Are you interested in the fascinating world of quantum computing? If so, you'll be thrilled to know about the latest breakthrough in the field of silicon carbide-based quantum applications. Silicon vacancies in silicon carbide (SiC) have recently been proposed as an excellent candidate for quantum applications, thanks to their coherently controllable and sufficiently long coherence time properties.

But that's not all - silicon carbide also boasts a mature fabrication technique, and companies like Cree and Nortel readily provide silicon carbide wafers for researchers like us. By using a few MeV energy neutrons, electrons, and protons beams, we can create vacancies in this wafer, which can be annealed to remove unwanted defects and increase the dephasing time of the vacancies.

Under the supervision of Professor Suter, we have made a novel setup to study and characterize these silicon vacancies. We have measured the decoherence times of different silicon vacancies present in the 6H-SiC polytype, and even modeled the optical spin initialization of spin-3/2 silicon-vacancy centers at room temperature. We have also studied the angular polarization dependencies of these vacancies' emissions and the low-temperature ODMR of these vacancies, which was published in the npj Quantum Information volume 8, Article number: 23 (2022).

Moreover, we've observed the RF multiphoton absorption by these silicon vacancies, and for the first time, recorded Rabi and FID using the two and three RF photons. This discovery has opened up new avenues for studying multiphoton absorption transition amplitudes that depend on the RF component parallel to the c-axis and on the phase of the RF photons. 

Recently, observed an ODMR contrast of up to 6% for shallow silicon vacancy in 4H-SiC - better than anything out there!

In conclusion, our research on silicon vacancies in silicon carbide is an exciting development in the field of quantum computing, with a myriad of applications that could revolutionize the industry. 

Identification of ODMR peaks of silicon vacancies centers in 6H-SiC

We individually select the zero-phonon lines of the different silicon vacancies at low temperatures and record the corresponding ODMR spectra. ODMR allows us to correlate optical and magnetic resonance spectra and thereby separate signals from V1 and V3. The results also explain the observed sign change of the ODMR signal as a function of temperature. Materials Research Express, Volume 10, Number 11 (2023))

Experimental characterization of spin-3/2 silicon vacancy centers in 6H-SiC

ROOM Temperature Optical spin initialization of silicon vacancy centers 

Ph.D. RESEARCH WORK

My thesis deals with the ``generation, estimation and preservation of novel quantum states of two and three qubits, on an NMR quantum information processor”. Using the maximum likelihood ansatz, we have developed a method for state estimation such that the reconstructed density matrix does not have negative eigenvalues and the errors are within the space of valid density operators. 

Due to interactions with the environment, unwanted changes occur in the system, leading to decoherence. Controlling decoherence is one of the biggest challenges to be overcome to build quantum computers. We have used several experimental strategies to decouple the quantum system from its environment. These strategies are based on how much we know about system-environment interaction and what states we want to preserve. We first considered a case where we were aware of the system state but have no knowledge about its interaction with the environment. We demonstrated the efficacy of the super-Zeno scheme to tackle decoherence in this case. Then we considered a situation where only the subspace is known to which the system state belongs. To address such a situation we used a nested Uhrig dynamical decoupling scheme. 

Next, we considered situations where we have knowledge of the state of the system as well as its interaction with the environment. In such situations, since the noise model is known, decoupling strategies can be explicitly designed to cancel this noise. Using these decoupling strategies, we can experimentally extend the lifetime of time invariant discord of two-qubit Bell-diagonal states. 

and are also able to preserve the entanglement of three NMR qubits, to a remarkable extent.