About the project
Quantum technology (QT) promises massive impacts on fields ranging from communication and cryptography to sensing and computing. Point defects in semiconductors are among the promising platforms to deploy quantum technology and are the subject of an immense international research interest, offering a wafer platform suitable for scaling, miniaturization and room temperature operation. Essential to many point defect based QT components is the single photon emitter (SPE), and a deeper understanding of how an ideal SPE functions and interacts with its environment will have a profound impact. The QuTe project explores several underdeveloped topics of point defects in silicon (Si) and silicon carbide (SiC) for QT applications, and involves identification of new SPEs, charge state identification and control, and manipulation and tuning of the emission wavelength, as well as theoretical modeling.
Objectives
The overarching research questions in the QuTe project are:
- What are the origins of the single photon emission signatures observed in Si and SiC, and in what charge state do they act as SPE?
- How can SPEs be manipulated to tune the emission wavelength, e.g. to obtain indistinguishable photons ?
- Can we employ quantum chemical calculations to reveal more information about the absorption and emission from SPEs, including time dependent information?
Background
The quantum compatible point defects in semiconductors combine all the necessary ingredients for facilitating quantum technology devices such as quantum computers and networks: (i) qubits based on either photon polarization or electron spin, (ii) gate operations applied to isolated spin systems, and (iii) SPEs for quantum state read-out and secure information transfer over large distances and within quantum computer systems. Importantly, in quantum technology based on point defects the device concepts and fabrication procedures are very similar to those used in the conventional semiconductor industry. Thus, the field is booming, featured by a race to discover and characterize new quantum compatible defect systems, and develop them towards devices.
Si based quantum technology has been of immense interest for some time. However, the SPEs from defects in Si were isolated only very recently. In particular, the G-center in Si, comprising an interstitial silicon atom bridging two adjacent carbon atoms residing at the Si sites [ 1 ], and formed after C+ ion implantations. Even though the G-center was known as an emitter in telecom wavelength from ensemble measurements [ 2 ], the evidence of the G-center isolation was optimistically received by the community. Starting from this important discovery, QuTe will follow several pathways for further tests and potential exploitations of the G-center and other defects in Si as qubits.
Meanwhile, SPEs in SiC have received massive attention. SiC has a wide band gap and low spin-orbit coupling, marking it as a suitable quantum material platform. Importantly, the carbon antisite – carbon vacancy pair (CAV silicon vacancy (V_Si), divacancy (VV) and the nitrogen-vacancy center (NV) defects in SiC have all been identified as room temperature SPEs with coherent spin control being demonstrated. However, a low overall photon count rate plagues emission from several of the SPEs in SiC, including VSi, and optical signals from isolated defects are challenging to detect without resorting to nanofabricated waveguides or implementation into photonic crystal cavities. Moreover, only one charge state of each defect center typically exhibits the required properties, with the others remaining dark and without the option of optically controlling and reading out the spin state. Recently, electrical control over the VSi and VV charge states was detected optically by monitoring the PL emission intensity from defects situated within the intrinsic region of 4H-SiC p-i-n diodes SiC, and we demonstrated the use of Schottky barrier diodes (SBDs) for charge state control of VSi [ 3 ]. Indeed, the SBD approach offers high switching frequencies and a simplified fabrication. Moreover, the electrical approach enables not only control of the intensity, but also the SPE energy, by employing the Stark effect. Identification, optical enhancement and charge state control will be key ingredients in the QuTe project.
The field of defect qubits is rapidly developing, and even though some methods for SPE control have been proposed, there is an urgent need for identification of unknown quantum defects and a better understanding and controlled manipulation of the SPEs. For successful integration of known SPEs one should seek (i) deliberate generation and positioning of a selection of point defect candidates, (ii) controlled switching and on-demand emission, (iii) control and tuning possibilities of emission wavelength, (iv) directionality, and (v) connectivity. In addition, new SPE candidates must be identified and explored combined with development of a theoretical framework that can model electrical and optical properties as well as time evolution and quantum mechanical entities. Moreover, there is a severe knowledge gap related to the modeling and understanding of time dependent effects such as spin coherence times and ultimately entanglement for qubit gate fabrication in semiconductor systems. The QuTe project intends on exploring several of the abovementioned avenues.
Infrastucture
The project uses the national infrastructure NorFab – The Norwegian Micro- and Nanofabrication Facility at the Micro- and Nanotechnology Lab (MiNaLab).
