Femtosecond Laser Inscription of Integrated Diamond Quantum Photonics
Dr Vibhav Bharadwaj, Politecnico di Milano, Italy
Library, A.2.500, Staudtstr. 2
Apart from the outstanding perfect-for-application properties of diamond such as optical transparency, hardness, bio-inertness and thermal conductivity, it has enthralled the scientific community due to a naturally occurring imperfection, the Nitrogen Vacancy (NV) color center. The NV center has emerged as an encouraging candidate for quantum computing due to its long electron spin coherence times and its ability to be found, manipulated and read out optically. Additionally, the spin states are sensitive to magnetic and electric fields through the Zeeman and Stark effects, respectively and hence pose as a notable substrate for field sensing applications.
Recently, ultrafast laser writing (ULW) has emerged as a powerful tool for integrated photonics in diamond[2-4]. In this talk, the ability of ULW to inscribe optical waveguides, Bragg gratings, high aspect ratio microchannels and to deterministically inscribe NV centers in the bulk of diamond will be discussed. Integrated quantum photonic devices composing of laser inscribed waveguides coupled to laser written single NV centers in ultrapure CVD diamond samples, with the aim towards quantum information applications, have been achieved, as shown in Fig.1(a). For field sensing applications, ensemble NVs will be beneficial as they allow high sensitivities of detection. Laser writing of ensemble NVs in high nitrogen content diamond, grown through high-pressure-high-temperature (HPHT) technique have been performed. Optical waveguides have been written within the bulk of HPHT sample at a depth of ~20 μm, followed by inscription of static exposures all along the length of the waveguide, creating vacancies. High temperature annealing was performed on this waveguide-NV device to mobilize the vacancies generated by laser and to eventually to bind with a nitrogen atom in its vicinity and hence form an NV center. Confocal photoluminescence (PL) measurements performed on this waveguide-NV showed a bright fluorescence emission from within the waveguides, as shown in Fig.1(b). The waveguide inscription itself produced high density of NVs which was clearly visible when launching a 532 nm laser light into the waveguide and observing the streak of light after filtering the excitation wavelength, as shown in Fig.1(c). The NV density was estimated to be about 1.1×1015 based on the power dependence of PL saturation suggesting the possibility of a device with state-of-the-art magnetic and electric field sensitivities. We will discuss ways to further improve these sensitivities and integrate with other laser written elements for fully integrated lab on chip devices.
Vibhav Bharadwaj received his Bachelor of Science and Master of Science with specialization in photonics from Sri Sathya Sai Institute of Higher Learning, Puttaparthi, India. He obtained his PhD degree at Politecnico di Milano, Italy in the year 2018 with the thesis titled “Femtosecond laser microfabrication of 3D integrated photonic circuits in diamond for quantum information and magnetometry”. He is presently a Post-doctoral researcher at the Department of Physics, Politecnico di Milano and affiliated with Istituto di Fotonica e Nanotecnologie - Consiglio Nazionale delle Ricerche (IFN-CNR) working predominantly in laser inscription of color centers and single photon emitters in various materials for quantum sensing applications.