Technology Review
Computer scientists have built a superconducting number cruncher with a Von Neumann architecture that paves the way for a new era of quantum computation.

Back in 1946, the world’s first general purpose electronic computer was switched on at the University of Pennsylvania. The huge processing power of Electronic Numerical Integrator And Computer - ENIAC stunned the world, or at least the few dozen people who had any idea what it was for and why it was important.

But ENIAC had an important flaw. It could only be programmed by resetting a myriad switches and dials, a task that could take weeks. And this seriously hindered the computer’s flexibility.

The solution was not hard to find. it had already been outlined by Alan Turing, John Von Neumann and others: have a unit for number crunching and a separate electronic memory that could store instructions and data. That design meant that any reprogramming could be done relatively quickly, easily and electronically.

Today, almost all modern computers use this design, now known as the Von Neumann architecture.

The exception is the quantum computer. These devices use the strange properties of the quantum world to perform huge numbers of calculations in parallel. Consequently they have the potential to vastly outperform conventional number crunchers.

Unfortunately, physicists have only a vague and fleeting power over the quantum world and this means has prevented them the luxury of designing a Von Neumann-type quantum computer.

Until now. Today, Matteo Mariantoni at the University of California Santa Barbara and pals reveal the first quantum computer with an information processing unit and a separate random access memory.

Their machine is a superconducting device that stores quantum bits or qubits as counter-rotating currents in a circuit - this allows the qubit to be both a 0 and 1 at the same time. These qubits are manipulated using superconducting quantum logic gates, transferred using a quantum bus and stored in separate microwave resonators.

Let’s say upfront that the result is not a particularly powerful computer. Mariantoni and co show off their device by demonstrating a couple of simple but unspectacular algorithms but ones that were carefully chosen as the building blocks of more impressive tasks such as error correction and factoring large numbers.

Not that they’ve actually done any of those things. What’s impressive, however, is that they soon could since this approach is eminently scalable. “Our results provide optimism for the near-term implementation of a larger-scale quantum processor based on superconducting circuits,” say Mariantoni and co.

There has been no shortage of false dawns for quantum computing in the last 20 years or so. But it could that the Sun is about to rise on a new era of computation. If it does, everything that has gone before will one day seem as primitive as ENIAC seems to us.