Digital and analogue work hand in glove
Jülich researchers are involved in the DAQC joint project. It aims to build and operate a digital-analogue quantum computer. Analogue quantum computers, in which the qubits interact continuously with each other, are less prone to error. However, they are not universally programmable. Their robustness is now to be combined with the flexible computing power of digital circuits.
Yin-yang qubits go perfectly well together
An international team involving Jülich researchers has succeeded in perfectly entangling two qubits. This entanglement is essential for the two information carriers to be able to interact with each other at all. In this, however, the qubits are typically always hindered by a parasitic interaction based on mutual repulsion. This leads to errors when calculating. The scientists have now coupled two complementary types of superconducting qubits: the two differed in the sign of what’s known as anharmonicity, through which the mutual repulsion could be avoided. As in the Far Eastern yin-yang symbol, the two opposing qualities balanced each other out. The researchers were able to show that the accuracy of the computing operation could be significantly improved for the tiny quantum circuit.
Ion traps and supercomputers calculate together
Forschungszentrum Jülich also contributes to the joint project IQuAn. It focuses on quantum computers that work with ions in traps. Their advantage: they retain their quantum state for a relatively long time. In the IQuAn project, novel architectures are being tested for such systems, which allow for up to 100 qubits to calculate together. A hybrid system is planned in which a quantum processor is connected to a high-performance computer.
Precise control improves qubit quality
The GeQCoS project has set itself the goal of fundamentally improving quantum processors with superconducting qubits. The central component is to consist of only a few computing cells, but they will be more strongly interconnected than in previous models. Particular emphasis is placed on improving the quality of the qubits. Among other things, Jülich researchers are contributing methods for the precise control of qubits to GeQCoS.
A gyrator ensures quantum balance
Researchers from Jülich, Aachen, Basel and Delft have designed a quantum circuit with a built-in passive error correction. It is based on qubits in superconducting loops. Usually, errors here have to be corrected by active intervention: several unstable qubits have to be combined to form a logical qubit. This makes it possible to identify errors and eliminate them through corrective operations. In the novel circuit, a so-called gyrator renders this intervention redundant. The electrical component has two ports and couples current at one port to voltage at the other. It is implemented between two superconducting qubit loops and stabilises the stored information. This principle could greatly simplify the construction of a quantum computer with a large number of qubits in the future.
Illustrations: Christian Marchionna