Quantum computing is a tough subject to explain and discuss. As Niels Bohr put it, “Anyone who is not shocked by quantum theory has not understood it”. Richard Feynman helpfully added, “I think I can safely say that nobody understands quantum mechanics”.Quantum computing employs the weird properties of quantum mechanics like superposition and entanglement. Classical computing uses binary digits, or bits, which are either on or off. Quantum computing uses qubits, which can be both on and off at the same time, and this characteristic somehow makes them enormously more computationally powerful.Co-hosts Calum and David knew that to address this important but difficult subject, we needed an absolute expert, who was capable of explaining it in lay terms. When Calum heard Dr Ignacio Cirac give a talk on the subject in Madrid last month, he knew we had found our man.Ignacio is director of the Max Planck Institute of Quantum Optics in Germany, and holds honorary and visiting professorships pretty much everywhere that serious work is done on quantum physics. He has done seminal work on the trapped ion approach to quantum computing and several other aspects of the field, and has published almost 500 papers in prestigious journals. He is spoken of as a possible Nobel Prize winner.Topics discussed in this conversation include:*) A brief history of quantum computing (QC) from the 1990s to the present*) The kinds of computation where QC can out-perform classical computers*) Likely timescales for further progress in the field*) Potential quantum analogies of Moore's Law*) Physical qubits contrasted with logical qubits*) Reasons why errors often arise with qubits - and approaches to reducing these errors*) Different approaches to the hardware platforms of QC - and which are most likely to prove successful*) Ways in which academia can compete with (and complement) large technology companies*) The significance of "quantum supremacy" or "quantum advantage": what has been achieved already, and what might be achieved in the future*) The risks of a forthcoming "quantum computing winter", similar to the AI winters in which funding was reduced*) Other comparisons and connections between AI and QC*) The case for keeping an open mind, and for supporting diverse approaches, regarding QC platforms*) Assessing the threats posed by Shor's algorithm and fault-tolerant QC*) Why companies should already be considering changing the encryption systems that are intended to keep their data secure*) Advice on how companies can build and manage in-house "quantum teams"Music: Spike Protein, by Koi Discovery, available under CC0 1.0 Public Domain DeclarationSelected follow-up reading:https://en.wikipedia.org/wiki/Juan_Ignacio_Cirac_Sasturainhttps://en.wikipedia.org/wiki/Rydberg_atom