The carriers of quantum information, the qubits, are susceptible to errors caused by undesirable interactions with the environment. These errors accumulate during a quantum calculation. Their correction is a central requirement for the reliable use of quantum computers. Similar to conventional computers, quantum computers also require a functioning error correction.
Today's quantum computers can certainly handle a certain number of arithmetical errors, for example bit flip or phase flip errors. However, qubits from the quantum register can also be lost, and there has been no protection against the potentially serious arithmetical errors resulting from this until now. Depending on the type of quantum computer, qubit losses can be due to the actual loss of particles such as atoms or ions, or to the fact that quantum particles, for example, enter undesirable electronic states so that their state is no longer recognised.
The Research Group for Theoretical Quantum Technology led by Prof. Markus Müller from RWTH Aachen University and the Jülich Peter Grünberg Institute, in collaboration with experimental physicists around Rainer Blatt from the University of Innsbruck and Davide Vodola at the University of Bologna, has now developed and implemented methods to protect against the loss of qubits. The new technique enables an ion trap quantum computer to adapt in real time to the loss of qubits and to maintain the protection of the fragile quantum information.