Ph.D Thesis

Ph.D StudentAlfasi Nir
SubjectColor Defects in Diamond for Sensing Applications at
Low Temperatures
DepartmentDepartment of Electrical and Computer Engineering
Supervisor ASSOCIATE PROF. Eyal Buks


Hybrid quantum systems are being vastly explored as platforms for creating, storing, and transporting quantum information. One notable system is that combining a superconducting circuit and a solid-state spin system. In this thesis, we focus on a spin system composed of an ensemble of nitrogen-vacancy (NV) defects in diamond. Thanks to its long coherence time that can reach seconds at low temperatures and relatively easy initialization through optically induced spin polarization (OISP), the

NV center in diamond is among the most extensively studied spin systems today. In

addition, the NV center may be used as an excellent sensor for various applications,

including magnetometry where it can reach sensitivity on the order of pT/(Hz)1/2.

In this work, we use a large ensemble of NV centers at low temperatures and exploit its unique properties for various applications. In the first part, we employ diamond-based vectorial magnetometry for imaging the penetration of an externally applied magnetic field into a thin niobium film. The technique of diamond magnetometry is based on optical detection of magnetic resonance (ODMR) of negatively charged nitrogen-vacancy (NV-) defects inside a single crystal diamond. Our prototype diamond magnetometer is designed to allow magnetic imaging of an electrically wired sample at cryogenic temperatures through a coherent fiber bundle with 30,000 cores, using a complementary metal-oxide semiconductor (CMOS) camera. The current distribution of type-II superconducting thin film under perpendicular magnetic field is theoretically evaluated by employing the critical state model, where comparison between the experimental findings and theoretical predictions yields good agreement.

In the second part of this work, we explore the nonlinear regime of light-matter interaction in diamond using a superconducting spiral-shaped resonator coupled to a large ensemble of NV-centers. We introduce the method of cavity-based detection of magnetic resonance (CDMR) to detect resonance transitions of both NV- and nitrogen-14 substitution (P1) defects in a diamond wafer. We observe nonlinearity in cavity response and find that the coupling between the spins and superconducting microwave cavity imposes an upper bound upon the input microwave power for which the response remains linear. This upper bound has important implications for the sensitivity of traditional spin-detection protocols that are based on linear response. The experimental results are compared to theoretical predictions and excellent agreement is obtained in a wide range of externally controlled parameters.

In the last part of this work, we use ODMR and CDMR to detect and explore other paramagnetic defects in diamond, such as P1 defects. Our method does not require overlap between the resonances of the defects and is therefore applicable in a wide range of magnetic fields and frequencies and is verified by excellent fit to theoretical predictions. In addition, we explore the prospects of employing OISP for the generation of population inversion, which in turn may allow the construction of a diamond-based maser.