A German-Italian research team is investigating the influence of natural radioactivity on quantum bits. The question: Do superconducting circuits remain longer stable underground? They are looking for answers in the Gran Sasso rock massif.
Superconducting circuits are one of the leading technologies in developing quantum computers. Superconducting means that the circuits have lost their electrical resistance at low temperatures. Here, information is stored in superconducting qubits.
The qubit plays the same role for quantum computers as the bit does in classical computers. However, apart from the values zero and one, it can theoretically assume an infinite number of superposition states. One of the biggest research challenges is that superconducting qubits can only preserve their state for a very short time, as they are disturbed by various influences such as radioactivity.
A working group from the Karlsruhe Institute of Technology (KIT) and the Italian Istituto Nazionale di Fisica Nucleare (INFN) have now got to the bottom of the matter – in an underground laboratory in the Gran Sasso rock massif in the Apennines. In the Laboratori Nazionali del Gran Sasso, the researchers succeeded in protecting the building blocks of the qubits from the effects of natural radioactivity and thus significantly improving their stability.
»The underground facilities are located under 1,400 meters of rock, thus natural radioactivity from cosmic rays is reduced by a factor of one million,« explains Francesco Valenti, a PhD student in the research group of Ioan Pop at KIT. »Radioactivity induces simultaneous faults in circuits on the same chip. This is particularly harmful for quantum processors, because their error correction is based on the fact that if there is an error in one of the qubits, the others can still receive the information.«
INFN researcher Laura Cardani summarizes the results, saying, »Our study shows that a significant improvement can be achieved with operation in an environment with very low radioactivity.« Regarding next steps, Ioan Pop emphasizes that it is important to gain more understanding of the exact processes by which radioactivity degrades quantum circuits and to begin operating quantum processors underground.