We present a system of four ring resonators capable of generating programmable polarization and frequency-bin entangled photon pairs on an integrated photonic device. Each ring is pumped with a continuous wave, generating photon pairs with the same polarization in two pairs of frequency bins via spontaneous fourwave mixing. We show that the density operator of the generated state represents a hyperentangled state in the polarization and frequency bin degrees of freedom. We also calculate the generation rate of the state.

We present an approach for designing sources of postselected multipartite states based on photon-pair sources. Our approach can be applied to arbitrary target states in different encoding schemes and physical platforms. It also allows one to limit the types of components to be used in the device, such that lossy or difficult-to-implement optical elements can be avoided. As an example, we apply this strategy to design a passive integrated source of frequency-bin-encoded high-dimensional GHZ states with a 10-kHz on-chip generation rate for picojoule pump pulses.

We present a method for describing nonlinear electromagnetic interactions in integrated photonic devices utilizing an asymptotic-in/out field formalism. Our method expands upon previous continuous wave asymptotic treatments by describing the evolution non-perturbatively for an arbitrary pulsed input. This is presented in the context of a squeezing interaction within an integrated microring resonator side coupled to an input/output waveguide, but is readily generalizable to other integrated structures, while including a variety of (non-squeezing) third-order interactions. An example of a single-pump, non-degenerate squeezing interaction is studied, which is shown to match well with standard coupled-mode treatments for high-finesse resonators, as well as previous perturbative treatments dealing with the generation of pairs with low probability.

We explore how III-V semiconductor microring resonators can efficiently generate photon pairs and squeezed vacuum states via spontaneous parametric down-conversion by utilizing their built-in quasi-phase-matching and modal dispersion. We present an analytic expression for the biphoton wave function of photon pairs generated by weak pump pulses and characterize the squeezed states that result under stronger pumping conditions. Our model includes loss and captures the statistics of the scattered photons. A detailed sample calculation shows that for low pump power conversion efficiencies of 10-5, corresponding to a rate of 39 MHz for a pump power of 1 mu W, are attainable for rudimentary structures such as a simple microring coupled to a waveguide, in both the continuous-wave and pulsed-excitation regimes. Our results suggest that high levels of squeezing and pump depletion are attainable, possibly leading to the deterministic generation of non-Gaussian states.

We derive the macroscopic charge and current densities of a Chern insulator initially occupying its electronic ground state as it responds to a finite-frequency electric field; we use a previously developed formalism based on microscopic polarization and magnetization fields in extended media. In a topologically trivial insulator, our result reduces to the familiar expression for the induced current density in linear response obtained from a Kubo analysis. However, for a Chern insulator, we find an extra "topological" term involving the (first) Chern number associated with the occupied bands, encoding the quantum anomalous Hall effect in the presence of a frequency- dependent electric field. While an analogous term has been introduced in the "modern theories of polarization and magnetization" for the linear response of finite-sized systems to static electric fields, our expression is valid for bulk Chern insulators in the presence of both static and finite-frequency electric fields, being derived analytically from a microscopic treatment of the electronic degrees of freedom, and can be generalized in a straightforward way to describe the response of a Chern insulator to electromagnetic fields that are not only frequency-dependent but also spatially inhomogeneous.

We introduce a novel method for modelling squeezed light generation in mi-croring systems beyond the perturbative regime, without necessitating a Lorentzian resonance structure. As such, this method is applicable within broad ranges of finesse.

We propose a source of visible entangled photon pairs encoded in multiple frequency bins of a ring resonator, with predicted generation rates of ~ 10MHz/(mW) 2 , offering potential applications in satellite QKD.

We calculate the fluorescence of cold cesium atoms excited by low intensity, non-degenerate squeezed light, which enhances the fluorescence rate compared to classical light. The signal is predicted to be in an experimentally detectable regime.

We present a multimode theory of squeezed state generation in resonant systems valid for arbitrary pump power and including pump depletion. The Hamiltonian is written in terms of asymptotic-in and -out fields from scattering theory, capable of describing a general interaction. As an example we consider the lossy generation of a highly squeezed state by an effective second-order interaction in a silicon nitride ring resonator point-coupled to a waveguide. We calculate the photon number, Schmidt number, and the second-order correlation function of the generated state in the waveguide. The treatment we present provides a path forward to study the deterministic generation of non-Gaussian states in resonant systems.

We experimentally study the tunability of second harmonic generation (SHG) from a two-dimensional (2D) material in a 2D material/dielectric film/substrate layered structure. Such tunability arises from two interferences: one is between the incident fundamental light and its reflected light, and the other is between the upward second harmonic (SH) light and the reflected downward SH light. When both interferences are constructive, the SHG is maximally enhanced; it becomes attenuated if either of them is destructive. The maximal signal can be obtained when both interferences are perfectly constructive, which can be realized by choosing a highly reflective substrate and an appropriate thickness for a dielectric film that has a large difference in its refractive indices at the fundamental and the SH wavelengths. Our experiments demonstrate variations of three orders of magnitude in the SHG signals from a monolayer MoS2/TiO2/Ag layered structure.

We present a strategy for designing passive sources of multipartite frequency-bin-encoded states, based on the target state’s graph representation. As examples we present integrated sources of three- and four-photon GHZ states, and four-photon L a 4 states.

We develop a formalism to describe squeezed light with large spectral-temporal correlations. This description is valid in all regimes, but is especially applicable in the long pulse to continuous-wave limit where the photon density at any particular time is small, although the total number of photons can be quite large. Our method relies on the Whittaker-Shannon interpolation formula applied to the joint temporal amplitude of squeezed light, which allows us to ``deconstruct'' the squeezed state. This provides a local description of the state and its photon statistics, making the underlying physics more transparent than does the use of the Schmidt decomposition. The formalism can easily be extended to more exotic nonclassical states where a Schmidt decomposition is not possible.

We calculate the rate of spontaneous parametric down-conversion, and generated biphoton wavefunction, in an AlGaAs microring resonator designed to take full advantage of the quasi-phase matching occurring as the light propagates around the ring.

We present a programmable integrated source of polarization and frequency-bin hyperentangled states with a predicted purity of 99.96% and a generation rate of ~ 1 × 10 5 Hz.

We demonstrate that genuine multipartite entangled states can be generated using frequency bin encoding in integrated photonic platforms. We introduce a source of four-photon GHZ states, and a source of three-photon W states. We predict generation rates on the order of 10$^4$ Hz for a silicon microring source with milliwatt pump powers. These results, along with the versatility and scalability of integrated structures, identify this as a promising approach for the generation of higher-dimensional and larger entangled states.

We calculate the two-photon absorption of squeezed light by rubidium atoms. In the region of large enhancement, Doppler broadening significantly decreases the effectiveness of photon correlations, leading to the prediction of unspectacular fluorescence counts.

For squeezed light with a large spectro-temporal correlation, we construct an approximate Schmidt decomposition, which is equivalent to the Whittaker-Shannon interpolation formula. Our decomposition leads to an intuitive description of the squeezed light photon statistics.

Several plasmonic nanoparticles supporting dipolar resonances can couple to form normal modes. Here, we develop an analytical model to explain the formation of nonradiative "dark" and radiative "bright" modes through radiative coupling in bilayers consisting of dipolar nanoantenna arrays that are separated by a subwavelength distance. We also include near-field contributions in our model and show that the absorption and reflectance spectra obtained from our model agree reasonably well with the respective finite-difference time-domain simu-lation results for both perfectly aligned and misaligned bilayers. The ability to vary the reflection and absorption spectra of these bilayers by changing the material and geometrical parameters has potential applications in the design of efficient spectral filters. We also show that we can selectively excite these modes by adjusting the phase between two counterpropagating normally incident fields, which has applications in all-optical modulators and switches based on purely linear interferometric effects.

The optical injection of charge and spin currents are investigated in Ge$_{1-x}$Sn$_{x}$ semiconductors as a function of Sn content. These emerging silicon-compatible materials enable the modulation of these processes across the entire mid-infrared range. Under the independent particle approximation, the one- and two-photon interband absorption processes are elucidated, and the evolution of the coherent control is discussed for three different polarization configurations. To evaluate the contribution of high-energy transitions, a full-zone 30-band k$\cdot$p is employed in the calculations. It was found that, besides the anticipated narrowing of the direct gap and the associated shift of the absorption to longer wavelengths, incorporating Sn in Ge also increases the one-photon degree of spin polarization (DSP) at the $E_1$ resonance. Moreover, as the Sn content increases, the magnitude of the response tensors near the band edge exhibits an exponential enhancement. This behavior can be attributed to the Sn incorporation-induced decrease in the carrier effective masses. This trend appears to hold also at the $E_1$ resonance for pure spin current injection, at least at low Sn compositions. The two-photon DSP at the band edge exceeds the value in Ge to reach 60 % at a Sn content above 14 %. These results demonstrate that Ge$_{1-x}$Sn$_{x}$ semiconductors can be exploited to achieve the quantum coherent manipulation in the molecular fingerprint region relevant to quantum sensing.

We present a detailed study of the generation of photon pairs by spontaneous four-wave mixing in a structure composed of two linearly uncoupled resonators, where energy can be transferred from one resonator to another only through a nonlinear interaction. Specifically, we consider the case of two racetrack-shaped resonators connected by a coupler designed to guarantee that the resonance comb of each resonator can be tuned independently and to allow the nonlinear interaction between modes that belong to different combs. We show that such a coupler can be realized in at least two ways: A directional coupler or a Mach-Zehnder interferometer. For these two scenarios, we derive analytic expressions for the pair-generation rate via single-pump spontaneous four-wave mixing and compare these results with that achievable in a single-ring resonator.