Peter Byrne in Scientific American:
For more than 20 years, Ivan Deutsch has struggled to design the guts of a working quantum computer. He has not been alone. The quest to harness the computational might of quantum weirdness continues to occupy thousands of researchers around the world. Why hasn’t there been more to show for their work? As physicists have known since quantum computing’s beginnings, the same characteristics that make quantum computing exponentially powerful also make it devilishly difficult to control. The quantum computing “nightmare” has always been that a quantum computer’s advantages in speed would be wiped out by the machine’s complexity.
Yet progress is arriving on two main fronts. First, researchers are developing unique quantum error-correction techniques that will help keep quantum processors up and running for the time needed to complete a calculation. Second, physicists are working with so-called analog quantum simulators—machines that can’t act like a general-purpose computer, but rather are designed to explore specific problems in quantum physics. A classical computer would have to run for thousands of years to compute the quantum equations of motion for just 100 atoms. A quantum simulator could do it in less than a second.
Quanta magazine spoke with Deutsch about recent progress in the field, his hopes for the near future, and his own work on scaling up binary quantum bits into base-16 digits.
QUANTA MAGAZINE: Why would a universal quantum machine be so uniquely powerful?
IVAN DEUTSCH: In a classical computer, information is stored in retrievable bits binary coded as 0 or 1. But in a quantum computer, elementary particles inhabit a probabilistic limbo called superposition where a “qubit” can be coded as 0 and 1.
Here is the magic: Each qubit can be entangled with the other qubits in the machine. The intertwining of quantum “states” exponentially increases the number of 0s and 1s that can be simultaneously processed by an array of qubits. Machines that can harness the power of quantum logic can deal with exponentially greater levels of complexity than the most powerful classical computer. Problems that would take a state-of-the-art classical computer the age of our universe to solve, can, in theory, be solved by a universal quantum computer in hours.