Using a 65-qubit Willow superconducting processor, Google researchers measured how quantum information spreads and refocuses within an entangled system. This technological leap in quantum computing was called Quantum Echoes.
Unlike the 2019 Sycamore experiment, which claimed “quantum supremacy” for completing a random-number task faster than any supercomputer, Quantum Echoes was not a speed race but a test of understanding. Scientists measured out-of-time-order correlators (OTOC) — tiny echoes that reveal how disturbances travel through a network of qubits.
The method resembles giving a material a microscopic “poke,” reversing time evolution, and listening for the returning echo. The echo’s strength reveals how quickly information disperses, offering insight for chemistry, materials science, and superconductivity. Despite its scientific importance, the experiment does not bring the world closer to breaking encryption or to Q-day.
“Harvest now, decrypt later”
Q-day refers to the day a cryptographically relevant quantum computer becomes powerful enough to break public-key encryption. It would not instantly expose all secrets, but any encrypted data stored today could be decoded later if intercepted now — a risk known as “harvest now, decrypt later.”
Governments and researchers are already preparing. The U.S. National Institute of Standards and Technology (NIST) has standardised new post-quantum cryptography (PQC) algorithms — CRYSTALS-Kyber for encryption and Dilithium for digital signatures. These rely on mathematical problems that are believed to resist both classical and quantum attacks.
Experts expect that machines capable of breaking RSA-2048 will need millions of logical qubits, which could take 5 to 8 years to build. [RSA-2048 is a commonly used standard for public-key cryptography.] Until then, Q-day remains a theoretical horizon, but one the cybersecurity world takes seriously.
Public-key cryptography secures nearly all online communication. RSA encryption works by multiplying two large prime numbers to create an enormous product. Multiplication is easy, but reversing it and finding the original primes is so difficult that even the fastest classical computers would need billions of years to solve it.
Machines that test multiple possibilities
Quantum computers operate under the laws of quantum mechanics. Their building blocks, called qubits, exploit superposition — the ability to exist as both 0 and 1 simultaneously — and entanglement — where qubits influence each other instantly, even when far apart. These features let quantum machines test many possibilities at once rather than sequentially.
This aspect of existing in multiple places at the same time powers Shor’s algorithm, which converts the hard task of factoring numbers into one of finding repeating patterns, or periods, in modular arithmetic. To expose those patterns, the algorithm uses the Quantum Fourier Transform (QFT), a mathematical tool that acts like a detector of hidden rhythms within a signal.
Scaling this method to large RSA numbers would let a quantum computer find their prime factors exponentially faster than classical machines.
Craig Gidney and Martin Ekera of Google Research estimated in 2019 that factoring a 2,048-bit RSA key would need about 20 million physical qubits and eight hours of computation, assuming perfect error correction. Current processors, such as Google’s Willow and IBM’s Condor, have only a few hundred noisy qubits.
A true fault-tolerant quantum computer would require millions of logical qubits, which are stable, error-corrected versions capable of long calculations. That scale remains far beyond present technology.
Shor’s algorithm and encryption systems
In theory, Shor’s algorithm is a computational tool designed to factor large numbers efficiently. Its purpose is mathematical and, eventually, cryptographic: it challenges the foundations of today’s encryption systems.
And Quantum Echoes is an experiment in physics. Instead of solving equations, it studies how quantum information spreads and re-emerges within entangled particles. While both — Shor’s algorithm and Quantum Echoes — use quantum hardware, they serve very different goals. Shor’s algorithm seeks computational advantage; Quantum Echoes seeks physical understanding.
So, the Willow experiment differs as its results can be verified through repeated measurements and signal-to-noise analysis. It represents progress in scientific reproducibility rather than in cryptographic power.
But experts caution that some entities may already be storing encrypted information today to decrypt in the future once quantum machines reach the necessary scale. To prepare, as mentioned earlier, the U.S. NIST has introduced post-quantum algorithms, while companies like Google and Cloudflare are adopting hybrid encryption to secure internet traffic.
Regulators, including India’s central bank, are urging organisations to transition to quantum-safe systems before the end of the decade. But most networks remain unprotected until that migration is complete.
How far is Q-Day?
So, what does this preparation by regulators and advances in quantum hardware tell us? Simply put, it will take a long time to break encryption using quantum computers. Google’s Quantum Echoes does not bring Q-day any closer. But it does mark a scientific milestone in understanding quantum behaviour.
The experiment shows that quantum processors can now verify complex physical interactions within entangled systems — a sign of maturity in quantum science rather than a cybersecurity threat.
As quantum technology evolves, its real promise may lie less in defeating today’s encryption and more in unlocking the secrets of nature itself. Ensuring our digital infrastructure evolves just as thoughtfully will determine how securely we enter the quantum era.
(Dr. Priti Kumari is a Research Analyst at a leading international asset management company)
Published – December 05, 2025 08:00 am IST