Squeezing enhancement by suppression of noise through a resonant interferometric coupler.

We propose an integrated resonant structure to enhance squeezing by dual-pump spontaneous four-wave mixing (SFWM) while simultaneously suppressing parametric noise due to parasitic processes. The structure relies on a resonant interferometric coupler that allows one to engineer the field enhancement on-demand in the spectral region of interest. We analyze the different configurations in which the structure can operate, and we calculate the generated squeezing.

Broadband spontaneous parametric downconversion in reconfigurable poled linearly uncoupled resonators.

In this Letter, we theoretically study spontaneous parametric downconversion (SPDC) in a periodically poled structure composed of two linearly uncoupled resonators that are nonlinearly coupled via a Mach-Zehnder interferometer. The device does not require dispersion engineering to achieve efficient doubly resonant SPDC, and, unlike the case of a single resonator, one can reconfigure the system to generate photon pairs over a bandwidth of hundreds of nm. We consider the case of SPDC pumped at 775 nm in a periodically poled lithium niobate (PPLN) device compatible with up-to-date technological platforms.

Uncorrelated photon pair generation from an integrated silicon nitride resonator measured by time-resolved coincidence detection.

We measure the joint temporal intensity of signal and idler photon pairs generated by spontaneous four-wave mixing in a silicon nitride microresonator by time-resolved coincidence detection. This technique can be applied to any high-Q optical cavity whose photon lifetime exceeds the duration of the pump pulse. We tailor the temporal correlation of photon pairs by using a resonant interferometric coupler, a device that allows us to independently tune the quality factors of the pump and signal and idler resonances.

Polarization states and far-field optical properties in dielectric photonic crystal slabs.

We study the role of topological singularities like Bound States in a Continuum (BICs) or Circularly Polarized States (CPSs) in determining ellipticity of the far-field polarization in dielectric metasurfaces. Using finite-difference time-domain as well as rigorous coupled-wave analysis simulations, we determine the behavior of the Stokes parameter S in the whole k space above the light cone, with special regard to the region close to the singularities. Moreover, we clarify the relation between the topological singularities and the circular dichroism in reflectivity.

Silicon source of frequency-bin entangled photons.

We demonstrate an integrated source of frequency-entangled photon pairs on a silicon photonics chip. The emitter has a coincidence-to-accidental ratio exceeding 10. We prove entanglement by showing two-photon frequency interference with a visibility of 94.

A silicon source of frequency-bin entangled photons: publisher's note.

This publisher's note contains corrections to Opt. Lett.47, 6201 (2022)10.

Programmable frequency-bin quantum states in a nano-engineered silicon device.

Photonic qubits should be controllable on-chip and noise-tolerant when transmitted over optical networks for practical applications. Furthermore, qubit sources should be programmable and have high brightness to be useful for quantum algorithms and grant resilience to losses. However, widespread encoding schemes only combine at most two of these properties.

Generation of photon pairs by stimulated emission in ring resonators.

Third-order parametric downconversion (TOPDC) describes a class of nonlinear interactions in which a pump photon is converted into a photon triplet. This process can occur spontaneously or it can be stimulated by seeding fields. Here we show that stimulated TOPDC (StTOPDC) can be exploited for the generation of quantum correlated photon pairs.

Spontaneous parametric downconversion in linearly uncoupled resonators.

We study degenerate spontaneous parametric downconversion in a structure composed of two linearly uncoupled resonators, in which the linear properties of the fundamental and second-harmonic field can be engineered independently. As an example, we show that in this system it is simple to generate photon pairs that are nearly uncorrelated in energy. These results extend the use of linearly uncoupled resonators to the case of second-order nonlinear interactions.

Suppression of Parasitic Nonlinear Processes in Spontaneous Four-Wave Mixing with Linearly Uncoupled Resonators.

We report on a signal-to-noise ratio characterizing the generation of identical photon pairs of more than 4 orders of magnitude in a ring resonator system. Parasitic noise, associated with single-pump spontaneous four-wave mixing, is essentially eliminated by employing a novel system design involving two resonators that are linearly uncoupled but nonlinearly coupled. This opens the way to a new class of integrated devices exploiting the unique properties of identical photon pairs in the same optical mode.

Generation of hyper-entangled states in strongly coupled topological defects.

We investigate spontaneous parametric downconversion (SPDC) in a waveguide array supporting two strongly coupled topological guided modes. We show that it is possible to generate photon pairs that are hyper-entangled in energy and path. We study the state robustness against positional disorder of the waveguides, in terms of Schmidt number (SN), fidelity, and density matrix.

Squeezed light from a nanophotonic molecule.

Delicate engineering of integrated nonlinear structures is required for developing scalable sources of non-classical light to be deployed in quantum information processing systems. In this work, we demonstrate a photonic molecule composed of two coupled microring resonators on an integrated nanophotonic chip, designed to generate strongly squeezed light uncontaminated by noise from unwanted parasitic nonlinear processes. By tuning the photonic molecule to selectively couple and thus hybridize only the modes involved in the unwanted processes, suppression of parasitic parametric fluorescence is accomplished.

Light-activated shape morphing and light-tracking materials using biopolymer-based programmable photonic nanostructures.

Natural systems display sophisticated control of light-matter interactions at multiple length scales for light harvesting, manipulation, and management, through elaborate photonic architectures and responsive material formats. Here, we combine programmable photonic function with elastomeric material composites to generate optomechanical actuators that display controllable and tunable actuation as well as complex deformation in response to simple light illumination. The ability to topographically control photonic bandgaps allows programmable actuation of the elastomeric substrate in response to illumination.

Long-range Bloch surface waves in photonic crystal ridges.

We theoretically study light propagation in guided Bloch surface waves (BSWs) supported by photonic crystal ridges. We demonstrate that low propagation losses can be achieved just by a proper design of the multilayer to obtain photonic band gaps for both light polarizations. We present a design strategy based on a Fourier analysis that allows one to obtain intrinsic losses as low as 5 dB/km for a structure operating in the visible spectral range.

Electrically driven source of time-energy entangled photons based on a self-pumped silicon microring resonator.

Time-energy entangled photon pairs are fundamental resources for quantum communication protocols since they are robust against environmental fluctuations in optical fiber networks. Pair sources based on spontaneous four-wave mixing in silicon microring resonators usually employ expensive external tunable lasers to compensate for ambient fluctuations; adopting self-pumped configurations, instead, lifts the need for such external source. Here we demonstrate the emission of time-energy entangled photon pairs at telecom wavelengths from a silicon self-pumped ring, obtaining a Franson interference fringe with 93.

Spontaneous parametric down conversion in a doubly resonant one-dimensional photonic crystal.

We study spontaneous parametric down conversion (SPDC) in a one-dimensional photonic crystal designed to operate in a doubly resonant configuration, where the frequencies of the pump and the generated photons are both tuned to band-edge resonances. We investigate the spectral correlations of the generated photons as a function of the spectral width of the pump, and demonstrate that the SPDC generation rate can scale with the fifth power of the structure length in the limit of a quasi-continuous-wave pump. We show that such an unusual scaling can be simply connected with the scaling of second-harmonic generation in the same structure, illustrating the general link between spontaneous and stimulated parametric nonlinear processes.

Stimulated four-wave mixing in linearly uncoupled resonators.

We experimentally demonstrate stimulated four-wave mixing in two linearly uncoupled integrated $ {{\rm Si}_3}{{\rm N}_4} $SiN micro-resonators. In our structure, the resonance combs of each resonator can be tuned independently, with the energy transfer from one resonator to the other occurring in the presence of a nonlinear interaction. This method allows flexible and efficient on-chip control of the nonlinear interaction, and is readily applicable to other third-order nonlinear phenomena.

Bloch-surface-wave photonic crystal nanobeam cavity.

We theoretically demonstrate a nanobeam cavity based on a photonic crystal ridge that supports localized Bloch surface waves (BSWs) propagating at the truncation interface of a periodic multilayer. Combining the appealing characteristics of a nanobeam cavity (such as flexible geometry, small footprint size, and an etching-free fabrication with the leading lithographic technologies) with the versatility of BSW (whose dispersion relation is finely tunable as compared to other surface waves), this structure may prove to be a customizable visible-to-IR platform, well suited for a number of applications ranging from optical sensing to the control of single-photon emission from embedded nanoemitters such as quantum dots or color centers.

Three-Photon Discrete-Energy-Entangled W State in an Optical Fiber.

We experimentally demonstrate the generation of a three-photon discrete-energy-entangled W state using multiphoton-pair generation by spontaneous four-wave mixing in an optical fiber. We show that, by making use of prior information on the photon source, we can verify the state produced by this source without resorting to frequency conversion.

Strong Nonlinear Coupling in a Si_{3}N_{4} Ring Resonator.

We demonstrate that nondegenerate four-wave mixing in a Si_{3}N_{4} microring resonator can result in a nonlinear coupling rate between two optical fields exceeding their energy dissipation rate in the resonator, corresponding to strong nonlinear coupling. We demonstrate that this leads to a Rabi-like splitting, for which we provide a theoretical description in agreement with our experimental results. This yields new insight into the dynamics of nonlinear optical interactions in microresonators and access to novel phenomena.

Nonlinear Coupling of Linearly Uncoupled Resonators.

We demonstrate a system composed of two resonators that are coupled solely through a nonlinear interaction, and where the linear properties of each resonator can be controlled locally. We show that this class of dynamical systems has peculiar properties with important consequences for the study of classical and quantum nonlinear optical phenomena. As an example we discuss the case of dual-pump spontaneous four-wave mixing.

Stimulated emission tomography: beyond polarization.

In this work, we demonstrate the use of stimulated emission tomography to characterize a hyperentangled state generated by spontaneous parametric downconversion in a cw-pumped source. In particular, we consider the generation of hyperentangled states consisting of photon pairs entangled in polarization and path. These results extend the capability of stimulated emission tomography beyond the polarization degree of freedom and demonstrate the use of this technique to study states in higher dimension Hilbert spaces.

Biomaterial-Based "Structured Opals" with Programmable Combination of Diffractive Optical Elements and Photonic Bandgap Effects.

Naturally occurring iridescent systems produce brilliant color displays through multiscale, hierarchical assembly of structures that combine reflective, diffractive, diffusive, or absorbing domains. The fabrication of biopolymer-based, hierarchical 3D photonic crystals through the use of a topographical templating strategy that allows combined optical effects derived from the interplay of predesigned 2D and 3D geometries is reported here. This biomaterials-based approach generates 2D diffractive optics composed of 3D nanophotonic lattices that allow simultaneous control over the reflection (through the 3D photonic bandgap) and the transmission (through 2D diffractive structuring) of light with the additional utility of being constituted by a biocompatible, implantable, edible commodity textile material.

Integrated sources of photon quantum states based on nonlinear optics.

The ability to generate complex optical photon states involving entanglement between multiple optical modes is not only critical to advancing our understanding of quantum mechanics but will play a key role in generating many applications in quantum technologies. These include quantum communications, computation, imaging, microscopy and many other novel technologies that are constantly being proposed. However, approaches to generating parallel multiple, customisable bi- and multi-entangled quantum bits (qubits) on a chip are still in the early stages of development.