MECHanical QUBIT With Enhanced Coherence

Condensed-matter qubits, such as transmons and spin qubits, benefit from compatibility with silicon-based fabrication, offering a path toward scalable quantum processors that could eventually host millions of qubits. However, despite their scalability, these platforms remain fundamentally limited in coherence, with typical quantum coherence times in the range of 0.01 to 1ms. Here we propose a radically new qubit architecture that encodes quantum information in mechanical vibrations, targeting quantum coherence times in the 1–100ms range. This mechanical qubit is realized by coupling a high-frequency mechanical oscillator to an electron double quantum dot (DQD) qubit. The key to surpassing the coherence of conventional electronic qubits lies in operating within the ultrastrong coupling regime, where the interaction strength between the mechanical and electronic degrees of freedom becomes comparable to the mechanical frequency. In this regime, mechanical nonlinearities at the quantum level emerge, enabling the definition of robust two-level systems with enhanced coherence. The project will demonstrate the mechanical qubit concept using suspended graphene drums integrated with bilayer graphene DQDs and superconducting resonators for readout. These components will be fabricated using all-2D-material van der Waals heterostructures to suppress charge noise and maximize coherence. A tight feedback loop between theory, fabrication, and experiment will guide optimization, enabling systematic identification and mitigation of decoherence sources. As proof-of-concept, we aim to realize coherent control of the mechanical qubit, a two-qubit gate, and force quantum sensing protocols with unprecedented sensitivity. This novel qubit platform opens the path to scalable quantum computing with improved quantum coherence and integrated sensing functionality.