Single-gate, multipartite entanglement on a room-temperature quantum register

Experimental system

The sample used in this work is a type-IIa electronic-grade synthetic diamond (Element Six) with a natural abundance of ¹³C impurities. The NV centre is at the focus of a solid immersion lens encircled by an antenna for microwave (mw) frequency control. All experiments are performed at room temperature in ambient conditions. A permanent magnet was aligned to the NV symmetry axis using pulsed electron-spin resonance experiments and positioned to create a magnetic-field strength of 338 G. The magnetic-field strength was chosen to minimize nuclear-qubit gate durations and angular errors. Further details of the field alignment and simulations to determine the field strength are provided in Supplementary Section VII.

Green (532-nm) laser pulses of 2 μs were used to (re)initialize the electron spin and charge state through optical pumping, and shorter 300-ns pulses were used to measure the spin-state photoluminescence contrast. The synchronization of the optical and mw signals was achieved using two different configurations. The first used two arbitrary waveform generators, one (Tektronix AWG520) dedicated to optical control and the other (Tektronix AWG7102), for mw control. The second configuration used a Swabian Instruments PulseStreamer 8/2 for both optical and mw control. Additional details are provided in Supplementary Section I. Electron gate errors were quantified using bootstrap tomography of pulses⁵⁰ (Supplementary Section II).