The summary.
QUANTUM COMPUTERS ARE NOT FASTER CLASSICAL COMPUTERS
They may solve specific classes of problem faster. Measurement yields one probabilistic outcome, so algorithms must be built so wrong answers cancel.
Be sceptical of any product claiming quantum capability without naming the problem class.
QUBIT COUNTS ALONE SAY ALMOST NOTHING
Error rates and logical qubit counts say more. Error correction needs hundreds or thousands of physical qubits per reliable logical one.
THE STRONGEST APPLICATION IS SIMULATING QUANTUM SYSTEMS
Chemistry, materials and molecules. The optimisation claims are far less settled, and several have been matched by improved classical methods.
DISTINGUISH QUANTUM CRYPTOGRAPHY FROM POST-QUANTUM CRYPTOGRAPHY
The first uses quantum effects and needs special hardware over limited distances. The second is classical algorithms resistant to quantum attack — and is what actually concerns most organisations.
DATA CAPTURED TODAY MAY BE DECRYPTED LATER
Which is why anything with a long secrecy requirement is already exposed. Inventory where public-key cryptography is used, and prefer systems that can change algorithms without redesign.
