QuPhon · Generation of Quantum multi-Phonon states in a mechanical oscillator

Generation of Quantum multi-Phonon states in a mechanical oscillator

Superconducting-qubit systems play a crucial role in modern quantum science and technology, serving as a highly promising platform for large-scale quantum processors. The QuPhon project proposed an innovative approach by using a megahertz-frequency mechanical oscillator as a long-lived quantum memory to support superconducting quantum computing. Despite advanced quantum control of mechanical oscillators based on cavity optomechanics in the microwave domain, integrating circuit optomechanical devices into large-scale superconducting-qubit systems has proven challenging due to the extremely small optomechanical coupling and the poor scalability of such optomechanical systems. The QuPhon project uses a quantum link based on itinerant microwave photons to combine a low-frequency mechanical oscillator with a superconducting qubit. Unlike all-in-one hybrid quantum systems, this approach maximizes the advantages of circuit optomechanics and superconducting qubits by establishing a quantum link between separate modules, avoiding unwanted side effects. In addition to the main goal of the QuPhon project, several important milestones in superconducting cavity optomechanics and superconducting qubits have been achieved. The project demonstrated multi-mode superconducting circuit optomechanical lattices in non-trivial topological phases, expanding the possibilities for studying many-body physics based on such an optomechanical platform. It also demonstrated the ability to track the thermalization of a quantum-squeezed mechanical state. This demonstrates that our mechanical oscillator possesses an ultra-coherence, providing an experimental platform for studying macroscopic quantum phenomena and quantum gravity. Moreover, these demonstrations based on circuit optomechanics confirmed that our revolutionary mechanical oscillators are useful for scalable and long-lived quantum memories for quantum computing and communication in modern science and technology. The project also established superconducting qubits for the first time at EPFL (École Polytechnique Fédérale de Lausanne), enhancing the institute's research capabilities. It has realized ultra-coherent superconducting qubits with lifetimes exceeding 0.4 milliseconds, which are among the best lifetimes in the field. With the exceptionally long qubit lifetimes, the project has discovered a new qubit loss mechanism for causing correlated errors induced by mechanical shocks, suggesting future mitigation strategies for scalable superconducting quantum computing.

Data: CORDIS, © European Union