IBM’s 120-Qubit Breakthrough Threatens Bitcoin Security

IBM researchers have created the most significant and stable 120-qubit entangled quantum state to date, surpassing Google Quantum AI’s recent 105-qubit Willow chip achievement. The experiment, detailed in the paper “Big Cats: Entanglement in 120 Qubits and Beyond,” demonstrates genuine multipartite entanglement across all qubits—a critical advancement toward fault-tolerant quantum computers. The team used techniques from graph theory, stabilizer groups, and circuit uncomputation to achieve this quantum milestone.

The IBM team employed Greenberger-Horne-Zeilinger (GHZ) states, commonly known as “cat states” after Schrödinger’s famous thought experiment. These states represent systems where every qubit exists in a superposition of all being zero and all being one simultaneously, creating a scenario where if one qubit changes, they all do—a phenomenon impossible in classical physics. To reach 120 qubits, researchers used superconducting circuits and an adaptive compiler that mapped operations to the least noisy regions of the chip, along with temporary uncomputation that allowed qubits to rest in stable states before reconnection.

The quality of the quantum state was measured using fidelity, with IBM’s 120-qubit GHZ state achieving a fidelity of 0.56—surpassing the 0.5 threshold required to confirm full quantum entanglement. This proves that every qubit remained part of a single, coherent system. Direct verification of such results would be computationally impossible through conventional means, as testing all configurations of 120 qubits would take longer than the age of the universe.

IBM employed sophisticated statistical methods to verify their quantum achievement, using parity oscillation tests that track collective interference patterns and Direct Fidelity Estimation, which randomly samples a subset of the state’s measurable properties called stabilizers. Each stabilizer acts as a diagnostic tool, confirming whether pairs of qubits remain synchronized. This approach offers scalable quantum verification that could be crucial for future, larger-scale quantum systems.

The researchers noted that GHZ states have historically served as benchmarks across various quantum platforms including ions, superconductors, neutral atoms, and photons. These states are extremely sensitive to experimental imperfections and can be used to achieve quantum sensing at the Heisenberg limit—the ultimate boundary for measurement precision in quantum physics. IBM’s success with 120 qubits demonstrates significant progress in controlling quantum systems at scale.

While IBM’s 120-qubit system cannot currently break Bitcoin’s encryption, the breakthrough represents a meaningful step toward that capability. According to quantum computing research group Project 11, approximately 6.6 million BTC—worth about $767.28 billion—remains vulnerable to future quantum attacks. This includes coins owned by Bitcoin creator Satoshi Nakamoto, whose identity and whereabouts remain unknown.

Project 11 founder Alex Pruden highlighted the dilemma surrounding Satoshi’s coins in comments to Decrypt: “This is one of Bitcoin’s biggest controversies: what to do with Satoshi’s coins. You can’t move them, and Satoshi is presumably gone. So what happens to that Bitcoin? It’s a significant portion of the supply. Do you burn it, redistribute it, or let a quantum computer get it? Those are the only options.”

The quantum threat emerges when a Bitcoin address exposes its public key, creating a vulnerability that a sufficiently powerful quantum computer could exploit to reconstruct the private key and seize funds before transaction confirmation. With IBM targeting fault-tolerant quantum systems by 2030, and competitors like Google and Quantinuum pursuing similar goals, the timeline for quantum threats to digital assets is becoming increasingly tangible. The race to develop quantum-resistant cryptography is now more urgent than ever as quantum computing capabilities continue to advance.