The energy states of electrons in an atom follow the laws of quantum mechanics: they are not continuously distributed but restricted to certain well-defined values – this is also called quantisation. Such quantised states are the basis for quantum bits (qubits), with which scientists want to build extremely powerful quantum computers. To that end, the atoms have to be cooled down and trapped in one place.
Strong trapping can be achieved by ionising the atoms, which means giving them an electric charge. However, a fundamental law of electromagnetism states that electric fields that are constant in time cannot trap a single charged particle. By adding an oscillating electromagnetic field, on the other hand, one obtains a stable ion trap, also known as a Paul trap.
In this way, it has been possible in recent years to build quantum computers with ion traps containing around 30 qubits. Much larger quantum computers, however, cannot straightforwardly be realised with this technique. The oscillating fields make it difficult to combine several such traps on a single chip, and using them heats up the trap – a more significant problem as systems get larger. Meanwhile transport of ions is restricted to pass along linear sections connected by crosses.
Ion trap with a magnetic field
A team of researchers at ETH Zurich led by Jonathan Home has now demonstrated that ion traps suitable for use in quantum computers can also be built using static magnetic fields instead of oscillating fields. In those static traps with an additional magnetic field, called Penning traps, both arbitrary transport and the necessary operations for the future super-computers were realized. The researchers recently published their results in the scientific journal Nature.
