. However, in quantum circuits, quantum gates are used and electronic circuits are made with gates that perform electronic operations on bits.


Quantum algorithms


An algorithm refers to the sequence of instructions, which are executed one by one specifically to solve a problem. In the same way, a quantum algorithm is a step-by-step procedure to solve a problem, like a classification problem. Both the type of algorithms only differ in their medium of carrying basic information.


Quantum coherence & decoherence


In quantum computing, we describe the subatomic particles in form of waves, i.e. In mathematical terms, the quantum states of the system are represented as waves. The logical relationship between multiple waves is called coherence. The coherence should exist to perform quantum computing. As a result, the waves should pose coherent nature for solving a specific problem in Quantum computing.

Decoherence is when there is no existence of coherence. For the retention of coherence, the quantum systems are put into colder environments and isolated properly to avoid the loss of coherence due to external effects like noise. Quantum computers are extremely sensitive. If not isolated properly, they can lack information and will make improper computations.


Quantum mechanics


Physical science deals with the behaviour of the physical properties of nature on an atomic and subatomic level ( on particles like photons, electrons, molecules, etc.) is called Quantum mechanics,  It is also called wave mechanics because it considers that every particle has a wave-like behaviour.


Quantum gates



Well, Quantum logic gates are the basic building blocks of a quantum circuit that perform operations on qubits. quantum gates are reversible and are unitary operators. These gates are Reversible (reduces the wastage of heat. The reversible gates have a one-to-one mapping between the input and output vectors, this helps in constructing the input vector from the output vector). The classical operation can also be performed on the quantum gates.



Quantum complexity


The computational complexity focuses on categorising computational problems as per their resource usage. However, quantum complexity is the sub field of computational complexity that deals with complexity classes, defined using quantum computers. The complexity class is a collection of problems, where the time and energy problems are majorly and commonly analysed. In simple terms, it monitors the complexity of the problems, the difficulty level of the problem, and also compares it to the classical problem to perform the speed comparison between both.



Quantum amplitudes



The height of the wave in the figure is the amplitude of the wave.

Quantum amplitudes are nothing but probability amplitudes, they define the relationship between the quantum states of the system. Quantum amplitude is the wave function, ( the quantity associated with the moving particles with a complex nature ). It shows up the behaviour of the particle and is denoted by Ψ.



Quantum annealing

The term, Quantum annealing seems to be much complex, but it’s a quantum computing method, used to find the best solution for a problem having multiple solutions using quantum properties like tunneling, superposition, entanglement, etc.

Quantum annealing also includes adiabatic computation, it is the class that includes all the procedures to solve optimization problems using quantum computing.

Hope you’ve had a good moment and learned a lot new things or might be you were aware of those. Please hit claps if you felt the writings interesting. It will push me to create more.

 Author : Amit Nikhade

*NOTE: The post was originally published on Medium.com with MLearning.ai publication




A whole bunch of thanks to the people behind these references.


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