In News:

Recent advances in Quantum Error Correction (QEC) by companies such as Google, coupled with progress under India's National Quantum Mission (NQM), have renewed global interest in quantum computing. These developments are expected to accelerate the transition from today's Noisy Intermediate-Scale Quantum (NISQ) systems to fault-tolerant quantum computers, unlocking transformative applications in cryptography, climate modelling, drug discovery and materials science.

What is Quantum Computing?

Quantum computing is an emerging field that harnesses the principles of quantum mechanics to solve computational problems that are beyond the practical capabilities of classical computers. Unlike classical computers, which process information using bits that exist either as 0 or 1, quantum computers use quantum bits (qubits). Owing to quantum phenomena such as superposition and entanglement, qubits can process multiple possibilities simultaneously, enabling exponential speed-ups for certain classes of problems.

Principles of Quantum Computing

Quantum computing relies on three fundamental principles.

• Superposition: A qubit can exist in multiple states simultaneously until it is measured, allowing parallel computation.
• Entanglement: Two or more qubits become intrinsically linked so that the state of one is correlated with the other, regardless of the distance between them.
• Interference: Quantum algorithms amplify correct computational paths while cancelling incorrect ones, improving the probability of obtaining the right solution.

Together, these principles enable massive parallelism, making quantum computers particularly powerful for optimisation, simulation and cryptographic applications.

Types of Qubits

Several physical technologies are being explored for building quantum computers.

• Superconducting qubits – Based on Josephson junctions operating at temperatures close to absolute zero (used by Google's Willow processor).
• Quantum Dot qubits – Semiconductor-based qubits made from materials such as silicon or germanium.
• Trapped Ion qubits – Individual charged atoms confined using electromagnetic fields.
• Photonic qubits – Encode quantum information using photons.
• NMR qubits – Based on nuclear spins and used in the first quantum computer demonstration in 1998.

Quantum Key Distribution (QKD)

Quantum Key Distribution (QKD) is a secure communication technique that uses quantum properties of photons to exchange encryption keys. Any attempt to intercept the communication disturbs the quantum state, immediately revealing the presence of an eavesdropper. This makes QKD one of the most secure methods for transmitting cryptographic keys.

The Noise Problem in Quantum Computing

The biggest challenge in quantum computing is decoherence, where interactions with the surrounding environment—such as heat, electromagnetic radiation or vibration—destroy the fragile quantum state of qubits.

Current NISQ devices remain highly error-prone despite operating at temperatures close to absolute zero (-273°C). Their error rates remain significantly higher than those of classical computers. In addition, imperfections in lasers, microwave pulses and control systems introduce further computational errors.

Quantum Error Correction (QEC)

Quantum Error Correction (QEC) is a technique that combines multiple physical qubits to create a more reliable logical qubit capable of preserving quantum information despite individual errors.

A major breakthrough occurred when researchers demonstrated that once the error rate of physical qubits falls below a critical threshold, increasing the number of qubits actually reduces the overall error rate instead of increasing it. Google's Willow processor demonstrated this principle by successfully suppressing encoded errors, marking an important step towards practical fault-tolerant quantum computers.

India's National Quantum Mission (NQM)

The National Quantum Mission (NQM) was approved by the Government of India in April 2023 with the objective of making India a global leader in quantum technologies by 2031.

The mission seeks to develop intermediate-scale quantum computers with 50–1,000 qubits, establish a 2,000-km satellite-based quantum communication network, deploy Quantum Key Distribution (QKD) systems, advance quantum sensing and metrology, and promote indigenous development of quantum materials, devices, hardware and software.

To accelerate innovation, the mission has established four Thematic Hubs (T-Hubs) and supports quantum start-ups through innovative financing mechanisms such as Optionally Convertible Debt (OCD).

India has already achieved a significant milestone by developing an indigenous 1,000-km quantum communication network through the Department of Science and Technology (DST) in collaboration with QNu Labs, achieving half of its long-term communication target.

In News:

In a landmark experiment, researchers have successfully demonstrated a method to create perfect copies of quantum states by navigating a technical loophole in the No-Cloning Theorem. This discovery addresses one of the most significant bottlenecks in quantum information science, offering a blueprint for resilient quantum cloud storage and more reliable quantum memories.

The Fundamental Constraint: The No-Cloning Theorem

• The Rule: In quantum mechanics, the No-Cloning Theorem states that it is physically impossible to create an identical, independent copy of an arbitrary, unknown quantum state.
• The Mechanism: Unlike classical bits (0 or 1), which can be copied infinitely without degradation, quantum bits (qubits) exist in a state of superposition. The act of measuring or observing a quantum state causes its "wavefunction" to collapse, effectively destroying the original information.
• Significance: This theorem is the bedrock of Quantum Cryptography (e.g., Quantum Key Distribution), as it ensures that any attempt by an eavesdropper to copy or intercept data will be instantly detectable.

The Breakthrough: The "Noise Encryption" Loophole

The researchers did not "break" the laws of physics but rather utilized a sophisticated encryption method to store quantum information across multiple locations simultaneously.

1. Individual Encryption with Quantum Noise

The team established that perfect copies can be created if each clone is individually "masked" or encrypted using quantum noise.

• Noise Qubits: Special qubits act as "locking patterns." They store the noise signature used to encrypt the clones.
• Security: Without the corresponding decryption key (the noise pattern), a clone appears to be meaningless, random data. This ensures that even if a copy is intercepted, the underlying information remains naturally secure.

2. Distributed Information

• The original quantum information is not residing in a single qubit but is spread across multiple qubits. To an outside observer, each qubit looks like random noise; only the holder of the key can reconstruct the perfect state.

1. The "One-Time Use" Constraint

Crucially, the method adheres to the spirit of quantum mechanics through a self-destruct mechanism:

• Key Destruction: Once a decryption key is utilized to recover one perfect copy, the key is permanently destroyed.
• Irreversibility: All other existing clones immediately become unreadable and useless.
• Result: While multiple "potential" copies exist, only one can ever be successfully recovered, maintaining the fundamental "uniqueness" required by quantum laws.

Strategic Applications & Future Infrastructure

This achievement has transformative implications for the future of the "Quantum Internet" and digital infrastructure:

• Quantum Cloud Storage: Clients can store data across multiple servers (redundancy). Even if several servers fail or are destroyed, the client can recover the perfect data as long as one server and the decryption key survive.
• Reliable Quantum Memories: It provides a method for backing up fragile quantum information, which is currently prone to "decoherence" (data loss due to environmental interference).
• Resilient Quantum Networks: Enhances the robustness of quantum communication channels against hardware failures.

In News:

NITI Ayog releases strategic paper on implication of quantum computing on national security.

What is Quantum Computing?

Quantum computing utilizes quantum bits (qubits), which leverage the principles of superposition and entanglement, enabling them to exist in multiple states simultaneously. Unlike classical bits (0 or 1), qubits can perform parallel computations, exponentially increasing processing power.

Global Landscape and India's Position

• Global Investments: Over $40 billion invested by 30+ nations.
  • China: $15 billion (leader)
  • USA and EU: Close followers
• India: Launched the National Quantum Mission (NQM) in 2023 with a budget of ?6,003 crore (~USD 750 million) to boost indigenous capabilities in computing, cryptography, communication, and sensing.

National Quantum Mission (NQM): Key Highlights

• Timeframe: 2023–2031
• Quantum Computers: Build systems with 50–1000 physical qubits using superconducting, photonic, and other platforms
• Secure Communication: Satellite-based secure quantum links over 2000 km within India and long-distance secure communication with other nations
• Quantum Sensing & Metrology: Development of precision navigation tools like atomic clocks and magnetometers
• Thematic Hubs (T-Hubs): To be established in premier R&D institutes in four domains:
  • Quantum Computing
  • Quantum Communication
  • Quantum Sensing & Metrology
  • Quantum Materials & Devices

Quantum Technology in Defence& National Security

• Cybersecurity
  • Existing encryption standards will become obsolete.
  • Urgent need for Post-Quantum Cryptography (PQC) to protect critical digital infrastructure.
• Signals Intelligence (SIGINT) & Espionage
  • Quantum computers can decrypt communications at scale, risking exposure of classified diplomatic and military data.
  • Enables real-time data processing for advanced surveillance.
• Military Applications
  • Quantum materials improve stealth detection and weapon precision.
  • Enhances autonomous weapons and navigation in GPS-denied environments.
• Logistics & Planning: Quantum AI can optimize defence logistics, battlefield resource allocation, and strategic decision-making.
• Economic Security: Quantum computing can protect or exploit vulnerabilities in financial systems, posing potential risks to economic stability.

Challenges for India

• Funding Gap: India’s allocation is modest compared to global peers.
• Hardware Dependence: Relies on imports for cryogenic systems, high-purity materials, and specialized lasers.
• Limited Industry Participation: India's ecosystem is academia-driven, with limited private sector engagement.
• Cybersecurity Risk: Legacy systems vulnerable to quantum attacks.
• Talent Shortage: Lack of trained quantum scientists and engineers.
• Geopolitical Race: Export restrictions by advanced countries can limit India’s access to key technologies.

Recent Advances in Quantum Technology

• Atom Computing/ColdQuanta: Improved qubit coherence for stable computations.
• IBM/Quantinuum: Enhanced qubit control and error reduction.
• Google Willow Chip: Introduced self-correcting qubit system.
• Microsoft Majorana-1: Developed topological qubits to improve fault tolerance.

Recommendations by NITI Aayog

• Policy & Preparedness:
  • Form a National Quantum Task Force to monitor global trends and threats.
  • Develop an Early Warning System for quantum vulnerabilities.
  • Implement a PQC Transition Plan across critical sectors.
• R&D & Startups:
  • Increase funding to scale quantum startups and indigenous hardware.
  • Promote public-private partnerships to commercialize academic research.
• Supply Chain Development:Invest in domestic manufacturing for quantum components like chips and lasers.
• Global Engagements:
  • Strengthen partnerships with the US, EU, and Japan.
  • Advocate for easing export controls to access vital technologies.