Disorder in photonic crystals and waveguides creates states inside the photonic band gap. These states are often described as Lifshitz tails despite exhibiting energy distributions inconsistent with Lifshitz statistics near the band edge. Here we show that in photonic-crystal waveguides with intentionally engineered anisotropic disorder, the band-edge tail accessible experimentally follows an Urbach law universally, with cumulative statistics F(Δ)=exp[-(Δ/α)^β], where Δ is the spectral detuning from the band edge, and an exponent β≈ 1 independent of disorder strength and orientation. In contrast to Lifshitz behavior, the density of states is maximal at the band edge and decays into the gap. Crucially, we find that the Urbach energy α is anisotropic, with a pronounced directional splitting and qualitatively different scaling for disorder parallel and perpendicular to the waveguide axis. These conclusions are supported by quantitative agreement between optical measurements of GaAs photonic-crystal waveguides and full-vector simulations. The anisotropic Urbach energy emerges as a sensitive probe of disorder-mode coupling and a practical metric to characterize structural disorder in photonic devices.

Quantum photonic integrated circuits represent a promising pathway for advancing quantum technologies, but their realization hinges on efficient on-chip detection of single photons. Superconducting nanowire single-photon detectors (SNSPDs) based on NbTiN offer high detection efficiencies and low jitter. Yet, integration challenges persist, especially on platforms like GaAs. In particular, very limited data exist about the optical properties of NbTiN. This paper reports on measurements of structural and optical properties of NbTiN thin films deposited on GaAs and Si substrates.

We present a rigorous analysis that combines theory, simulation, and experimental measurements to quantify the relationship between strain and bandgap in two dimensional gallium selenide (Ga_2Se_2). Experimentally, we transfer thin Ga_2Se_2 flakes onto patterned substrates to deterministically induce multiaxial localized strain. We quantify the local strain using a combination of atomic force microscopy (AFM) measurements and COMSOL Multiphysics simulation. We then experimentally map the strain-induced bandgap shifts using high-resolution hyperspectral PL imaging to generate a robust and statistically significant dataset. We systematically fit this data to extract gauge factors that relate the bandgap shift to the local uniaxial and biaxial strain. We then compute the uniaxial and biaxial strain gauge factors via density functional theory (DFT) and find excellent agreement with the experimentally-determined values. Finally, we show that a simple model that computes bandgap shifts from the local uniaxial and biaxial strain predicts the observed multiaxial bandgap shift with less than 10% error. The combined results provide a framework for deterministic realization of tailored bandgap profiles induced by controlled strain applied to Ga_2Se_2, with implications for the future realization of localized quantum emitters for quantum photonic applications.

Altermagnets host momentum-selective spin splitting and chiral-split magnonic excitations despite vanishing net magnetization, enabling spin transport without ferromagnetism. In rutile structures, establishing altermagnetism spectroscopically has been challenging, motivating the search for a rutile platform with a resolvable exchange-driven chiral magnon splitting. Here we combine hybrid-functional first-principles calculations with linear spin-wave theory to show that rutile CuF_2 exhibits a meV-scale splitting between magnon modes of opposite chirality along momentum directions dictated by its d-wave altermagnetic symmetry. The splitting originates from an anomalously strong long-range super-superexchange channel Cu–F⋯F–Cu, which enhances the symmetry-allowed difference between seventh-neighbour exchanges, J_7b - J_7a, controlling the chiral-mode splitting. We identify an orbital-resonance mechanism: energetic alignment between Cu 3d_z^2 and F 2p_z states strengthens virtual hopping along the Cu–F⋯F–Cu path and amplifies the anisotropic long-range exchange. Rutile CuF_2 therefore provides an ideal platform to validate rutile altermagnetism and suggests an orbital-energy description for engineering large chiral magnon splittings in insulating altermagnets.

Emerging classical and quantum device concepts demand precise spatial control over the optoelectronic properties of two-dimensional (2D) materials, but deterministic engineering via local multiaxial strain distributions remains challenging. Using Ga_2Se_2, we demonstrate a material-agnostic platform in which nanostructure geometry deterministically prescribes in-plane strain profiles in suspended van der Waals membranes. We first use hyperspectral photoluminescence mapping and experimentally-constrained finite element analysis to quantify the experimental biaxial and uniaxial strain gauge factors that relate strain to the change in bandgap. We next show that a two-component analytical model can predict, with less than 12

Cavity-mediated strong coupling is an essential tool for quantum photonics. However, the inherent inhomogeneity in ensembles of matter-based qubits necessitates independent tuning to bring more than one qubit into resonance with a single cavity mode. We present the design, fabrication, and characterization of a GaAs-based photonic crystal split cavity that consists of two electrically-distinct portions, which preserves the ability to apply independent electric fields that would independently tune two distinct qubits based on InAs Quantum Dots (QDs) into resonance with a cavity mode. We show that this device, despite the cut required to electrically isolate the two halves, achieves an average Q ≥ 20,000, sufficient to enter the strong coupling regime. Moreover, we show that the Q is limited primarily by the precision and accuracy of the e-beam lithography tool, rather than by sidewall scattering. This result creates a realistic experimental path toward devices that use controlled interactions between two InAs QDs, mediated by strong coupling to a single cavity mode, to generate multi-dimensional photon graph states.

Disorder in photonic lattices creates localized states inside the photonic band gap. The energy distribution of these states is often described as a Lifshitz tail, even though it is inconsistent with Lifshitz statistics near the band edge. Here, we show that in photonic-crystal waveguides with intentionally engineered anisotropic disorder, the band-edge tail accessible experimentally follows an Urbach law, with cumulative statistics F(Δ)=exp[−(Δ/α)^{β}], where Δ is the spectral detuning from the band edge, and an exponent β≈1 independent of disorder strength and orientation. In contrast to Lifshitz behavior, the density of states is maximal at the band edge and decays into the gap. Crucially, we find that the Urbach energy α is anisotropic, with a pronounced directional splitting and qualitatively different scaling for disorder parallel and perpendicular to the waveguide axis. These conclusions are supported by quantitative agreement between optical measurements of GaAs photonic-crystal waveguides and full-vector simulations. The anisotropic Urbach energy emerges as a sensitive probe of the coupling between structural disorder and the guided Bloch mode, and a practical metric to characterize structural disorder in photonic devices.

We theoretically investigate the intrinsic magnon orbital Nernst effect (ONE) in noncollinear antiferromagnets with kagome spin systems. Our analysis reveals that an externally applied magnetic field induces topological phase transitions in the magnonic system, characterized by the closing and reopening of the band gap between distinct magnon bands. These transitions enable tunable control of the magnon ONE with applied magnetic field, with a pronounced enhancement in magnon orbital Nernst conductivity near the phase transition points. This tunability presents a promising direction for experimental detection of the magnon ONE.

Measurement-based quantum computing offers a promising route towards scalable, universal photonic quantum computation. This approach relies on the deterministic and efficient generation of photonic graph states in which many photons are mutually entangled with various topologies. Recently, deterministic sources of graph states have been demonstrated with quantum emitters in both the optical and microwave domains. In this work, we demonstrate deterministic and reconfigurable graph state generation with optical solid-state integrated quantum emitters. Specifically, we use a single semiconductor quantum dot in a cavity to generate caterpillar graph states, the most general type of graph state that can be produced with a single emitter. By using fast detuned optical pulses, we achieve full control over the spin state, enabling us to vary the entanglement topology at will. We perform quantum state tomography of two successive photons, measuring Bell state fidelities up to 0.80±0.04 and concurrences up to 0.69±0.09, while maintaining high photon indistinguishability. This simple optical scheme, compatible with commercially available quantum dot-based single photon sources, brings us a step closer to fault-tolerant quantum computing with spins and photons.

There is strong interest in designing and realizing optically active semiconductor nanostructures of greater complexity for applications in fields ranging from biomedical engineering to quantum computing. While these increasingly complex nanostructures can implement progressively sophisticated optical functions, the presence of more material constituents and interfaces also leads to increasingly complex exciton dynamics. In particular, the rates of carrier trapping and detrapping in complex heterostructures are critically important for advanced optical functionality, but they can rarely be directly measured. In this work, we develop a model that includes the trapping and release of carriers by optically inactive states. The model explains the widely observed biexponential decay of the photoluminescence signal from neutral excitons in low-dimensional semiconductor emitters. The model also allows determination of likelihood intervals for all of the transition rates involved in the emission dynamics, without the use of approximations. Furthermore, in cases for which the high-temperature limit is suitable, the model leads to specific values of such rates, outperforming the reduced models previously used to estimate those quantities. We demonstrate the value of this model by applying it to time-resolved photoluminescence measurements of CdSeTe/CdS heterostructures. We obtain values not only for the radiative and nonradiative lifetimes but also for the delayed photoluminescence originating in trapping and release.

We report the design of and progress towards devices that integrate NbTiN superconducting nanowire single-photon detectors with GaAs nanophotonic devices. We show that the design is expected to achieve photon detection efficiency of 99.41% power absorption in a 10-mu m-long nanowire with minimized external coupling losses.

The orbital degree of freedom has recently attracted significant attention due to the novel phenomena it enables in condensed matter systems. However, the interpretation of the orbital degree of freedom in bosonic quasiparticles remains conceptually ambiguous and the mechanisms governing the transfer of orbital angular moment (OAM) between distinct quasiparticles, such as magnons and phonons, are not yet fully understood. We investigate orbital dynamics in bosonic systems and identify two origins of OAM: (i) global rotational motion of the system, and (ii) the quantum geometry of wavefunctions. Focusing on the latter, we study strongly coupled magnon-phonon systems in two-dimensional antiferromagnets as a test case. We uncover finite OAM arising from quantum geometric effects via two mechanisms: (a) time-parity symmetry breaking, yielding intra band OAM, and (b) interband coupling, generating interband OAM. We propose that an electrical detection scheme based on the transverse voltage generated by hybrid magnon phonon modes can be used to experimentally probe the bosonic orbital degree of freedom. Our results establish a foundation for the emerging field of phonon orbitronics, providing both a conceptual bridge between phonon and magnon orbitronics and a tool for better understanding magnon-polarons. They also advance a unified framework for harnessing orbital degrees of freedom in bosonic systems and pave the way toward electrical control of magnetization and phononic transport.

Magnons offer a promising path toward energy-efficient information transmission and the development of next-generation classical and quantum computing technologies. However, efficiently exciting, manipulating, and detecting magnons remains a critical need. We show that magnons, despite their charge-neutrality, can induce electric polarization through their spin and orbital moments. This effect is governed by system symmetry, magnon band hybridization, and interactions with other quasiparticles. We calculate the electric polarization induced by magnons in two-dimensional collinear honeycomb and noncollinear antiferromagnets (AFMs), showing that the presence of the Dzyaloshinskii-Moriya interaction yields a finite net electric polarization. In NiPSe3, a collinear honeycomb AFM with Zigzag order, the induced net electric polarization is about three orders of magnitude greater than in MnPS3, a collinear honeycomb AFM with Néel phase. In the noncollinear AFM KFe3(OH)6(SO4)2, the net electric polarization can be tuned via magnon hybridization, which can be controlled by external magnetic fields. These findings reveal that electric fields could be used to both detect and manipulate magnons under certain conditions by leveraging their spin and orbital angular moment. They also suggest that the discovery or engineering of materials with substantial magnon orbital moments could enhance practical uses of magnons for future computing and information transmission applications.

Gallium selenide (Ga2Se2) is a promising 2D material for use in both classical and quantum photonic device technologies because it transitions to a direct bandgap as a function of both increasing film thickness and applied strain. However, the optical emission from thin exfoliated Ga2Se2 films has been reported to degrade rapidly, which would severely limit its usefulness for optoelectronic applications. We perform a systematic time-dependent study of the intensity of photoluminescence emitted from exfoliated Ga2Se2 as a function of both the sample preparation and storage conditions. We find that the degradation of optical properties is substantially slower than previously reported. We further find that the degradation is a surface effect that begins upon transient exposure to air and that the degradation cannot be mitigated by any reasonable sample storage conditions. Finally, we show that the optical degradation can be eliminated by utilizing hexagonal boron nitride (h-BN) encapsulation in a glovebox to protect the Ga2Se2 from even momentary air exposure.

Cadmium oleate is widely used as a cation precursor in the synthesis of cadmium chalcogenide nanocrystal quantum dots (QDs) for a broad range of photonic and optoelectronic applications. Cd oleate can noncovalently assemble to form a supramolecular coordination gel, or metallogel, in solvents commonly used to disperse oleate-capped QDs. The gelation severely impedes the purification of oleate-capped QDs from excess Cd oleate, resulting in a gelled product that cannot be reliably characterized or used in further synthesis reactions. Here, we investigate the Cd oleate gel to gain insights into its viscoelastic properties and behavior under conditions relevant to QD synthesis, purification, and storage. We then examine how to effectively mitigate gelation by adding oleylamine as an additional ligand to disrupt noncovalent assembly. We synthesize PbS/CdS core/shell QDs via cation exchange as a case study to illustrate gelation of the reaction product and further demonstrate how this issue can be resolved through a better understanding of the supramolecular gel.

Colloidal semiconductor quantum dot heterostructures are an attractive platform for photon upconversion in solar energy applications due to their wide absorption bandwidths and highly tunable optical properties. NIR-to-visible photon upconversion has been previously demonstrated in PbS/CdS/CdSe core/multishell heterostructures, but their reported upconversion efficiencies are low. The upconversion performance could be significantly improved by engineering the PbS/CdS core/shell intermediate structure to achieve the quasi-type II band structure and carrier separation behavior known to promote the upconversion process. Here we address two critical challenges to realizing an optimized PbS/CdS intermediate structure that could enable efficient upconversion in full PbS/CdS/CdSe structures. We first use computational simulations to predict the band alignment and carrier behavior in PbS/CdS and PbS/CdS/CdSe as a function of PbS core size and CdS shell thickness. We use the results to develop synthesis targets for PbS/CdS predicted to achieve effective carrier separation and improved upconversion performance. Next, we synthesize a library of PbS/CdS quantum dots via cation exchange across three particle sizes. We analyze the reaction products using absorbance, PL, and transmission electron microscopy to create a framework for the predictive synthesis of PbS/CdS with the target core and shell dimensions. Finally, we combine our computational and experimental findings to identify and understand a trade-off in design and synthetic factors required to realize PbS/CdS structures that provide a foundation for efficient NIR-to-visible upconversion.

Terahertz (THz) radiation (0.3 to 30 THz) fills the crucial gap between the microwave and infrared spectral range. THz technology is important for applications ranging from imaging to telecommunication to biosensing, but these applications often require precise control and manipulation of the THz frequency and polarization state, which typically requires modulators external to the THz source. A hybrid THz emitter that overcomes this limitation by integrating two THz emitters into a single device to enable pulse shaping and chirality control of the emitted radiation without any external components is demonstrated. The two sources are a spintronic emitter (SE) and a semiconductor photoconductive antenna (PCA). The two emitters respond independently to external parameters: the PCA is controlled by the applied bias voltage, while the SE is controlled by the applied magnetic field. Moreover, a dual-wavelength excitation scheme allows for control of the relative time delay between the THz emission from each constituent. These properties of the hybrid emitter enable precise control of the mixing of the two signals to control the frequency, polarization, and chirality of the overall THz radiation. This on-chip hybrid emitter thus provides a powerful platform for engineered THz radiation with wide-ranging potential applications.