Research News

Wed, 12/09/2020 | Implementation of Conditional Phase Gates Based on Tunable ZZ Interactions

Quantum computers, which have the capability to outperform classical computers on specific computational tasks, heavily rely on high-performance two-qubit gates for the realization of quantum algorithms.  In superconducting circuits, two-qubit gates are typically based on a transversal qubit-qubit coupling, implemented either by rf-control or the in-situ frequency tunability of computational qubits.

In this work, we demonstrate a novel approach using a tunable cross-Kerr-type ZZ interaction between two qubits which we realize with a flux-tunable coupler element.
This approach ensures direct control of the acquired conditional phase, without relying on excitation transfer or sideband transitions, and thus features an inherent resilience to leakage and cross talk, both major concerns in the light of recent progress towards full-scale quantum error correction. Additionally it innately enables the realization of continuous gate sets, highly beneficial for near-term variational quantum algorithms. A simple control paradigm and robust performance ensure easy scalability and high compatibility with existing platforms.

Fri, 11/13/2020 | Andreas Wallraff receives Helmholtz International Fellow Award 2020

Andreas Wallraff receives one of the 2020 Helmholtz International Fellow Awards of the Helmholtz Association of German Research Centres. The award serves also to expand an existing cooperation with scientists at the Forschungszentrum Jülich (Germany).

Tue, 10/20/2020 | A hardware-efficient gate set for superconducting qubits is shown to improve the performance of deep quantum optimization algorithms.

Quantum computers have the potential to solve problems that today’s computers cannot solve in a reasonable amount of time. However, their computations are not yet reliable, meaning that algorithms with many operations cannot be executed without significant errors. This article presents a method to reduce these errors by reducing the total number of operations required to execute a quantum optimization algorithm. This work thereby offers an approach to solving more complex problems on existing and near-term quantum computers.

The optimization algorithm considered in this work uses an Ising-type interaction between pairs of qubits. In prior work, this interaction was typically realized with a long sequence of standard quantum gates. By developing a gate that directly realizes the desired interaction, this work presents a hardware-efficient implementation that reduces the total number of gates executed on the quantum computer. This reduction in the number of gates results in a lower number of errors and, therefore, improves the overall performance of the algorithm.

The results demonstrate that using hardware-efficient gates is a key component in extending the impact of near-term quantum computers. In the future, the development of related types of hardware-efficient gates might enable quantum computers to tackle an even broader range of problems.

Thu, 03/05/2020 | 2020 virtual APS March Meeting

The 2020 APS March Meeting was cancelled due to health concerns relating to the spread of the coronavirus disease (COVID-19). The presentations of the Quantum Device Lab group members Simon Storz, Christian Kraglund Andresen, Ants Remm and Johannes Herrman were uploaded on the Virtual March Meeting platform.

Thu, 03/05/2020 | Longest microwave quantum link

In our lab, we have realized the first quantum coherent communication protocol operated between superconducting quantum circuits located in two cryogenic systems separated by a distance of 5 meters.