Silica or Silica on Silicon is a established optical integration platform [1], while the integrated Laser-written circuits' technology [2] offers additionally high customizability, and flexibility for rapid prototyping. Such integrated circuits could provide certain advantages for the development of robust and customizable quantum computers, although a critical issue to their required scalability is the integration capability of multiple single photon sources. While the main class of single photon sources is based on quantum dots embedded in semiconductor nanowires (NWQD) [3] allowing their deterministic integration, such hybrid circuits have been demonstrated only in high refractive index platforms like silicon or silicon nitride, due the modal characteristics compatibility to NWQD. It was shown recently [1] the restricting limitations of coupling in silica waveguides due to the low refractive index contrast leading to coupling performance <5%. A new light coupling scheme [4] proposed here overcomes this limitation, providing means for light coupling >60%. The scheme is based on the incorporation of an optical microsphere between the nanowire and the waveguide, which can be properly optimized and arranged in terms of: size (d), refractive index (n), and the distance of the microsphere between the nanowire (L) and waveguide (D). Given a suitable optical arrangement, the illuminated by the NWQD microsphere produces a photonic nanojet which excites efficiently the guided eigenmodes of the input channel waveguide facilitating the light coupling by the nanowire. The feasibility of the proposed method (Fig. 1) is demonstrated by considering readily available Alumina or Barium Titanate microspheres with diameter range 4μm - 12μm, leading to coupling efficiencies higher than 60%. The method is adequately tolerant [5] in displacements, misalignments, and imperfections and is feasible, as we show here, by current state of the art techniques like Focussed Ion Beam (FIB) for enabling NWQD-microsphere-waveguide alignment. The proposed method could enable the on-chip integration of multiple single photon emitters' in silica, and is expected to have a high impact in scalable photonic integrated circuits for quantum computing or sensing applications.

Entangled photon pairs at telecom wavelengths are essential for quantum communication, distributed computing, and quantum-enhanced sensing. The telecom O-band offers low chromatic dispersion and fiber loss, which is ideal for long-distance networks. Site-controlled nanowire quantum dots have emerged as a promising platform for generating single and entangled photons, offering high extraction efficiency and scalability. However, their operation has largely been restricted to the visible and first near-infrared (NIR-I) windows. Here, we demonstrate a bright source of entangled photon pairs in the telecom O-band based on site-controlled nanowire quantum dots. We measure a fine-structure splitting of 4.6 μeV, confirming suitability for high-fidelity polarization entanglement. Quantum-state tomography of the biexciton-exciton cascade reveals a maximum fidelity of 85.8 ± 1.1% to the Φ⁺ Bell state and a maximum concurrence of 75.1 ± 2.1%. This work establishes nanowire quantum dots as viable entangled photon sources at telecom, advancing scalable quantum technologies for fiber-based networks.

We present the first experimental demonstration of Fourier state tomography of photonic polarization states. We measure entangled pairs from a quantum dot, achieving results comparable to projective tomography with fewer components, verifying the authenticity and scalability of Fourier tomography for characterizing quantum state.

Quantum state tomography is used in quantum communication, computing, and cryptography to characterize quantum states enabling assessment and control of quantum systems. Rapidly scaling quantum technologies require fast, accurate, and simple techniques, but current tomography methods are bulky, hard to scale, and slow. To overcome these limitations, we experimentally demonstrate Fourier tomography [1], of single-photon and entangled photon pairs generated by a quantum dot. As shown in Fig. 1(a) for two-photon tomography, the setup consists of a continuously rotating quarter waveplate, a fixed linear polarizer and a single photon detector per qubit. As the waveplates rotates with different speed, we record the coincidences rate between the two detectors. This signal can be expressed as a Fourier series whose coefficients can be related to the polarization state of light. Fig. 1(b) shows the simulated coincidence rate as the waveplate rotates for input Bell states |ϕ⁺〉 and |ϕ⁻〉. By capturing the coincidences variations as a Fourier series through a single rotating element and fixed polarizer, we simplify the tomography process, providing an accurate, and simple approach suitable for scalable quantum systems.

We have investigated the possibility of using polarized single-photons as information carriers in an optical fiber with the aim of achieving error-free information transmission despite photon loss. To this end, a series of experiments are performed over a 20 km metro quantum link, where we compared the performance of three different error correcting and error detecting codes, based on three mutually orthogonal states |H〉, |V〉 and |0, alluding to two linearly polarized single photon states and the vacuum state, respectively. The experiment is carried out using a quantum dot single-photon source with g(2)(0) = 0.0053 ± 0.001, whose emitted photons are modulated and time-binned into code blocks. A 32 × 32 pixel black and white image is transmitted, demonstrating that error-correction can reduce errors significantly in this channel. Our method draws strength from the fact that the photon loss channel is asymmetric, allowing for loss errors to be efficiently pinpointed.

We demonstrate a frequency modulated continuous-wave (FMCW) light detection and ranging (LIDAR) system utilizing a superconducting nanowire single-photon detector (SNSPD) to measure vibrational spectra using reflected signals at the single-photon level. By determining the time-variant Doppler shift of the reflected probe signal, this system successfully reconstructs various audio signals, including pure sinusoidal, multi-tonal, and musical signals, up to 200 Hz, limited by the laser frequency modulation rate and the Nyquist sampling theorem. Additionally, we employ scanning galvo mirrors to perform 3D measurements and map audio signals from different regions in the scanned field of view. The integration of an SNSPD provides significant advantages such as near-unity detection efficiency, low dark count rates, and picosecond timing jitter, enabling measurements of vibrational spectra with as few as 100 detected reflected photons per laser sweep.

Coherent control of single-photon sources is crucial for the advancement of many photonic quantum technologies. In this work, we demonstrate on-demand single-photon generation and coherent manipulation of excitons in InAsP/InP nanowire quantum dots (NW QDs) (Fig. 1 (a)) under resonant excitation. Nanowire quantum dots are promising candidates for hybrid photonic integration due to their deterministic growth[1], high extraction efficiency[2], and precise spatial positioning capabilities[3].

The mobility edge (ME) is a crucial concept in understanding localization physics, marking the critical transition between extended and localized states in the energy spectrum. Anderson localization scaling theory predicts the absence of ME in lower dimensional systems. Hence, the search for exact MEs, particularly for single particles in lower dimensions, has recently garnered significant interest in both theoretical and experimental studies, resulting in notable progress. However, several open questions remain, including the possibility of a single system exhibiting multiple MEs and the continual existence of extended states, even within the strong disorder domain. Here, we provide experimental evidence to address these questions by utilizing a quasiperiodic mosaic lattice with meticulously designed nanophotonic circuits. Our observations demonstrate the coexistence of both extended and localized states in lattices with broken duality symmetry and varying modulation periods. By single-site injection and scanning the disorder level, we could approximately probe the ME of the modulated lattice. These results corroborate recent theoretical predictions, introduce a new avenue for investigating ME physics, and offer inspiration for further exploration of ME physics in the quantum regime using hybrid integrated photonic devices.

Detecting nonclassical light is a central requirement for photonics-based quantum technologies. Unrivaled high efficiencies and low dark counts have positioned superconducting nanowire single-photon detectors (SNSPDs) as the leading detector technology for integrated photonic applications. However, a central challenge lies in their integration within photonic integrated circuits, regardless of material platform or surface topography. Here, we introduce a method based on transfer printing that overcomes these constraints and allows for the integration of SNSPDs onto arbitrary photonic substrates. With a kinetically controlled elastomer stamp, we transfer suspended SNSPDs onto commercially manufactured silicon and lithium niobate on insulator integrated photonic circuits. Focused ion beam metal deposition then wires the detectors to the circuits, thereby allowing us to monitor photon counts with >7% detection efficiencies. Our method eliminates detector integration bottlenecks and provides new venues for versatile, accessible, and scalable quantum information processors.

High-purity single photon emitter at 1550 nm has been demonstrated with InAs quantum dots embedded in InAlGaAs lattice-matched to InP. The lowest g²(0) ~ 0.009 has been achieved with μm-pillars on the as-grown sample.