Quantum engineering

Kerr combs represent an ideal test-bench system for fundamental physics, particularly for quantum optics. In fact, understanding Kerr comb generation is strikingly simple when one considers the photon picture and describes the process as a four-photon interaction, where two input photons interact coherently via the Kerr nonlinearity to yield two output photons with different frequencies. Without further analysis, this interpretation already suggests that purely quantum phenomena based on the nonclassical nature of light can eventually arise in Kerr combs. However, observation of quantum fluctuations require to limit the so-called “technical noise” (classical perturbations of all kinds: acoustic vibrations, electrical noise, thermal fluctuations, etc.) to its minimum. We are working on compact platforms that isolate the resonator from environmental fluctuations, and allow for the observation of quantum effects such as squeezing and twin-photon generation in a compact setting. We expect the finalized system to comply with industrial standards of robustness, while being competitive for microwave photonics applications related to ultra-stable microwave generation. On the other hand, we also expect this packaged resonator to be a compact generator of various quantum states of light at room temperature, and with high wall-plug efficiency.

Further reading:
– Chembo (2016a)

Entanglement, twin-photon generation and squeezing

Various kinds of quantum states can be generated with Kerr combs depending on the pump power. In the configuration whe-re the system is under threshold, the pump field is the unique oscillating mode inside the resonator, and it triggers the phenome-non of spontaneous four-wave mixing, for which two photons from the pump are symmetrically up- and down-converted in the Fourier domain. This phenomenon, also referred to as parametric fluorescence, can only be understood and analyzed from a fully quantum perspective as a consequence of the coupling between the field of the central (pumped) mode and the vacuum fluctuations of the various side modes. In the configuration where the system is pumped above threshold, the system is in the regime of stimulated four-wave mixing: it displays quantum correlations and multimode squeezed states of light. The main interest of using ultra-high Q crystalline WGM resonators in quantum engineering is that the efficiency scales as the second or third power of the Q factor, depending on the final observable. Therefore, the perpective to generates non-classically correlated photons at a very high rates becomes possible with a compact setting and (sub-)mW pump power. However, the challenges are still difficult from both the theoretical and experimental standpoints. As highlighted above, it is important to suppress as much as possible the so-called technical sources of noise at the experimental level, in order to monitor quantum fluctuations with a high signal-to-noise ratio. From the theoretical angle, our research focuses on the study of effect such as higher-order dispersion and experimental imperfections (such as unbalanced detection, parasitic nonlinearities, etc.) which have a significant impact in the system.

Further reading:
– Chembo (2016b)

Quantum communication networks

A current line of research in the lab is to investigate the preparation, propagation and detection of entangled photon states in real-world optical fiber networks. These quantum states are affected by various impairments at each of these three stages and the main goal of our research activity along these lines is to explore realistic strategies to mitigate these detrimental effects, using commercial off-the shelf components.

Further reading:
– Galmès et al. (2019)