BT Explainer: What is quantum computing, why it matters and how India is building it

Quantum computing is often described as the next big leap in computing, but the idea can feel abstract. At its core, it is a new way of processing information, one that uses the laws of quantum mechanics, the physics that governs the smallest particles in the universe.

Unlike traditional computers, which follow clear, predictable rules, quantum systems behave in ways that seem counterintuitive. That is precisely what gives quantum computing its power.

What is quantum computing?

Quantum computing is a field of computer science that uses quantum mechanics to solve problems that are too complex for classical computers. Instead of processing information in simple binary form, zeros and ones, it uses quantum bits, or qubits.

A classical computer works step by step. Meanwhile, a quantum computer can explore many possible solutions at once. This allows it to tackle certain types of problems, such as simulating molecules, optimising complex systems or analysing large datasets, much faster.

In theory, tasks that would take today’s most powerful supercomputers thousands of years could be solved by quantum machines in minutes or hours.

Bits vs qubits 

The biggest shift in quantum computing comes from how information is stored. A classical bit can be either 0 or 1. A qubit, however, can exist in a combination of both at the same time. This is made possible by a principle called superposition.

Think of it this way: a classical computer explores one path at a time, while a quantum computer can evaluate multiple paths simultaneously. As more qubits are added, the number of possible states grows exponentially, making the system far more powerful for certain tasks.

To understand quantum computing, a few key ideas matter.

• Superposition allows a qubit to be in multiple states at once until it is measured. This dramatically expands the amount of information a system can handle.
   
• Entanglement is a phenomenon where qubits become linked. When one changes, the other reflects that change instantly, even across distances. This enables coordinated computation across qubits.
   
• Interference helps amplify the correct answers and cancel out incorrect ones. It is how quantum algorithms narrow down possibilities.
   
• Decoherence is the challenge. Quantum states are extremely fragile and can collapse due to environmental noise, which is why quantum systems require highly controlled conditions.

Why quantum computers are hard to build

Quantum computers are not just faster versions of existing machines. They require entirely new hardware.

Most quantum processors operate at temperatures close to absolute zero, around minus 273 degrees Celsius. At these temperatures, materials behave differently, allowing qubits to maintain their quantum state.

The systems are large, complex and sensitive. Even small disturbances can disrupt calculations. This is why much of the work in quantum computing today is focused on stabilising hardware and improving error correction.

Where quantum computing could be used

Quantum computing is not meant to replace classical computers. Instead, it will work alongside them, handling specific types of problems.

One major area is chemistry and material science. Quantum systems can simulate molecules more accurately, helping in drug discovery and new material design.

Another is optimisation, improving logistics, financial modelling or energy systems.

There is also growing interest in machine learning, where quantum algorithms could process complex datasets in new ways.

At the same time, quantum computing has serious implications for cybersecurity. Some quantum algorithms could break current encryption systems, which is why “quantum-safe” security is becoming a priority.

India’s push: National Quantum Mission

India has begun investing heavily in quantum technology through the National Quantum Mission. Approved in 2023 with an outlay of over Rs 6,000 crore, the mission aims to build capabilities across quantum computing, communication, sensing and materials. The goal is to develop intermediate-scale quantum computers with 50 to 1,000 qubits over the next eight years.

The mission also focuses on secure communication networks using quantum key distribution, which is considered virtually unhackable. India has already demonstrated a 1,000-km quantum communication network using indigenous technology, a significant milestone.

Beyond infrastructure, the mission is designed to support startups and build a domestic ecosystem, reducing dependence on foreign technology.

Amaravati’s open quantum labs

One of the most notable recent developments is the launch of India’s first open-access quantum test beds in Andhra Pradesh.

Built under the Amaravati Quantum Valley initiative, the facilities at SRM University and Medha Towers allow researchers, startups and students to work directly with quantum hardware. 

This is a departure from global norms, where most quantum systems are locked inside specialised labs. The Amaravati facilities are designed to be modular and accessible, allowing components to be tested, replaced and improved.

The idea is to lower the barrier to entry and accelerate innovation. By sourcing components domestically, developers have also managed to reduce costs significantly.

QpiAI and the rise of Indian quantum hardware

India is also seeing early moves in quantum hardware development.

Bengaluru-based QpiAI recently launched “Kaveri,” a 64-qubit superconducting quantum processor. It is currently one of the most powerful quantum systems built in the country and is expected to be commercially available soon.

The processor is designed for applications in cryptography, optimisation and machine learning, aligning with global use cases for quantum systems.

This follows earlier milestones such as IISc’s six-qubit photonic system, indicating that India is gradually building capabilities across different quantum platforms.

A long-term bet 

Quantum computing is still in its early stages. Most systems today are experimental and large-scale, fault-tolerant quantum computers are still years away. Governments and companies worldwide are investing heavily, betting that quantum computing will unlock breakthroughs across industries.

For India, the focus is not just on catching up but building a self-reliant ecosystem, from hardware and software to talent and applications.