How a Quantum Computer Works

A quantum computer replaces the ordinary bit, a switch that is either zero or one, with a qubit: something that holds both at once until it is measured. This video explains what that actually means, why building one is so hard, and where the technology genuinely stands today.

First the mechanism: superposition, measurement, and entanglement, explained without the shortcuts that make the subject sound more mysterious than it is. Then the physical machine - superconducting qubits cooled near absolute zero, and decoherence, the fragility that has limited the field since it began.

Then the milestone: Google's Willow chip, reported in Nature on 9 December 2024, was the first real device where adding more physical qubits made the error rate go down rather than up - 'below the surface code threshold'. Its logical qubit lasted 2.4 times longer than its best individual physical qubit.

Then the plan: IBM's roadmap, published 10 June 2025, targets a machine called Starling for 2029 - 200 logical qubits, 100 million quantum operations - and a later machine, Blue Jay, with no date given.

And the contested claim: Microsoft's Majorana 1 chip, announced February 2025, claims a sturdier kind of qubit. Nature published a formal challenge to the evidence, echoing a near-identical claim from 2018 that was later retracted. This video reports it as contested, not settled - neither side has closed the question.

Finally, what any of this is actually for: a narrow set of problems with a known quantum algorithm, including factoring the large numbers behind today's internet encryption - the subject of this channel's companion video, 'The Quantum Threat to the Internet', which this video does not repeat.

No figure appears without its date, unit and source. A contested claim is presented as contested.

Educational documentary. Not financial or investment advice.