Diamond is the host for more than 500 optically active defects. Some of them represent significant interest not only in jewelry but also in quantum technologies. For instance, nitrogen-vacancy center was extensively studied over the last two decades because of its potential applications in sensing and quantum information processing. However, the poor optical properties of this defect limit construction of the scalable quantum registers or quantum networks. Recently emerged new family of diamond defects based on group-IV elements demonstrate superior optical characteristics and keep a promise to become a new platform for the realization of quantum networks. In this talk, I will discuss optical and spin properties of the group-IV defects, show recent progress in fabrication, studies, and application. I will also outline our approach combining long-lasting memory with the nearly ideal optical interface.

We report an efficient way to generate both even and odd optical analogs of Schrӧdinger cat states (SCSs) which are a superposition of two coherent states with opposite amplitudes. The resources consumed are single mode squeezed vacuum (SMSV) state and single photons. SCSs are formed after superimposing the input states with the subsequent detection of the number of photons in the auxiliary mode. We report the generation of eve/odd SCSs of amplitude 4.2 with fidelity >0.99 and an acceptable for offline experiments success probability. There is a tendency towards an increase in the size of the SCSs more demonstrated with an increase in the number of extracted photons. Entanglement is a key resource for quantum information processing, and so algorithms to generate entangled states on various hardware platforms are in demand. Extending the method allows us to generate multipartite entangled states (GHZ, W, cluster states) with SCSs.

Ever since Antoni van Leeuwenhoek built his single-lens microscope in the late 1600s, optical microscopy has remained instrumental in many scientific disciplines. However, conventional optical imaging still suffers from many limitations. The confluence of advanced computational methods and the exponential growth of computing power helps to revolutionize far-field optical imaging by rethinking both the optical design and the post-processing. I will show how computational methods push the boundaries of optical microscopy and provide imaging beyond the Abbe and Nyquist limits simultaneously in a simple and compact optical setup.

Quantum interference is a powerful instrument in modern quantum optics that can be used for precise time and phase measurements, generating entanglement and testifying non-locality of entangled systems. Nonlinear interferometry provides a new insight into quantum interference. A non-linear (SU(1,1)) interferometer can be obtained from a conventional linear interferometer by replacing the beam splitters with nonlinear media. Such interferometers indicate stability to the external losses and, at the same time, show an improvement in the phase sensitivity compared to their linear counterparts. Nonlinear interferometers are useful tools for creating single-mode sources and providing spectral engineering of light with different intensity profiles and mode contents. The interaction of matter with quantum light generated in the parametric down-conversion process and nonlinear interferometers leads to new phenomena which cannot be explained by semiclassical approaches. This talk will highlight our recent advances in quantum multimode nonlinear interferometers, their integrated implementations, generation of bright squeezed states of light with strong correlations within nonlinear interferometers, as well as in the interaction of matter with specific quantum states of light and new phenomena arising within such interaction.

Recent advances in quantum computers and simulators are steadily leading us towards full-scale quantum computing devices. Due to the fact that debugging is necessary to create any computing device, quantum tomography (QT) is a critical milestone on this path. In practice, the choice between different QT methods faces the lack of comparison methodology. Modern research provides a wide range of QT methods, which differ in their application areas, as well as experimental and computational complexity. Testing such methods is also being made under different conditions, and various efficiency measures are being applied. Moreover, many methods have complex programming implementations; thus, comparison becomes extremely difficult. In this study, we have developed a general methodology for comparing quantum state tomography methods. The methodology is based on an estimate of the resources needed to achieve the required accuracy. We have developed a software library (in MATLAB and Python) that makes it easy to analyze any QT method implementation through a series of numerical experiments. The conditions for such a simulation are set by the number of tests corresponding to real physical experiments. As a validation of the proposed methodology and software, we analyzed and compared a set of QT methods. The analysis revealed some method-specific features and provided estimates of the relative efficiency of the methods.

In this talk I'll cover the first experimental demonstration of a holistic quantum-enabled communications scheme with the record energy efficiency using time-resolving quantum receivers. I'll also discuss single-shot confidences obtained for individual quantum measurements in the state identification problem.