Development of a quantum sensor using synthetic diamonds. Towards a wearable magnetoencephalograph

Abstract

A high-performance wearable sensor for measuring the electromagnetic activity generated by the human body could be very useful for certain fields of medicine, such as neurology or cardiology, by allowing its use in the natural environment of the subject. Furthermore, its applications outside of the medical field could also be impressive. Such a device does not currently exist since none of the technologies meets all the required characteristics. However, properly doped diamond crystals could offer us a new possibility. The physical properties of diamond crystals, such as color or electrical conductivity, can be controlled by impurities. In particular, when a diamond is doped with nitrogen and, under certain conditions, optically active nitrogenvacancy (NV ) centers can be induced. The center is a quantum spin system that enables, at room temperature, optical initialization and readout, and microwave coherent control, with applications in quantum information, quantum imaging and quantum sensing. Given the unprecedented multiple capabilities, brought together by these centers, in aspects such as their sensitivity, temporal and spatial resolution, miniaturization tolerance, operation in a wide range of temperatures, long spin coherence time, wide bandwidth and dynamic range, make it a perfect physical phenomenon for its application as a sensor. Specifically, and this is the main object of this doctoral thesis, as a sensor that allows wearable magnetoencephalography. In addition, the development of the material itself has been studied, creating color centers by ion irradiation and subsequent annealing from diamond samples. Irradiation causes damage to the crystalline structure of the diamond, generating vacancies, subsequent annealing allows its mobility so that, when combined with nitrogen atoms, they form nitrogen-vacancy couples that give the material the desired properties. This entire process has been studied in search of optimum the material. Finally, and to deepen the understanding of the properties of NV centers and how they are affected by their environment, like other centers or atoms in the lattice, the center has been studied using computational chemistry and its implementation using quantum computing