Microwaves (MWs) are at the heart of many technologies,
e.g. for communication, timekeeping, remote sensing, and quantum information processing. Masers can boost faint MW signals quite nicely, but not under real-world conditions. The authors demonstrate efficient population inversion of optically pumped vacancy-related spins in SiC, at room temperature, and find realistic operating conditions for a SiC maser to serve as a continuous-wave amplifier. These spins can also be coherently coupled to superconducting cavities efficiently at cryogenic temperatures. These findings suggest this SiC system as a promising platform for MW photonics and quantum electronics.
Masers as telecommunication amplifiers have been known for decades, yet their application is strongly limited due to extreme operating conditions requiring vacuum techniques and cryogenic temperatures. Recently, a new generation of masers has been invented based on optically pumped spin states in pentacene and diamond. In this study, we pave the way for masers based on spin S = 3/2 silicon vacancy (VSi) defects in silicon carbide (SiC) to overcome the microwave generation threshold and discuss the advantages of this highly developed spin hosting material. To achieve population inversion, we optically pump the VSi into their mS = ±1/2 spin sub-states and additionally tune the Zeeman energy splitting by applying an external magnetic field. In this way, the prerequisites for stimulated emission by means of resonant microwaves in the 10 GHz range are fulfilled. On the way to realising a maser, we were able to systematically solve a series of subtasks that improved the underlying relevant physical parameters of the SiC samples. Among others, we investigated the pump efficiency as a function of the optical excitation wavelength and the angle between the magnetic field and the defect symmetry axis in order to boost the population inversion factor, a key figure of merit for the targeted microwave oscillator. Furthermore, we developed a high-Q sapphire microwave resonator (Q ≈ 104–105) with which we find superradiant stimulated microwave emission. In summary, SiC with optimized spin defect density and thus spin relaxation rates is well on its way of becoming a suitable maser gain material with wide-ranging applications.
The silicon vacancy center in Silicon Carbide (SiC) provides an optically addressable qubit at room temperature in its spin-
23 electronic state. However, optical spin initialization and readout are less efficient compared to those of spin-1 systems, such as nitrogen-vacancy centers in diamond, under non-resonant optical excitation. Spin-dependent fluorescence exhibits contrast only between
∣m=±3/2⟩ and
∣m=±1/2⟩ states, and optical pumping does not create a population difference between
∣+1/2⟩ and
∣−1/2⟩ states. Thus, operating one qubit (e.g.,
{∣+3/2⟩,∣+1/2⟩} states) leaves the population in the remaining state (
∣−1/2⟩ ) unaffected, contributing to background in optical readout. To mitigate this problem, we propose a sensing scheme based on duplex qubit operation in the quartet, using microwave pulses with two resonant frequencies to simultaneously operate
{∣+3/2⟩,∣+1/2⟩} and
{∣−1/2⟩,∣−3/2⟩} . Experimental results demonstrate that this approach doubles signal contrast in optical readout and improves sensitivity in AC magnetometry compared to simplex operation.
We report the realization of the optically induced inverse population of the ground-state spin sublevels of the silicon vacancies (V(Si)) in silicon carbide (SiC) at room temperature. The data show that the probed silicon vacancy spin ensemble can be prepared in a coherent superposition of the spin states. Rabi nutations persist for more than 80 μs. Two opposite schemes of the optical alignment of the populations between the ground-state spin sublevels of the silicon vacancy upon illumination with unpolarized light are realized in 4H- and 6H-SiC at room temperature. These altogether make the silicon vacancy in SiC a very favorable defect for spintronics, quantum information processing, and magnetometry.
We demonstrate high efficiency wavelength conversion via four wave mixing in amorphous silicon carbide ring resonators with a loaded quality factor of 70 000. Owing to the high quality factor and high nonlinearity of amorphous silicon carbide, −21 dB conversion efficiency is achieved with 15 mW pump power. Moreover, the thermo-optic coefficient (TOC) of amorphous silicon carbide is measured to be 1.4 × 10−4/°C at telecommunication wavelengths. Taking advantage of the high TOC, we demonstrate optical bistability in the silicon carbide ring resonator. This work presents amorphous silicon carbide as a promising platform for applications in optical signal processing.
Spin defects in wide band gap semiconductors are a leading contender in various areas of quantum technology. Most notably they have been established as a novel tool for nanoscale sensing and as major hardware for long distance quantum entanglement, necessary for quantum repeater structures [1],[2]. I will present the use of spin defects in Silicon Carbide (SiC) for quantum photonics and specifically for spin-photon interfaces [3]. Specifically, I will address the spin properties of the material and the interplay between photon emission and spin memory times. It turns out, that the silicon vacancy in SiC is an excellent compromise between photonic and spin quantum memory properties [4]. Even when incorporated into microscale photonic waveguides the optical transitions retain high quality such that long spin coherence times and almost transform-limited photon emission can be observed simultaneously.