The spin of an electron or a nucleus in a semiconductor [1] naturally implements the unit of quantum information -the qubit -while providing a technological link to the established electronics industry [2]. The solid-state environment, however, may provide deleterious interactions between the qubit and the nuclear spins of surrounding atoms [3], or charge and spin fluctuators in defects, oxides and interfaces [4]. For group IV materials such as silicon, enrichment of the spinzero 28 Si isotope drastically reduces spin-bath decoherence [5]. Experiments on bulk spin ensembles in 28 Si crystals have indeed demonstrated extraordinary coherence times [6][7][8]. However, it remained unclear whether these would persist at the single-spin level, in gated nanostructures near amorphous interfaces. Here we present the coherent operation of individual 31 P electron and nuclear spin qubits in a top-gated nanostructure, fabricated on an isotopically engineered 28 Si substrate. We report new benchmarks for coherence time (> 30 seconds) and control fidelity (> 99.99%) of any single qubit in solid state, and perform a detailed noise spectroscopy [9] to demonstrate that -contrary to widespread belief -the coherence is not limited by the proximity to an interface. Our results represent a fundamental advance in control and understanding of spin qubits in nanostructures.It is well known that the Si/SiO 2 interface hosts a variety of defects that act as charge and spin fluctuators. Spin resonance experiments have documented the deleterious effects of the Si/SiO 2 interface on the coherence of donors in 28 Si, implanted at different depths [10]. Theoretical models suggest that magnetic fluctuation from paramagnetic spins at the interface cause the decohering noise [4], and recent work advocates the use of 'clock transitions' in 209 Bi donors [11] to obtain a spin qubit that is to first-order insensitive to magnetic noise. Fluctuations of interface charges or gate voltages can also cause decoherence, if there is a physical mechanism for electric fields to couple to the spin qubit states. Evidence of such effects was found for instance in carbon nanotube valley-spin qubits [12]. For donors in silicon, fluctuating electric fields can couple to the spin states by modulating the hyperfine coupling [13, 14] or the g-factor [15]. Here we operate single-atom spin qubits in isotopically purified 28 Si, with a residual 29 Si concentration of 800 ppm. Minimizing the effect 29 Si nuclear spin fluctuations allowed us not only to set new benchmarks for qubit performance in solid state, but also to uncover the microscopic origin of residual decoherence mechanisms, specific to a gated nanostructure.A substitutional P atom in Si behaves to a good approximation like hydrogen in vacuum, with energy levels renormalized by the effective mass and the dielectric constant of the host material [16]. Both the bound electron (e − ) and the nucleus ( 31 P) possess a spin 1/2 and constitute natural qubits with simple spin up/down eigenstates, which we denote ...

Electrically driven single-photon emitting devices have immediate applications in quantum cryptography, quantum computation and single-photon metrology. Mature device fabrication protocols and the recent observations of single defect systems with quantum functionalities make silicon carbide an ideal material to build such devices. Here, we demonstrate the fabrication of bright single-photon emitting diodes. The electrically driven emitters display fully polarized output, superior photon statistics (with a count rate of 4300 kHz) and stability in both continuous and pulsed modes, all at room temperature. The atomic origin of the single-photon source is proposed. These results provide a foundation for the large scale integration of single-photon sources into a broad range of applications, such as quantum cryptography or linear optics quantum computing.

This paper summarizes key findings in single-photon generation from deep level defects in silicon carbide (SiC) and highlights the significance of these individually addressable centers for emerging quantum applications. Single photon emission from various defect centers in both bulk and nanostructured SiC are discussed as well as their formation and possible integration into optical and electrical devices. The related measurement protocols, the building blocks of quantum communication and computation network architectures in solid state systems, are also summarized. This includes experimental methodologies developed for spin control of different paramagnetic defects, including the measurement of spin coherence times. Well established doping, and micro- and nanofabrication procedures for SiC may allow the quantum properties of paramagnetic defects to be electrically and mechanically controlled efficiently. The integration of single defects into SiC devices is crucial for applications in quantum technologies and we will review progress in this direction.

Control of individual spin qubits through local electric fields, suitable for large-scale silicon quantum computers.