THE HISTORY OF COMPUTING is a history of conquering noise. In the earliest vacuum tube computers, noise was heat that caused tubes to fail. In silicon transistors, it was quantum tunnelling that set the floor on how small a device could be. In quantum computers, noise is something more fundamental and more vexing: it is the universe’s intrinsic tendency to destroy the fragile superposition states on which quantum computation depends. For three decades, this noise — called decoherence — has been the primary barrier between quantum computing’s extraordinary theoretical promise and practical, real-world utility. In 2025 and early 2026, the scientific community has crossed a threshold that researchers have been working toward since Peter Shor first proposed fault-tolerant quantum computation in 1995.
The threshold in question is called the error-correction threshold. Below this threshold, adding more physical qubits to an error-correcting code makes things worse — the additional complexity introduces more errors than it corrects. Above this threshold, adding qubits exponentially suppresses errors, and the logical qubit — the virtual, error-protected qubit built from many physical ones — becomes progressively more reliable as the system scales. For the first time, multiple independent research teams around the world have demonstrated below-threshold operation across different hardware architectures.
Google’s Willow: Setting the Benchmark
The watershed demonstration came from Google Quantum AI in late 2024 with its 105-qubit Willow processor, published in Nature. Using surface codes — a two-dimensional grid of physical qubits that can detect and correct errors by measuring parity rather than state directly — the Willow team achieved a distance-7 logical qubit whose lifetime exceeded that of its best single physical qubit by a factor of 2.4. Crucially, when the code distance was increased from 5 to 7, the logical error rate decreased rather than increased — the defining signature of below-threshold performance. The error suppression factor Λ reached 2.14, meaning each step up in code distance more than doubled the reliability of the logical qubit.
This result was quickly followed by parallel demonstrations on other platforms. China’s University of Science and Technology of China validated below-threshold operation on its 107-qubit Zuchongzhi 3.2 processor using an ‘all-microwave control’ architecture that represents a technically distinct pathway from Google’s approach. IBM reported record fidelity for entangled logical qubits on its superconducting hardware in early 2026. Oxford physicists achieved single-qubit gate error rates below 1 in 10 million — entering what the community calls ‘seven nines’ fidelity — using trapped ions.
The Neutral Atom Breakthrough
Perhaps the most significant architectural advance came from the neutral-atom platform championed by QuEra Computing, in collaboration with Harvard, MIT, and Yale. In a series of four landmark papers published in Nature in 2025, the Harvard-MIT collaboration demonstrated: a 3,000-qubit neutral-atom array operating continuously for over two hours with mid-computation atom replenishment; an integrated fault-tolerant architecture executing algorithms with 96 logical qubits; the first logical magic state distillation (necessary for universal quantum algorithms); and a framework called Transversal Algorithmic Fault Tolerance that reduces error-correction overhead by 10 to 100 times. These results collectively resolved what had been considered the four major engineering barriers to scaling neutral-atom quantum computers.
The significance of 96 logical qubits running in a fault-tolerant architecture cannot be overstated. To be commercially useful — for drug discovery, materials simulation, cryptography, or financial optimisation — a quantum computer needs thousands of high-quality logical qubits running deep circuits. The current generation demonstrates that the physics works. The challenge now is an engineering execution problem: manufacturing, control electronics, cryogenic infrastructure, and software. QuEra closed over $230 million in financing in late 2025, led by Google Quantum AI and SoftBank Vision Fund 2, with additional investment from NVIDIA’s venture arm — a convergence of the world’s leading compute companies on a single quantum platform.
What Error Correction Actually Means for Applications
The shift from noisy intermediate-scale quantum (NISQ) devices — which are the current generation, doing their best without error correction — to fault-tolerant quantum computers (FTQCs) is not merely an incremental improvement. It is a categorical transition. NISQ devices can perform certain narrow tasks faster than classical computers, but their noise floor limits circuit depth, and therefore the complexity of problems they can address. FTQCs can, in principle, run arbitrarily deep circuits on arbitrarily complex problems, as long as sufficient logical qubits are available.
The applications waiting on the other side of this transition are transformative. In pharmaceuticals, fault-tolerant quantum simulation of molecular dynamics could make drug discovery orders of magnitude faster and more precise than current computational chemistry allows. In materials science, quantum simulation of superconducting and catalytic materials could accelerate the development of room-temperature superconductors and next-generation battery chemistries. In logistics and finance, quantum optimisation algorithms could solve combinatorial problems — routing, portfolio management, supply chain design — that are computationally intractable for classical machines.
India’s Position in the Quantum Race
India launched its National Quantum Mission in 2023 with a budget of ₹6,003 crore over eight years, targeting development of intermediate-scale quantum computers, quantum communication networks, and quantum sensing platforms. Institutions including IISc Bangalore, IIT Bombay, TIFR, and C-DAC are active in quantum hardware and software research. The global breakthrough in error correction provides both an opportunity and an urgency signal: the window for establishing domestic quantum hardware capability is narrowing as the international field consolidates. India’s academic strength in quantum physics and its expanding semiconductor ecosystem — anchored by the new Tata and Micron fabrication investments — create a plausible pathway to competitive quantum hardware manufacturing if policy and investment move decisively in the next three to five years.
– V Murali Krishna
