Highly Localized Delivery of Microwaves to Quantum Bits with a Scanning Loop Micro-Antenna

We demonstrate highly localized delivery of microwaves to quantum bits with a scanning loop micro-antenna. The quantum state of the qubits (ensembles of nitrogen vacancy centers in microdiamond) is read out optically, via optically detected magnetic resonance (ODMR). A 600 × 600 µm² via-based PCB loop antenna is specifically designed as efficient microwave excitation source. A piezo micromanipulator from Sensapex provides precise control of the antenna position above microdiamond containing nitrogen-vacancy (NV) centers, enabling spatially resolved ODMR measurements. 1D line and 2D imaging scans reveal the local microwave near-field distribution generated by the loop antenna. These results demonstrate spatially resolved ODMR mapping using a custom-built free-space optical configuration and establish a basis for future NV-based quantum sensing and microwave field characterization, as well as laying the foundation for quantum state manipulation of individual qubits using programmable, highly localized delivery of microwaves.