Diamonds levitating in a Paul trap under vacuum: Measurements of laser-induced heating via NV center thermometry

We present measurements of the electronic spin resonance (ESR) of nitrogen vacancy (NV) centers in diamonds that are levitating in a ring Paul trap under vacuum. We observe ESR spectra of NV centers embedded in micron-sized diamonds at vacuum pressures of 2 × 10−1 mbar and the NV photoluminescence down to 10−2 mbar. Further, we use the ESR to measure the temperature of the levitating diamonds and show that the green laser induces heating of the diamond at these pressures. We finally discuss the steps required to control the NV spin under ultra-high vacuum.