In crude terms, our digitally driven information society is based on a simple binary opposition: 0 or 1. But what happens when other alternatives exist alongside these polar opposites? Might this give rise to a whole raft of different states and enable us to process complex information much faster?
It is precisely the prospect of going beyond conventional methods of data processing that has inspired such high hopes in the field of quantum physics – not only on the part of scientists in basic and theoretical research, but also among the CEOs of major corporations. Were this vision to materialise, and computers behave in accordance with the laws of quantum mechanics, it would open the door to a whole new world of applications. For example, such a powerful system would be able to determine the mechanism of proteins at a radically faster rate than a conventional computer could ever hope to achieve. This, in turn, would massively accelerate the development of new medicines.
A rocky road
Given such prospects, it is little wonder that quantum physics should exercise a fascination far beyond its immediate circle. Yet the road that will take us to a quantum computer capable of answering everyday questions is a rocky one – and much longer than many are prepared to admit. “We’re talking about decades, not years, before we reach that point,” says Jonathan Home, Professor of Experimental Quantum Optics and Photonics at ETH Zurich. And Professor Home is one of those working in a field in which quantum research is relatively far along. He uses individual atoms as qubits. These are the basic units of information used by a quantum computer to perform calculations. Home uses beryllium and calcium atoms held in special electrical ion traps. These are then manipulated with a laser according to the laws of quantum mechanics. “Atoms are great systems for information processing because they can be isolated – and because, provided they remain isolated, they can store quantum information for a couple of seconds or even minutes,” he explains.
In order to be able to use this information, however, these fragile quantum objects have to be reconnected with the everyday physical world. During this step, even the slightest anomalies can corrupt the entire system. The question is, therefore, how to reduce this susceptibility to error and, at the same time, increase the number of qubits.
Simpler and more robust
An obvious approach is to equip the systems with a degree of redundancy, i.e. to link several physical qubits to a single logical qubit. But this has a major drawback. Although redundancy renders the system more stable, it also makes it exponentially more complex – and, in turn, much more susceptible to error.