These claims make for compelling headlines, but they often blur the line between theoretical possibility and practical reality.

Yes, quantum computing has the potential to challenge many of today’s public-key cryptographic systems, including the elliptic curve cryptography used by Bitcoin. But moving from laboratory demonstrations involving hundreds or thousands of physical qubits to a fault-tolerant quantum computer capable of breaking Bitcoin is an enormous scientific and engineering leap.

The real story is far more nuanced than the headlines suggest. It involves quantum error correction, millions of high-quality physical qubits, cryptographic migration strategies, and a Bitcoin network that can evolve long before such machines become practical.

Before asking whether quantum computers will break Bitcoin, we should first ask a more fundamental question:

How close are we to building a quantum computer capable of doing so?

There are actually three different questions hidden inside “how many qubits have been held in coherence”:

1. How many physical qubits remained coherent simultaneously?
2. How many qubits were actually entangled together?
3. How long did the coherent quantum state survive?

These numbers are quite different.

The newest record

One of the most impressive demonstrations came from a Caltech-led team using neutral atoms.

They trapped

• 6,100 cesium atom qubits
• in nearly 12,000 optical tweezers
• while maintaining a measured hyperfine coherence time of 12.6 seconds—currently one of the best demonstrations of simultaneous large-scale coherence.

This is remarkable because earlier neutral-atom experiments typically involved hundreds of qubits, and scaling to thousands while preserving long coherence had been a major challenge.

Why this does not mean a 6,100-qubit quantum computer?

This is the important distinction.

Those 6,100 atoms were coherent qubits, but they were not all participating in one enormous quantum computation.

Maintaining coherence is only one ingredient.

You also need

• high-fidelity gates,
• entangling operations,
• measurements,
• quantum error correction,
• and repeated computation

without losing coherence.

That remains a much harder challenge.

Superconducting quantum computers

IBM and Google processors contain hundreds to over a thousand physical qubits, but their individual coherence times are much shorter:

• T₁ (energy relaxation): roughly 100–500 μs
• T₂ (phase coherence): typically 100–300 μs, depending on the device and qubit. These shorter times are offset by very fast gate operations (tens of nanoseconds), allowing many gate operations before decoherence becomes dominant.

Trapped ions

Trapped-ion systems are slower but much more stable.

Typical coherence times range from

• seconds
• to minutes

with dynamical decoupling.

Some isolated ion qubits have maintained coherence for minutes or longer under laboratory conditions.

Why scaling is so difficult

Suppose every qubit has only a 0.001% chance of decohering during a computation.

For

• 10 qubits, the probability that all survive is still very high.
• 1,000 qubits, the probability that every qubit remains coherent drops substantially.
• 1,000,000 qubits, it becomes vanishingly small without continuous quantum error correction.

That is why researchers often say the challenge is not creating qubits—it is keeping millions of them synchronized long enough to perform useful computation.

This is the central engineering obstacle on the path to large-scale, fault-tolerant quantum computers.

The post Decoherence -The challenge to scale any realistic quantum computer appeared first on Bitcoin Physics - Bitcoin - Nature's 5th Fundamental Force.