Session Y33: Quantum Photonics and Nonlinear Optics III

Clustering diffused-particle method for simulating electromagnetic fields among large ensembles of electromagnetically polarizable particles

In this work, the Foldy-Lax equation is generalized for a medium that consists of particles with both electric and magnetic responses. The result is used to compute fields scattered from ensembles of particles with polarizabilities extracted from shape/size effects, self-interaction, and dipole fluctuations. The computational complexity is reduced by hierarchical clustering techniques to enable simulations with on the order of 10¹⁰ particles. With so many particles we are able to see the transition to bulk media behavior of the fields. For non-magnetic materials, the observable index, permittivity, and permeability of the effective bulk medium are in good agreement with the Clausius-Mossotti relation. The fields simulated for particles with both electric and magnetic responses are in good agreement with new analytical results for a generalized effective medium theory.   

A guide to all-optical switching with epsilon-near-zero materials

Controlling light through all-optical means is central in fundamental and applied research. An important facet of this is switching one optical pulse by another. A promising avenue for all-optical switching is epsilon-near-zero (ENZ) materials, which have a region of wavelengths where the permittivity approaches zero. In nonmagnetic materials, the refractive index is related to the permitivity by n=√ε and the variation is then δn=δε/√ε. Therefore, ENZ materials will have large index changes even with small permittivity changes. One such class of materials is transparent conducting oxides (TCOs) whose ENZ regime occurs in the telecom range and have relatively small losses there.

Often all-optical switching experiments are performed exactly at the ENZ wavelength. However, we show this is not always optimal for all-optical switching, because of complex coupling of surface interactions. To investigate further, we first discuss the basic concepts of optically pumping ENZ materials composed of TCOs with the Drude model. Then we will describe common experimental configurations such as optically thick and thin ENZ films, ENZ films deposited on metallic and dielectric substrates, and the Kretschmann geometry. Finally, we willdiscuss the important role of losses in ENZ materials.   

Instantaneous optical forces in metamaterials

One important open aspect of the physics of metamaterials is the form of the optical force density. In this work, we investigate the optical force density in metamaterials based on instantaneous conservation laws of energy and momentum. We simulate light pulses in metamaterials in which the atoms are initially at rest and start to move as a result of the optical force density. We solve Newton's equation of motion to find out how the velocity of the medium under the influence of the optical force density is varying as a function of the position and time. We also study the assumptions used in the conventional derivation of electrostrictive forces, often discussed in optics literature. The theory of electrostriction, see e.g. Electrodynamics of Continuous Media by Landau and Lifshitz (1984), is based on changes in the volume of a dielectric under the influence of an external electromagnetic field. It is assumed that there is a thermodynamical balance between the dielectric and the external forces caused by the field. This assumption is no more valid at optical frequencies. Therefore, the possible role of electrostriction at optical frequencies is not obvious. Our work aims at revisiting the derivation to be consistent with the covariant theory of light in dispersive media.   

Multiple Dark Soliton Tracking and Sorting System: Combining Machine Learning with Physics

In cold atom experiments, data comes in the form of images which often suffer information loss, inherent in the techniques used to prepare and measure the system. Moreover, the use of traditional fitting-based analyses on these images necessitates additional processing, which leads to further information loss. This is particularly problematic when the processes of interest are complicated, such as interactions among excitations in Bose-Einstein condensates (BECs). In our work, we aim to identify and track kink solitons in BECs, which are associated with local decrease in condensate density. While the traditional approach performed well in finding locations of single solitons, it was not generalizable to more complex cases. To overcome this limitation, we propose a framework combining machine learning and traditional analyses to detect, locate, and characterize multiple solitonic excitations. In particular, we developed a Physics-Informed Excitation (PIE) classifier, which sorts solitonic excitations into categories (e.g., kink solitons, solitonic vortices or canted solitons) based on correlations between fitting parameters from image segments. This combined framework can be used to detect multiple solitons, extract physical parameters, and fine-classify each solitonic feature.   

Widely-tunable, doubly-resonant Raman scattering on diamond in an open microcavity

Raman lasers are a valuable resource for frequency conversion of coherent light. Diamond, in particular, is a material well-suited for Raman lasers due to the wide transparency window, high thermal conductivity and large Raman gain. Using conventional monolithic resonators, the implementation of a low-threshold Raman laser in the visible, however, has remained elusive due to material and fabrication limitations. In this work, we report a novel. In this work, we report a novel platform consisting of a diamond membrane embedded in an open-access Fabry-Perot microcavity, with quality factors exceeding 100 000. By establishing a doubly-resonant configuration, with the pump laser and the Raman transition simultaneously resonant, we demonstrate a strong enhancement of the Raman signal [1]. We further demonstrate a >THz continuous tuning range of doubly-resonant Raman scattering by exploiting the in situ tuning capability of our platform. We predict that with realistic improvements of our platform a sub-mW lasing threshold for visible wavelengths is within reach.  Our results pave the way for the creation of a universal low-power frequency shifter, a valuable addition to the nonlinear optics toolbox.

[1] S. Flagan et al, arXiv:2110.06242.   

Enhanced Photonic Maxwell's Demon with Correlated Baths

Since the Second Law of Thermodynamics development, several proposals to test its limits have been created. The thought experiment, known as Maxwell’s Demon, appeared as a system that could extract work or reduce the system’s entropy, using the Demon’s information with no energy consumption. Here we implement the first photonic Maxwell’s Demon with active feedforward where no post-selection is needed. The feedforward is implemented in a fiber-based system using Ultrafast optical switches that, given its versatility, allow us to implement the study in the single-photon level of several photon statistics as uncorrelated thermal baths (thermal light), split thermal beam, correlated (entangled states), and anticorrelated thermal baths (NOON states). Furthermore, this study shows that the classical correlations provided by quantum states can increase the Demon’s efficiency by almost one order of magnitude.   

Quantum Register Based on Si^29-Vacancy Defect in Diamond

Implementation of long range quantum networks requires quantum nodes with multiple interacting qubits which can be used to collect, store, and process information communicated via photonic channels. Silicon vacancy (SiV) centers in diamond photonic nanocavities are among the most promising candidate for such nodes due to their highly effective spin-photon interface. We present a novel system based on silicon-29 vacancy centers, combing a reproducible, predictable nuclear spin qubit as well as the SiV electronic spin with a single node. We demonstrate full coherent control of this 2-qubit register through quantum gates mediated by microwave and RF signals sent using on-chip coplanar waveguides. Using the strong coupling between the nuclear and electronic spins, we demonstrate fast, high-fidelity gates as well as individual initialization and readout of the qubits. These demonstrations pave the way for nuclear memory-enhanced quantum repeater protocols, as well as entanglement distillation protocols.   

Controlling the emission spectrum of a system in a dynamic environment with external field protocols

   Solid state quantum emitters or emitters in other dynamic environments play an essential in numerous fundamental applications from quantum information processing to quantum sensing. These applications may be hindered by spectral diffusion. The ransom drift of the emission spectrum of a quantum emitter in a dynamic environment with the surrounding fluctuations. In this talk, we consider the case of a quantum emitter subject to Gaussian fluctuations in its emission frequency as a function of time. We show that an external protocol applying a periodic sequence of pulses on the quantum emitters suppresses spectral diffusion, protecting the emission spectrum from the fluctuations in the environment. We further study an ensemble of quantum emitters, each with its own emission frequency in a Gaussian distribution of independent frequencies. The emission spectrum of this frequency is defined by the broad Gaussian distribution. However, under a periodic sequence of π-pulses, the emission spectrum of this ensemble is refocused to a central peak corresponding to the pulse carrier frequency.   

Understanding noise and decoherence of rare earth qubits in epitaxial oxide thin films

Erbium (Er³⁺) ions in solids are promising spin-photon interfaces for quantum networks and hybrid quantum architectures due to their long spin coherence times and telecom C band optical transitions. Epitaxial Er³⁺ doped Y₂O₃ thin films can be grown on silicon such that it enables large scale device integration for quantum technologies. We perform noise spectroscopy of erbium (Er³⁺) dopants in 100 nm epitaxial Y₂O₃ thin film with high sensitivity pulsed electron spin resonance (ESR) using superconducting microwave resonator and photoluminescence (PL) from an optical Fabry-Perot fiber cavity at milliKelvin temperatures. Both the optical linewidth measurements on single Er³⁺ ions and the spin coherence studies suggest spectral diffusions induced by the two-level-systems (TLS). We also show that dephasing due to TLS could be alleviated by an applied magnetic field. The current optical, microwave noise spectroscopy deepens our understanding of the decoherence mechanisms of rare-earth dopants in oxide thin films, and could lead to improvements in the coherence times and the coherent control of rare earth qubits in thin films.   

Engineering spin-photon quantum interfaces from erbium-oxygen complexes in silicon

Optically-interfaced spins in solids can enable quantum technologies, such as quantum networks, quantum transducers, and quantum sensors. The trivalent erbium ion (Er³⁺), coordinated with oxygen, could serve as a quantum light matter interface in the telecom band, as it has narrow optical transitions and long spin coherence in oxide hosts. Here, we are developing a spin-photon interface from erbium-oxygen (Er-O) complexes in silicon nanophotonics. Silicon-on-insulator wafers are implanted with Er⁺ and ¹⁶O⁺ and waveguides and cavities are fabricated using CMOS techniques. Photoluminescence, measured at ~4 Kelvin, reveals several sites between 1530-1540nm, with relaxation lifetimes of T₁~1.3ms. The emission rate is increased by coupling to a cavity with Q ~70,000 and mode volume ~0.042 um³. The measured Purcell enhancement is used to estimate the oscillator strength, spontaneous emission time, branching ratio, and the optical dipole moment of the transition. Hole burning is also used to measure narrow spectral diffusion linewidths. Furthermore, we will use superconducting micro-resonators to determine g-tensors and spin coherence. Scalable fabrication of Er-O doped silicon makes this platform promising for on-chip quantum technologies in the microwave and telecommunications band.   

EnhancedΧ(2) in CMOS-compatible Al1-xScxN thin films

Advancement in large-scale production of integrated photonic devices requires strongly nonlinear materials that are CMOS-compatible. While most materials require a trade-off between compatibility and nonlinearity, Al_1-xSc_xN is a CMOS-compatible alloy that exhibits enhanced second-order optical susceptibility (Χ⁽²⁾) with increased Sc concentration. Here, we present second harmonic generation measurements of Al_1-xSc_xN thin films that demonstrate greatly enhanced Χ⁽²⁾ values. For a sample with 36% Sc, we observe one Χ⁽²⁾ component, d₃₃, to have a value of 62.3±5.6 pm/V, which is increased by over an order of magnitude compared to intrinsic AlN and by a factor of two compared to lithium niobate. Though propagation loss also increases with Sc concentration, the percentage of Sc can be tuned for particular applications to balance loss and strong nonlinearity. The large Χ⁽²⁾ and CMOS-compatibility of this material make it a promising avenue for scalable production of nonlinear photonic devices.   

Unveiling the third order optical nonlinearities in NiCo2O4 nanoflowers

In this article, we demonstrate NiCo₂O₄ (NCO) as an efficient new nonlinear optical material with straightforward potential applications in optical limiting devices. We obtain nonlinear absorption coefficient (β) and nonlinear refractive index (n₂) in parallel by performing Z-scan technique, in both open and closed aperture configurations, respectively. To understand the mechanism responsible for third order optical nonlinearity in NCO, we excited the sample with contrasting laser pulse durations, 7 ns and 120 fs, at two different off-resonant wavelengths. For ns excitation, nonlinearity is mediated by excited state absorption (ESA) and free-carrier absorption, that gives rise to large β_ESA and positive n₂. On the other hand, when excited with fs laser, two-photon absorption (TPA) takes place and bound carriers induce strong negative n₂. The values obtained for β and n₂ in NCO are found to be higher among the family of well-known conventional transition metal oxides, therefore are promising for optics and other photonics applications.   

Designing hybrid VSe2-graphene oxide for ultrafast third-order nonlinear optical response

Third-order nonlinear optical absorption of light by materials is weak due to its perturbative nature, although a strong nonlinear response is crucial to applications in optical limiting and switching. A complex few-layer VSe₂/graphene oxide (GO) hybrid with strong interlayer coupling was prepared by a facile hydrothermal method. In this strongly coupled VSe₂/GO, we demonstrate experimentally and theoretically a strong ultrafast excited-state absorption (ESA) that is in stark contrast to the saturable absorption of semi-metallic VSe₂ and a weak two photon absorption of GO. Due to the extremely efficient charge transfer at ultrafast time scales between VSe₂ and GO, we observed the enhancement in the third-order nonlinear optical absorption by orders of magnitude compared to VSe₂ that shows saturable absorption and one order of magnitude compared to GO. Spectroscopic evidence of our study indicates that the optical signatures of VSe₂ and GO are modified in the hybrid, displaying direct coupling of both domains. To explain the results, we develop a rate-equation and numerically simulate the results. Using the strong ESA of our hybrid materials, we fabricate liquid cell-based high-performance optical limiters with important device parameters better than benchmark optical limiters.