Artist impression of a single-molecule transistor, where a molecule is connected to the source and the drain electrodes. The red lines illustrated the electric field caused by the gate electrode, located below.

The use of two-dimensional materials as building blocks in the production of p–n junctions has opened the door to novel device architectures with exceptional optoelectronics properties.

Superconducting quantum interference devices, or SQUIDs as they are better known, are capable of detecting minute variations in magnetic field. Embedding a suspended beam into the structure of d.c. SQUID enables this sensitivity to be exploited for measuring displacements. Superconducting quantum interference devices (SQUIDs) are the most sensitive detectors of magnetic flux1 and are also used as quantum two-level systems (qubits)2. Recent proposals have explored a novel class of devices that incorporate micromechanical resonators into SQUIDs to achieve controlled entanglement of the resonator ground state and a qubit3 as well as permitting cooling and squeezing of the resonator modes and enabling quantum-limited position detection4,5,6,7,8,9,10. In spite of these intriguing possibilities, no experimental realization of an on-chip, coupled mechanical-resonator–SQUID system has yet been achieved. Here, we demonstrate sensitive detection of the position of a 2 MHz flexural resonator that is embedded into the loop of a d.c. SQUID. We measure the resonator’s thermal motion at millikelvin temperatures, achieving an amplifier-limited displacement sensitivity of 10 fm Hz−1/2 and a position resolution that is 36 times the quantum limit.