A superconducting circuit for quantum computing. (Credit: M.S. Allman/NIST)
Today’s computers are called digital because they encode information as ones or zeros,which can be represented, processed and stored by transistors that are either in their on or off states. Quantum computing extends this on-off digital paradigm through a property called superposition. This is the ability of a quantum object to be in multiple states – on, off, and something in between – all at the same time. This enables quantum computers to race through certain tasks, like factoring enormous numbers or calculating the results of very complex mathematical simulations, much, much faster than even the most powerful conventional supercomputers. This has unsettling consequences for internet security, since the codes used for passwords and data transferred are based on multiplying very large numbers to create numbers too large factor. Quantum computers could factor them within fractions of a second, making all security on the Internet obsolete. Fortunately, another quantum property, entanglement, could provide the solution. Once subatomic particles are entangled, or linked to one another, changing one will instantaneously change the other, even when they are separated. Entangled particles could be used to create security codes that only the owners of those particles could read.
The race to build the world’s first quantum computer is heating up. A string of new investments from tech industry heavyweights like Microsoft, Intel and Google could finally create a winner. We asked three physicists—Lieven Vandersypen, Shohini Ghose and John Martinis—to estimate the odds.
On November 5, Ronald Hanson and Renato Renner discussed the strongest proof yet that quantum theory, with faster-than-light links between entangled particles, explains the true nature of our universe. This is the transcript of their conversation.