Quantum Computing | Science & Technology for UPSC CSE PDF Download

Introduction

Quantum computing represents a paradigm shift in computational technology, leveraging the principles of quantum mechanics to perform calculations that are infeasible for classical computers. Unlike traditional computing, which relies on binary bits, quantum computing uses quantum bits or qubits that can exist in multiple states simultaneously, enabling exponential processing power for complex problems. As of 2025, quantum computing is transitioning from theoretical research to practical applications, with global investments surpassing trillions of dollars. In India, the National Mission on Quantum Technologies and Applications (NM-QTA), now known as the National Quantum Mission (NQM), is a flagship initiative driving indigenous development. Launched in 2023 with a budget of ₹6,003.65 crore, the mission aims to position India as a global leader in quantum technologies by 2031. 

Fundamentals of Quantum Computing

Quantum computing harnesses the laws of quantum mechanics to solve problems too complex for classical computers. It differs fundamentally from classical computing, where bits represent either 0 or 1. In quantum systems, information is processed using qubits, which can represent multiple states at once due to quantum properties.

• Qubits vs. Bits: A classical bit is binary (0 or 1), while a qubit can exist in a superposition of states, allowing it to perform multiple calculations simultaneously. Qubits are physical systems like superconducting circuits, trapped ions, photons, or quantum dots.
• Quantum States: Qubits are described by probability amplitudes in a complex vector space. The state of a qubit is represented as |ψ⟩ = α|0⟩ + β|1⟩, where |α|² + |β|² = 1, and α and β are complex numbers determining the probability of measuring 0 or 1.
• Scalability: A system with n qubits can represent 2^n states simultaneously, enabling exponential growth in computational power. For example, 100 qubits could theoretically process more states than atoms in the observable universe.

Key Principles of Quantum Mechanics in Computing

Quantum computing relies on counterintuitive principles that defy classical physics, enabling superior problem-solving capabilities.

• Superposition: Qubits can exist in multiple states at once, unlike classical bits. This allows quantum computers to evaluate many possibilities simultaneously, dramatically speeding up algorithms like Grover's for database searches.
• Entanglement: When qubits become entangled, the state of one instantly influences another, regardless of distance. This correlation enables complex computations, such as in Bell states for secure communication.
• Interference: Quantum states can amplify or cancel each other, allowing algorithms to reinforce correct solutions while eliminating errors. This is crucial for quantum algorithms like Shor's for factoring large numbers.
• Decoherence: External noise causes quantum states to collapse, introducing errors. Mitigating decoherence through error correction and cryogenic cooling is a major challenge.
• Measurement: Observing a qubit collapses its superposition to a definite state (0 or 1), following the Born rule for probabilities.

How Quantum Computers Work

Quantum computers process information through quantum circuits, where qubits are manipulated using gates and measured to extract results.

• Components: Include qubits (e.g., superconducting loops), quantum gates (e.g., Hadamard for superposition, CNOT for entanglement), circuits (sequences of gates), measurements (to collapse states), and hardware (cryogenic systems for stability).
• Process: Initialize qubits in superposition, apply gates to entangle and interfere states, and measure to obtain probabilistic outputs. Algorithms like Shor's exploit this for exponential speedups in factorization.
• Types of Qubits: Superconducting (fast but noisy), trapped ions (stable but slow), photonic (scalable for communication), and others.
• Advantages: Solve intractable problems (e.g., simulating molecules) exponentially faster than classical systems.
• Limitations: High error rates, scalability issues, and enormous energy requirements for cooling to near-absolute zero.

Applications of Quantum Computing

Quantum computing promises breakthroughs across sectors by tackling optimization, simulation, and encryption challenges.

• Healthcare: Accelerate drug discovery by simulating molecular interactions, enabling personalized medicine.
• Finance: Optimize portfolios, detect fraud, and model risks with quantum machine learning.
• Materials Science: Design new materials like superconductors for energy efficiency.
• Cryptography: Break RSA encryption (Shor's algorithm) but enable quantum-secure methods.
• AI and Optimization: Enhance machine learning for pattern recognition and solve logistics problems.

Global Developments in Quantum Computing

As of 2025, quantum computing is a $1.3 trillion industry, with major powers racing for supremacy.

• United States: IBM and Google lead with systems like Sycamore (quantum supremacy in 2019). Investments exceed $6.9 billion.
• China: Leads in patents (40% global share), with $15.3 billion invested and operational systems like Jiuzhang.
• Europe: EU's Quantum Flagship invests €1 billion; focus on hybrid systems.
• Milestones: IBM's 433-qubit Osprey; Google's error-corrected logical qubits in 2025.

India’s Initiatives in Quantum Computing

India's quantum journey began with the 2018 Quantum Enabled Science and Technology (QuEST) program, evolving into the NQM in 2023.

• National Quantum Mission (NQM): Approved in April 2023 with ₹6,003.65 crore for 2023–2031, implemented by DST. Aims: Develop 50–1,000 qubit computers, secure communications over 2,000 km, quantum sensors, and materials.
• Thematic Hubs (T-Hubs): Four hubs: Quantum Computing (IISc Bengaluru), Communication (IIT Madras), Sensing & Metrology (IIT Bombay), Materials & Devices (IIT Delhi).
• Key Projects: 100-qubit superconducting facility at C-DAC Bengaluru (₹70–80 crore, scalable to 250 qubits); Quantum Simulator Toolkit (QSim); I-HUB QTF at IISER Pune.
• Collaborations: With AWS for Quantum Computing Applications Lab; DRDO for QKD demonstrations.
• Startups and Industry: 53 startups (6th globally); QpiAI's 25-qubit Indus system in 2025.

Recent Developments in India

India's quantum ecosystem has accelerated in 2025, with multiple milestones under NQM.

• Calls for Proposals: Extended deadline to 2025, for quantum algorithms; rolling call for startups in computing, communication, sensing, and materials.
• Events and Facilities: Quantum Quest 2025 at IIT Kanpur (March); 100-qubit facility procurement at C-DAC; Quantum India Bengaluru Summit (July–August).
• Technological Milestones: QpiAI's 25-qubit superconducting system (April); 6-qubit processor testing by DRDO and TIFR (August 2024, operational in 2025).
• Policy and Investments: International Technology Engagement Strategy for Quantum (ITES-Q) launched (April); ₹600 crore boost in Budget 2025.

Challenges and Ethical Issues

Despite progress, quantum computing faces significant hurdles.

• Technical: Decoherence, error rates, scalability; India lags in infrastructure and skilled workforce (only 50,000 experts needed by 2030).
• Economic: High costs; India ranks 12th in public investment ($735 million).
• Ethical: Breaks current encryption, risking data security; potential for unequal access exacerbating digital divides.
• Regulatory: Need for quantum-resistant standards; dual-use risks in defense.

Quantum computing, grounded in superposition and entanglement, offers unprecedented computational power for solving global challenges. India's NQM, with its hubs and 2025 advancements like the 25-qubit system, positions the country for quantum leadership. As of August 2025, sustained investments and collaborations are essential to overcome challenges and realize applications in healthcare, finance, and security, aligning with Atmanirbhar Bharat for sustainable development.