Quantum Computing

Quantum Computing Image. Source: Image from New Scientist, 2018.[(https://www.newscientist.com)]
Quantum Computing Image. Source: Image from New Scientist, 2018.[(https://www.newscientist.com)]

Quantum computers are next generation computers that are extremely powerful machines with a new approach for processing information. They are built on the principles of Quantum Mechanics. Instead of bits, which conventional computers use, a quantum computer uses quantum bits—known as qubits.

Conventional computers works on a huge number of transistors to achieve the highest computing speed possible, while quantum computers use atoms and subatomic particles as their physical system. Qubits have a specific and very useful property called superposition. The superposition state allows qubits to take several values at the same time. This allows quantum computer to process much more information, much faster. A quantum computer could solve calculations in a second that would take a conventional supercomputer thousands or millions of years.

One of the first practical applications of quantum computers will be cryptography.


  • Can you explain the difference between Quantum Computers and Classical Computers?

    Classical computer is a large-scale integrated circuit based multi-purpose computer. Information is stored in bits based on voltage or charge. Information processing is carried out by logic gates such as NOT, AND, and OR gates. Circuit behaviour is governed by classical physics. Operations are defined by Boolean Algebra. No restrictions exist on copying or measuring signals. Circuits are easily implemented in fast, scalable and macroscopic technologies such as CMOS.

    Quantum computer is a high speed parallel computer based on quantum mechanics. Information is stored in Quantum bit based on direction of an electron spin. Information processing is carried out by Quantum logic gates. Circuit behaviour is governed explicitly by quantum mechanics. Quantum computers use Qubits i.e. 0, 1, and both of them simultaneously to run machines faster. Operations are defined by linear algebra over Hilbert Space and can be represented by unitary matrices with complex elements. Severe restrictions exist on copying and measuring signals. Circuits must use microscopic technologies that are slow, fragile and not yet scalable e.g. NMR (Nuclear magnetic resonance).

  • Which operating systems will control Quantum computer?

    At present researchers at Cambridge have designed one of the very fastest OS for quantum computing which is named as t|ket>.

  • Can you explain qubits?

    Qubit is a unit of quantum information. Qubits have special properties that help to solve complex problems much faster than classical bits. One of these properties is superposition, which states that instead of holding one binary value like a classical bit, a qubit can hold a combination of '0' and '1' simultaneously. When multiple qubits interact coherently, they can explore multiple options and process information in a fraction of the time it would take even the fastest non-quantum systems.

  • What's a Quantum Algorithim?

    Although quantum computers can run conventional algorithms, the results wouldn't be efficient. Specialized quantum algorithms can programme the superposition states of qubits to achieve higher processing power. Widely used algorithims for Quantum computing are Quantum-Circuit-Based Algorithms, Adiabatic Algorithms, Measurement-Based Algorithms, Topological-Quantum-Field-Theory (TQFT) Algorithms, Realizations, and Grover's Algorithm.

  • Will Quantum computers replace classical computers?

    Quantum computer is not a replacement for classical computers. It will be used for applications that need more processing power. Possible applications of quantum computing are the following:

    • Machine Learning
    • Medicine
    • Chemistry & Climate Change
    • Material Science & Engineering
    • Biomimetics, Energy Systems & Photovoltaics
    • Cryptography
  • Can you explain the different types of Quantum computers?

    There are two different quantum computers. One using ion qubits, the other superconducting qubits. Both five-qubit computers performed similarly, but each had its own advantages. The superconducting computer was faster; the ion computer was more interconnected, needing fewer steps to perform calculations.

  • What are the energy needs of a quantum computer?

    Quantum processors could drastically lower power consumption by a factor of 100-1000 compared to traditional silicon based servers.

  • Is Quantum computing governed by Moore’s Law?

    Moore's Law applies to transitors and silicon-based systems, where it may come to an end. However, Moore's Law may be applied on Quantum computing on Logical and Physical Qubit capacity.

  • Who's working on Quantum computing?

    As of early 2018, three major players in the U.S. plan to release quantum computing products within 18-24 months: Google, IBM, Rigetti Computing (a startup out of Silicon Valley).



Polish mathematical physicist Roman Stanisław Ingarden publishes a seminal paper entitled "Quantum Information Theory" in Reports on Mathematica.


Yuri Manin proposes the idea of quantum computing.


Lov Grover, at Bell Labs, invents the quantum database search algorithm. The quadratic speedup is not as dramatic as the speedup for factoring, discrete logs, or physics simulations. However, the algorithm can be applied to a much wider variety of problems. Any problem that had to be solved by random, brute-force search, could now have a quadratic speedup.


First working 5-qubit NMR computer demonstrated at the Technical University of Munich.


Google, using an array of 9 superconducting qubits developed by the Martinis group and UCSB, simulates a hydrogen molecule.


Intel develops a 17-qubit chip. IBM reveals a working 50-qubit quantum computer that can maintain its quantum state for 90 microseconds.


Google announces the creation of a 72-qubit quantum chip called "Bristlecone", achieving a new record.


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  2. Microsoft. 2018. "It all starts with a qubit". Accessed 2018-04-29
  3. Peter. 2017. "Massive Disruption is coming with Quantum computing." Accessed 2018-04-29.
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  5. quantum. 2018. "Quantum Computing Report." Accessed 2018-05-01
  6. Tom. 2016. "The Tiny Startup Racing Google to Build a Quantum Computing Chip." February 8. Accessed 2018-04-29
  7. Zayan. 2017. "11 facts that helps explain the quantum computer." Power Saving. Accessed on 2018-05-01.

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Devopedia. 2020. "Quantum Computing." Version 7, January 6. Accessed 2020-11-25. https://devopedia.org/quantum-computing
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Last updated on
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