Executive Summary
The Story So Far
Why This Matters
Who Thinks What?
IBM researchers have achieved a significant milestone in quantum computing, successfully creating and entangling a 120-qubit quantum state, a new benchmark for stability and scale. This breakthrough, detailed in a report titled “Big Cats: Entanglement in 120 Qubits and Beyond” published earlier this month, demonstrates genuine multipartite entanglement across all qubits, pushing the theoretical frontier closer to developing fault-tolerant quantum computers capable of potentially cracking modern cryptography, including Bitcoin’s encryption.
Quantum Breakthrough Details
The IBM team utilized a class of quantum states known as Greenberger–Horne–Zeilinger (GHZ) states, often referred to as “cat states” in reference to Schrödinger’s famous thought experiment. A GHZ state represents a system where every qubit exists in a superposition of all being zero and all being one simultaneously, meaning a change in one qubit affects all others—a phenomenon impossible in classical physics.
These GHZ states are considered highly sensitive benchmarks for quantum platforms due to their extreme vulnerability to experimental imperfections. To achieve the 120-qubit entanglement, IBM researchers employed superconducting circuits, an adaptive compiler that optimized operations to the least noisy regions of the chip, and a process called temporary uncomputation, which momentarily disentangles qubits when their role is complete to allow them to rest in a stable state before reconnection.
Verifying Quantum Entanglement
The quality of the quantum state was measured using fidelity, a metric that gauges how closely the produced state matches the ideal mathematical state. A fidelity score of 0.5 is the minimum threshold to confirm full quantum entanglement, and IBM’s 120-qubit GHZ state achieved a fidelity of 0.56, validating that all qubits remained part of a single, coherent system.
Directly verifying such a complex state is computationally infeasible, requiring more time than the age of the universe. Instead, IBM utilized statistical shortcuts, including parity oscillation tests to track collective interference patterns and Direct Fidelity Estimation, which involves randomly sampling a subset of the state’s measurable properties called stabilizers. Each stabilizer serves as a diagnostic tool, confirming whether pairs of qubits maintain their synchronized state.
Implications for Bitcoin Security
While still theoretical, IBM’s advancement contributes to the growing concern regarding quantum threats to existing cryptographic standards. The report highlights that a sufficiently powerful quantum computer could, in theory, compromise the roughly 6.6 million Bitcoin—valued at approximately $767.28 billion—that are currently vulnerable to quantum attacks, including those held by Bitcoin creator Satoshi Nakamoto.
According to Alex Pruden, founder of quantum computing research group Project 11, once a Bitcoin address exposes its public key, a powerful quantum computer could potentially reconstruct the private key and seize funds before transaction confirmation. Pruden noted the dilemma this presents for Satoshi’s coins, stating, “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 Road Ahead
This breakthrough follows Google Quantum AI’s recent achievement with its 105-qubit Willow chip, which ran a physics algorithm faster than any classical computer could simulate, demonstrating a confirmed quantum advantage. Such rapid progress from major tech firms like IBM and Google, alongside companies like Quantinuum, signals an accelerating timeline for the development of fault-tolerant quantum computers.
With IBM targeting fault-tolerant systems by 2030, the potential for quantum computers to impact digital assets, particularly those relying on older cryptographic schemes like Bitcoin’s ECDSA, is becoming an increasingly tangible long-term concern for the cryptocurrency landscape.
