Quantum Supremacy: Explained

Quantum Supremacy

Context: In a paper in Nature Physics, a researcher at Google Quantum AI reportedly demonstrated a problem that is difficult for classical computers. If a quantum computer solves this problem, it can achieve quantum supremacy.

Quantum Supremacy (QS)

When a quantum computer outperforms a classical supercomputer on a well-defined computer science problem, this achievement is known as quantum supremacy.

  • Superposition states allow qubits to carry more information. 
  • Because of quantum superposition, a quantum computer can mimic several classical computers working in parallel.
  • This capacity of doing several computations in parallel gives quantum computers an advantage over classical computers, allowing them to perform a disproportionately greater number of operations.
  • Google’s quantum computer, named Sycamore, claimed ‘supremacy’ because it reportedly did the task in 200 seconds that would have apparently taken a supercomputer 10,000 years to complete.


Supercomputer is a class of extremely powerful computers. The term is commonly applied to the fastest high-performance systems available at any given time. 

  • The performance of a supercomputer is commonly measured in floating-point operations per second (FLOPS) instead of million instructions per second (MIPS).
  • Since 2017, there have existed supercomputers which can perform over 1017 FLOPS (a hundred quadrillion FLOPS, 100 petaFLOPS or 100 PFLOPS.
  • These are very large classical computers, often with thousands of classical CPU and GPU cores capable of running very large calculations and advanced artificial intelligence.

Need of Quantum Computers

  • Even supercomputers are binary code-based machines reliant on 20th-century transistor technology. They struggle to solve certain kinds of problems.  
  • When classical computers fail, it’s often due to complex problems which are problems with lots of variables interacting in complicated ways. 
  • There are some complex problems that we do not know how to solve with classical computers on any scale. 
  • The real world runs on quantum physics. Computers that make calculations using the quantum states of quantum bits should in many situations be our best tools for understanding it.

Quantum Computing

A quantum computer is a computer that takes advantage of quantum mechanical phenomena.

  • Quantum computers are machines that use the properties of quantum physics to store data and perform computations. 
  • This can be extremely advantageous for certain tasks where they could vastly outperform even our best supercomputers.  
  • Classical computers, which include smartphones and laptops, encode information in binary “bits” that can either be 0s or 1s. 
  • In a quantum computer, the basic unit of memory is a quantum bit or qubit.
  • Quantum computing is driving new discoveries in healthcare, energy, environmental systems, smart materials, and beyond.


Just like a binary bit is the basic unit of information in classical computing, a qubit is the basic unit of information in quantum computing.

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Qubits vs Bits

Qubits are represented by a superposition of multiple possible states.

  • A qubit uses the quantum mechanical phenomena of superposition to achieve a linear combination of two states. 
  • A classical binary bit can only represent a single binary value, such as 0 or 1, meaning that it can only be in one of two possible states. 
  • A qubit, however, can represent a 0, a 1, or any proportion of 0 and 1 in superposition of both states, with a certain probability of being a 0 and a certain probability of being a 1.

There are many physical implementations of qubits

  • Where classical computers use familiar silicon-based chips, qubits (sometimes called “quantum computer qubits”) can be made from trapped ions, photons, artificial or real atoms, or quasiparticles.
  • Depending on the architecture and qubit systems, some implementations need their qubits to be kept at temperatures close to absolute zero.

Qubits are fragile

  • One of the most significant hurdles in quantum computing is the fragile nature of qubits. 
  • Entanglement of the qubit system with its environment, including the measurement setup, could easily perturb the system and cause decoherence. 


Multiple qubits can exhibit quantum entanglement. 

  • Entangled qubits always correlate with each other to form a single system. 
  • Even when they’re infinitely far apart, measuring the state of one of the qubits allows us to know the state of the other, without needing to measure it directly.
  • Entanglement is required for any quantum computation, and it cannot be efficiently performed on a classical computer. 
  • Applications include factoring large numbers (Shor’s algorithm) and solving search problems (Grover’s algorithm).


  • Superposition is a phenomenon in quantum computing that allows quantum objects to simultaneously exist in more than one state or location. 
  • This means that an object can be in two states at one time while remaining a single object. 
  • Quantum computers use the entanglement of qubits and superposition probabilities to perform operations. 
  • Superposition enables the qubits of the quantum computer to perform multiple operations simultaneously, making them faster than conventional computers.

Superposition gives quantum computers superior computing power

  • Superposition allows quantum algorithms to process information in a fraction of the time it would take even the fastest classical systems to solve certain problems.
  • The amount of information a qubit system can represent grows exponentially for example Information that 500 qubits can easily represent would not be possible with even more than 2^500 classical bits.
  • It would take a classical computer millions of years to find the prime factors of a 2,048-bit number, Qubits could perform the calculation in just minutes.

Initiative taken by Indian Government towards Quantum Computing

Quantum Computer Simulator (QSim)

The launch of Quantum Computer Simulator (QSim) Toolkit by the Ministry of Electronics and Information Technology (MeitY) with an objective to 

  • Carry out research in Quantum Computing in a cost-effective manner.
  • Address the common challenge of advancing the Quantum Computing research frontiers in India.
  • Allowing researchers and students to write and debug Quantum Code that is essential for developing Quantum Algorithms.
  • Allowing researchers to explore Quantum Algorithms under idealised conditions and help prepare experiments to run on actual Quantum Hardware.
  • Feature Highlights of QSim include
    • Intuitive UI: QSim offers a robust QC Simulator integrated with a graphical user interface (GUI) based Workbench allowing students/researchers to create Quantum programs, visualise the instant circuit generation and simulated outputs.
    • Simulate noisy Quantum logic circuits: Helps simulate Quantum circuits with and without noise and test how well various algorithms work with imperfect quantum components. This is essential to simulate real-life conditions.
    • Pre-loaded Quantum algorithms and examples: QSim comes loaded with Quantum programs and algorithms providing a head start to the users. E.g., QFT, Deutsch Jozsa, Grovers, and so on.
    • Integrated with HPC: The quantum simulations are performed on powerful HPC resources allowing multiple users to submit jobs simultaneously with different qubit configurations.

National Mission for Quantum Technology and Applications (NM-QTA) 

  • To solve challenges of national importance, the mission plans to focus on fundamental science, translation, technology development, human and infrastructural resource generation, innovation, and start-ups.

Quantum communication lab (QCL) by Centre for Development of Telematics (C-DOT)

  • QCL by C-DOT indigenously developed Quantum Key Distribution (QKD) solution which can support a distance of more than 100 kilometers on standard optical fiber.

Indian Army’s establishment of quantum laboratory

  • Army, with support from the National Security Council Secretariat (NSCS) has established the Quantum Lab to spearhead research and training in this key developing field. 
  • Research undertaken by the Indian Army in the field of quantum technology will help leapfrog into next-generation communication and transform the current system of cryptography in the Indian Armed Forces to Post Quantum Cryptography (PQC). 
  • Key thrust areas are quantum key distribution, quantum communication, post-quantum cryptography and quantum computing.

Quantum Information Science and Technology (QuST)

  • Department of Science and Technology (DST), Government of India has initiated a new directed research programme on “Quantum Information Science and Technology (QuST)”. 
  • QuST promises to revolutionize the future computation and communication systems which will ultimately have a huge impact on the Nation and our society.
  • Broad Objectives of QuST:
    • Development and demonstration of quantum computers.
    • Development and demonstration of quantum communication & cryptography.
    • Development of quantum-enhanced and inspired technology.
    • Development of advanced mathematical quantum techniques, algorithms and theory of quantum information systems.

Challenges with Initiatives taken by government 

  • Policy gaps: India has loosely built quantum ecosystem where metrics to assess outcomes of its quantum efforts are not clearly defined. E.g., lack of target-oriented policies. 
  • Raising funds: Indian quantum computing startups struggle with funds for product development and scaling due to low venture capital investment. E.g., the budgeted R&D outlay is less than 1%.
  • Insufficient talent pool: India has small pool of researchers, industry professionals, academicians, and entrepreneurs as compared to China or the US. E.g., problem of brain-drain, inadequate infrastructure and research facilities.
  • Poor-infrastructure: India lacks in hardware manufacturing and still imports critical quantum components. India also lacks sufficient superconducting materials, semiconductor chips, processors, and fabrication labs.
  • R&D in silos: India lacks common platform for all quantum research and development. At present, research is carried out in silos and knowledge exchange is not structured. E.g., no common platform to transmit real-time data of research in quantum computing.
  • Lack of industry connection: Most quantum-related R&D is carried out in universities. While academia can provide well-researched prototypes; industry connection is essential for developing scalable applications.

Way Forward:

  • Rework Indian technology policy objectives, frameworks, and deliverables to move from importer of quantum technology to exporter.
  • Developing knowledge ecosystem by inculcating entrepreneurship, innovation, university courses, training programmes in quantum technology.
  • Develop metrics to assess success of strategy and short & long-term action plan.
  • Periodic feedback system to map progress of Quantum-Enabled Science and Technology initiatives.
  • Boost to investor ecosystem to amplify production of hardware components of quantum computer plus simultaneous push to semiconductor industry.

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