. Scientific Frontline: More stable states for quantum computers

Tuesday, December 20, 2022

More stable states for quantum computers

The properties of gralmonium qubits are dominated by a tiny constriction of only 20 nanometers, which acts like a magnifying glass for microscopic material defects.
Illustration Credit: Dennis Rieger, KIT

Quantum computers are considered the computers of the future. A and O are quantum bits (qubits), the smallest computing unit of quantum computers. Since they not only have two states, but also states in between, qubits process more information in less time. Maintaining such a condition longer is difficult, however, and depends in particular on the material properties. A KIT research team has now produced qubits that are 100 times more sensitive to material defects - a crucial step to eradicate them. The team published the results in the journal Nature Materials.

Quantum computers can process large amounts of data faster because they perform many calculation steps in parallel. The information carrier of the quantum computer is the qubit. With qubits there is not only the information "0" and "1", but also values in between. The difficulty at the moment, however, is to produce qubits that are small enough and can be switched quickly enough to perform quantum calculations. Superconducting circuits are a promising option here. Superconductors are materials that have no electrical resistance at extremely low temperatures and therefore conduct electrical current without loss. This is crucial to maintain the quantum state of the qubits and to connect them efficiently.

Grailmonium qubits: superconducting and sensitive

KIT researchers have succeeded in developing novel and unconventional superconducting qubits. “The heart of a superconducting qubit is a so-called Josephson contact, which is used to store quantum information. This is exactly where we made a decisive change,” said Dr. Ioan M. Pop from the Institute for Quantum Materials and Technologies at KIT (IQMT). As a rule, such Josephson contacts are created for superconducting quantum bits by separating two aluminum layers by a thin oxide barrier. "In contrast, we only use a single layer of 'granular aluminum' for our qubits, a superconductor made of aluminum grains a few nanometers in size, which are embedded in an oxide matrix," says Pop. As a result, the material forms a three-dimensional network of Josephson contacts. “In the end, the entire properties of our qubit are dominated by a tiny constriction of only 20 nanometers. This makes it look like a magnifying glass for microscopic material defects in superconducting qubits and offers a promising perspective for their improvement,” adds Simon Günzler from IQMT

From a single cast: Qubits made entirely of granular aluminum

The qubits developed by the team are a fundamental further development of a previously tried-and-tested approach with so-called fluxonium qubits. In this previous version, parts made of granular aluminum and other parts were conventionally made from aluminum. In the current work, the researchers went the decisive step further and made the complete qubits out of granular aluminum. “As if you were simply cutting a quantum circuit out of a metal film. This opens up completely new possibilities for industrial production with etching processes and expanded areas of application for qubits, for example in strong magnetic fields,” says Dennis Rieger from the Physics Institute of KIT

The authors also protected this invention by a European patent.

Published in journalNature Materials

Source/CreditKarlsruhe Institute of Technology

Reference Number: qs122022_01

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