Protecting Quantum Computers From Crashing


A research group at RWTH Aachen University and Forschungszentrum Jülich has published research results on protecting quantum computers from qubit loss in the journal Nature



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The carriers of quantum information, so-called qubits, are susceptible to errors caused by undesired environmental interactions. These errors accumulate during a quantum computation. Correcting them is thus a key requirement for a reliable use of quantum information processors.

Qubits might also get lost from the quantum register altogether. Depending on the type of quantum computer, this may be due to the actual loss of particles, such as atoms or ions, or to the fact that quantum particles enter unwanted energy states and are no longer recognized as qubits. The information in the remaining qubits is then damaged and unprotected, which can lead to serious errors in the computation.

The Research Group for Theoretical Quantum Technology led by Professor Markus Müller from the Institute for Quantum Information at RWTH Aachen University and the Peter Grünberg Institute at Forschungszentrum Jülich, in collaboration with the Universities of Innsbruck and Bologna, has now developed methods that allow a trapped-ion quantum computer to adapt to the loss of qubits in real time and maintain the protection of the fragile quantum information. Professor Müller stresses that "combining quantum error correction with correction of qubit loss is a necessary next step towards large-scale and robust quantum computing." The results have now been published in the scientific journal Nature under the title Experimental Deterministic Correction of Qubit Loss.

The researchers developed two key techniques to protect their quantum computer from the loss of qubits. The first challenge was to detect the loss. Since directly measuring the qubit would destroy the information stored in it, the researchers developed a technique in which an additional ion was used to check whether the qubit in question was still present or not – without disturbing it.

The second challenge was to adapt the rest of the calculation in real time in case the qubit was indeed lost. According to Müller, this adaption was crucial in order to decode the quantum information afterwards and to protect the remaining qubits.

Full article: Experimental deterministic correction of qubit loss. Roman Stricker, Davide Vodola, Alexander Erhard, Lukas Postler, Michael Meth, Martin Ringbauer, Philipp Schindler, Thomas Monz, Markus Müller, Rainer Blatt. Nature 2020