Google claims to have achieved a major breakthrough with "quantum supremacy". But what could quantum computers actually do, and how soon will they be useful?

Manuela Saragosa speaks to Harvard quantum computing researcher Prineha Narang, who says that the devices she is working on are annoyingly "noisy", but could still make an important contribution to tackling climate change in the next few years.

There are fears that quantum computers could one day crack modern encryption techniques - rendering private communications and financial transactions unsafe. But IBM cryptography researcher Vadim Lyubashevsky says don't worry, they've got the problem in hand.

Plus, the BBC's technology correspondent Rory Cellan-Jones delineates the greatest paradox of quantum computers - that nobody can explain how they work.

Producer: Laurence Knight

(Picture: Engineer working on IBM Q System One quantum computer; Credit: Misha Friedman/Getty Images)