At present, two experimental approaches for the realization of qubits are considered to be the most advanced: superconducting circuits and trapped ions. The former store quantum information in electronic components, the latter at different energy levels of individual atoms. In superconducting circuits, it was recently shown experimentally for the first time that quantum computers can perform highly specialized tasks that classical computers fail to do. The ion-based method, on the other hand, is characterized by the fact that the error rate of computing operations has always been much lower than with any other approach.
The ion method now developed by scientists from the University of Hannvover and the German national metrology agency PTB further reduces the error rate and thus delivers reliable calculation results much faster. It follows an approach in which the ions are held in a vacuum above a chip structure by means of electric fields.
The computing operations on the qubits are performed by sending microwave signals through special conductor loops embedded in the chip structure. Usually, extremely precisely controlled laser beams are used to perform computing operations. The use of microwaves has the advantage that microwave technology is very advanced and in widespread use which makes it relatively cheap to use. And that it is comparatively easy to control these fields.
The researchers have investigated how to perform the computing operations on the qubits most efficiently. This is a question that is also of great relevance in today's computer chips, because in the end the energy required per computing operation decides how many of them can be performed per second before the chip gets too hot. In the case of the ion-microwave quantum computer, the researchers were able to show that specially shaped microwave pulses, in which the microwave field is slowly built up and then broken down again, have error rates 100 times lower than a calculation operation in which the fields are simply switched on and off for the same energy input, despite the presence of interference sources.