Quantum and Integrated Photonics

Tin telluride (SnTe) is a topological crystalline insulator. Basically, this means that it hosts surface states that are topologically protected by the symmetries of the crystal. Earlier this year, we endeavored to study the quantum coherence of these surface states in nanowire loops made of this material. We did this by measuring oscillations in the conductance of these loops as a function of a perpendicular magnetic field (the Aharonov-Bohm effect).

Oscillations were observed, but they were periodic with the superconducting flux quantum (h/2e), not with the normal state flux quantum (h/e). Moreover, we observed a superconducting gap at low magnetic fields (< 150mT), low temperatures (< 350mK) and low applied currents (< 100nA).

Where did this superconducting behaviour come from? In this talk we will discuss the observed features, and we will take you with us on our recent journey of discovery to the source of the observed superconductivity.

Stimulated Brillouin scattering (SBS), a nonlinear optomechanical interaction involving light and GHz acoustic waves, has spurred groundbreaking applications from sub-Hertz level laser, ultra-high selectivity filter, to optical gyroscope. On-chip SBS has also been explored in low-loss and scalable silicon nitride platforms. Nevertheless, Brillouin gain coefficients in these platforms are limited to below 1 m⁻¹W⁻¹.

Very recently, theoretical works predict a strong SBS effect in thin-film lithium niobate (TFLN) waveguides. TFLN waveguides, recognized for their low loss, scalability, and versatility, have enabled unprecedented performances and functions in modulators, optical frequency combs, and quantum optics.

Here, we report, to the best of our knowledge, the first-ever experimental observation of backward SBS signals from TFLN waveguides. Notably, we observed the SBS effect in air-cladded z-cut TFLN waveguides with various crystal rotation angles (θ), confirming the crystal orientation dependence of the SBS strength. Furthermore, we experimentally demonstrated the enhancement of the SBS effect by surfaced acoustic waves by comparing x-cut TFLN waveguides with both silica and air cladding. The massive Brillouin gain coefficient (84.9 m−1W−1 in z-cut TFLN waveguides with θ=20°) in the mature TFLN platform makes it an ideal candidate for integrated Brillouin-based applications, including Brillouin-based microwave photonics filters and stimulated Brillouin lasers.

Aluminium nitride (AlN) exhibits high electro-optic, non-linear and piezo-electric coefficients and a large bandgap (i.e., 6.2 eV), which makes it an interesting material for photonic integrated circuits (PICs) with operation from ultraviolet to infrared wavelength range. In this work, AlN films deposited by reactive RF sputter deposition and annealed at 600 °C in a nitrogen atmosphere are discussed. The slab propagation losses of the AlN film are as low as 0.84 dB/cm at 978 mn and the propagation losses vary from 1.32 dB/cm to 8.33 dB/cm for wavelengths 785 and 451 nm. In the following, we investigate the capacity of this thin film to be used for integrated photonic circuits targeting 1550 nm wavelength, in which the slab propagation losses are expected to be even lower than the measured 0.84 dB/cm. The optical modes in 147 nm thick AlN ridge waveguide have been simulated with Lumerical MODE. Based on these simulations, waveguides with a width of 1.4 µm are fabricated. Then, electron beam lithography(RAITH EBPG5150) was used to pattern the photoresist. Next, the waveguide was defined by Reactive ion-etching in BCl3/Ar chemistry(Oxford PlasmaPro 100 Cobra). The waveguide propagation losses of these waveguides are determined from a set of microring resonators with different coupling gaps that have been designed. In this work, Waveguide propagation losses down to 0.7 dB/cm at 1550 nm wavelength have been measured.

Modern quantum technologies rely heavily on the efficient detection of single photons, making the development of scalable and integrated single-photon detectors a crucial endeavor. Pixel Photonics introduces an innovative approach to scalable single-photon detection solutions through the use of waveguide-integrated superconducting nanowire single-photon detectors (WI-SNSPDs) combined with highly scalable photonic integrated circuits (PICs).

SNSPDs offer near unity efficiency for detecting photons across the visible to near-infrared spectrum, with impressive features such as up to GHz count rates, sub-Hz dark count rates, and tens of picosecond timing jitter. By integrating these detectors into a photonic integrated circuit (PIC), we achieve high scalability, reduced footprint, low-loss waveguiding, and the incorporation of integrated photonic functionalities. Our detectors are coupled to independent fiber channels on the same chip.

In addition, the use of cryogenically stable electronics and fiber packaging allows us to create plug-and-play detector modules that can be housed in compact and portable closed-cycle cryostats. These solutions can be easily integrated into both rack-mountable all-in-one configurations and desktop-sized configurations with an external compressor, making them easy to use and accessible for everyday applications in quantum technologies, microscopy and life sciences, and laser communications.