arXiv subjects

Jonathan J. Finley

Publications and source records attributed to Jonathan J. Finley.

At least 19 recordsLinked to original sources

arXiv2026

The Hidden Cost of Alloying: Disorder-Driven Transport Collapse in TMDs

Alloying in two dimensional semiconductors is widely used to tune bandgaps, yet its implications for charge and energy transport remain poorly understood. Here, we investigate MoS2xSe2(1-x) alloys as a model system to study the interplay between composition, thickness, and disorder. Optical transitions and valence band dispersions evolve continuously with both stoichiometry and number of layers, with negligible bandgap bowing and a composition dependent attenuation of thickness driven renormalization. In contrast, time resolved spatial mapping of photoexcited carriers reveals a pronounced and asymmetric collapse of carrier diffusivity at intermediate compositions, which cannot be accounted for by changes in effective mass or band alignment, and instead emerges from strong real space fluctuations in the local energetic landscape generated by random chalcogen substitution. Microscopic simulations reproduce the experimental trends and show that the character of disorder depends critically on the direction of alloying, producing either scattering barriers or deep trapping sites. Together, these results demonstrate that transport in TMD alloys is governed by disorder physics, overlooked by conventional optical and photoemission probes at equilibrium. Our findings establish transport as a stringent metric of electronic quality and high-light intrinsic limitations in the usage of TMD alloys for layered semiconductor devices.

cond-mat.mtrl-sci↗

arXiv2026

Dual-Trigger of Series Nanowire Detector for Event-Based Photon Number Assignment

Photon-number-resolving (PNR) detectors are essential components of photonic quantum technologies. However, conventional single-channel edge-triggered readout struggles to resolve the photon number $n$ in real time or to characterize how timing jitter depends on $n$. In this work, we use a dual-trigger method on a three-pixel series-connected superconducting nanowire single-photon detector (SNSPD) that triggers on both the rising and falling edges of the detection pulse. By doing so, we preserve the precise arrival time of the detection event while mapping the photon number onto the time interval between the rising and falling edges, allowing clear separation of the events. Using this technique, we assign each detection event to $n = 1, 2,$ or 3 photons with $99\,\%$ posterior confidence across all three classes. The timing jitter decreases as $n$ increases, reaching values below $41\, \text{ps}$ for $n \geq 2$. Comparing edge-triggering with constant-fraction discrimination (CFD) for arrival-time extraction, we find that CFD yields lower jitter for single-photon events and a nearly constant mean arrival time. Altogether, our results establish dual-triggering as a robust, low-latency readout scheme for PNR detectors, while revealing a photon-number dependence of the timing jitter relevant to timing precision achievable in heralded photonic quantum applications.

quant-ph↗

arXiv2026

Tunable g-Factors of Hybridized Orbitals in a Quantum Dot Molecule

The ability to control the $g$-factors of orbital spin states in optically active quantum dot molecules (QDMs) is a prerequisite for the high-fidelity generation of multi-photonic cluster states with higher-dimensional entanglement structure. Protocols that rely on two coupled spins require knowledge of the $g$-factor and its dependence on external control parameters. Mismatches in the $g$-factor between tunnel-coupled dots introduce unwanted dephasing of coupled spin-states, making precise characterization and voltage control essential. Here, we measure the gate voltage dependence of the electron and hole $g$-factors of negatively charged trions $X^{-}$ in a single InGaAs QDM using polarization-resolved magneto-photoluminescence spectroscopy. The electron $g$-factor exhibits a pronounced step-like change at the tunneling resonance, shifting from $g_\mathrm{e} = -0.336\pm 0.008$ to $g_\mathrm{e} = -0.389\pm 0.003$, providing a direct spectroscopic fingerprint of molecular orbital formation and a shift of the wavefunction localization from the lower to the upper dot. In contrast, the hole $g$-factor remains nearly constant at $g_\mathrm{h} \approx 0.094 \pm 0.007$, exhibiting a weak modulation near the anticrossing voltages attributed to Coulomb-mediated deformation of the wavefunction by the tunneling electron. Our results are quantitatively reproduced by an eight-band $\mathbf{k}{\cdot}\mathbf{p}$ model, establishing electric-field control of the trion $g$-factors as a practical tool for independently tuning the Zeeman splitting of individual dots and opening new pathways towards the deterministic generation of two-dimensional photonic cluster states.

cond-mat.mes-hall↗

arXiv2026

Valley polarization of moir\'e interlayer exciton complexes driven by many-body interactions

Localized interlayer excitons (IX) in moir\'e transition metal dichalcogenide heterostructures can both probe and participate in many-body states hosted by the moir\'e superlattice. When the IX density is small compared to the moir\'e lattice density, the formation of incompressible charge crystals at fractional electronic moir\'e fillings modifies exciton-charge scattering, leading to enhanced lifetimes in photoluminescence (PL) measurements. At high IX densities, the exciton dynamics are altered by the emergence of an excitonic Mott insulator and the formation of doubly-occupied sites (IXX). Here, we investigate the IX PL lifetime and valley polarization in an R-type $\mathrm{WSe_2}$/$\mathrm{WS_2}$ bilayer across a wide range of IX and charge densities. While previous studies reported a decrease of polarization in time-integrated measurements in charge-incompressible phases, our results show that this arises not from enhanced intervalley scattering, but from a dilution of the valley polarization by the dramatic enhancement of IX lifetimes. At high excitation densities, we probe the dynamics of the IXX and show that despite the nominal antiparallel valley configuration of the two constituent excitons, a strong, anomalous valley polarization develops as the IXX population decays. Our results shed light on the complex exciton and valley dynamics of IX and demonstrate that they are strongly modified by the rich many-body physics of moir\'e heterobilayers.

cond-mat.mes-hall↗

arXiv2026

Monolithic axial InGaAs quantum dot emitters in GaAs-based nanowires via Sb-mediated facet engineering

GaAs-based nanowires hosting active quantum heterostructures provide a promising route toward monolithic integration of single-photon sources on silicon, a key requirement for scalable quantum photonics. However, ultrathin axial quantum-emitter formation is often hindered by facet-dependent growth dynamics and rotational twins, which induce lateral overgrowth and compromise interface abruptness. Here, we develop InGaAs-based quantum emitters by tailoring facet evolution via dilute Sb incorporation, which efficiently suppresses twins and promotes confined axial insertion at the growth-front facet. This approach significantly enhances the probability of obtaining abrupt, few-nanometer-thin quantum dots at the nanowire tip. Single-nanowire optical spectroscopy reveals intense, spatially localized emission from the active region with lifetimes as short as (0.51 $\pm$ 0.02) ns, and second-order photon-correlation measurements consistently exhibit pronounced antibunching with $g^{(2)}(0)<0.4$, confirming single-photon emission. These results establish a strong correlation between twin density and axial heterostructure formation, identifying defect control as a key factor in realizing monolithically integrated nanowire single-photon sources.

physics.app-ph↗

arXiv2026

Molecular beam epitaxy of wafer-scale O-band InAs/InGaAs quantum dots on GaAs for quantum photonics

We report a scalable molecular beam epitaxy strategy to achieve a low density of O-band electrically tunable InAs/InGaAs quantum dots (QDs) on GaAs(001) substrates. Our approach is based on a gradient deposition of InAs in the sub-ML regime and subsequent capping with an InGaA strain-reducing layer to redshift the emission wavelength. For different growth conditions, we investigate the optical properties of the dots using photoluminescence mapping and correlate with structural properties determined by scanning transmission electron microscopy. Using a surface roughness modulation technique and synchronizing InAs sub-monolayer deposition cycles with substrate rotation, we control the dot density and position low-density regions (< 1 QD per um^2) on the substrate. Hyperspectral imaging is used to map the spatial and spectral characteristics of many individual dots in the low-density region, confirming that our approach is universally applicable to conventional MBE growth on (001) surfaces. Finally, we tune the QD emission wavelength within the O-band using electric fields and demonstrate single-photon emission with g(2)(0) = 0.020(14).

cond-mat.mtrl-sci↗

arXiv2026

Ultrafast Formation and Annihilation of Strongly Bound, Anisotropic Excitons

Van der Waals (vdW) layered materials with long-range magnetic order have the potential to enable novel optoelectronic and spintronic applications. Among these, CrSBr is an air-stable, direct band gap semiconductor that hosts interlayer antiferromagnetic order, a highly anisotropic electronic structure, and strongly bound excitons. In particular, excitons in CrSBr have been shown to inherit the quasi-one-dimensional nature of the material and also couple to the underlying spinorder. However, mechanisms of exciton formation, dissociation, and interaction with free carriers remain largely unexplored, despite being crucial for spintronic and optoelectronic applications. Here, we employ time- and angle-resolved photoemission spectroscopy to map the electronic structure and excited state dynamics in CrSBr. We directly resolve an exceptionally large exciton binding energy (~800 meV) and a highly anisotropic momentum space distribution of the exciton, revealing its quasi-1D real-space character. We observe an excitation-density-dependent interconversion between bound excitons and quasi-free carriers on sub- to few-picosecond timescales, indicating that many-body effects govern the excited-state dynamics and optical properties during the initial stages of relaxation. Our work highlights the strongly bound, anisotropic character of excitons in CrSBr, as well as the microscopic interactions steering relaxation pathways after photoexcitation in elevated density regimes relevant for future device applications.

cond-mat.mtrl-sci↗

arXiv2025

Mitigating the Transition of SiV$^-$ in Diamond to an Optically Dark State

Negatively charged silicon vacancy centers in diamond (SiV$^-$) are promising for quantum photonic technologies. However, when subject to resonant optical excitation, they can inadvertently transfer into a zero-spin optically dark state. We show that this unwanted change of charge state can be quickly reversed by the resonant laser itself in combination with static electric fields. By defining interdigitated metallic contacts on the diamond surface, we increase the steady-state SiV$^-$ photoluminescence under resonant excitation by a factor $\ge3$ for most emitters, making it practically constant for certain individual emitters. We electrically activate single \sivs near the positively biased electrode, which are entirely dark without applying local electric fields. Using time-resolved 3-color experiments, we show that the resonant laser not only excites the SiV$^-$, but also creates free holes that convert SiV$^{2-}$ to SiV$^-$ on a timescale of milliseconds. Through analysis of several individual emitters, our results show that the degree of electrical charge state controllability differs between individual emitters, indicating that their local environment plays a key role. Our proposed electric-field-based stabilization scheme enhances deterministic charge state control in group-IV color centers and improves its understanding, offering a scalable path toward quantum applications such as entanglement generation and quantum key distribution.

quant-ph↗

arXiv2025

Second-order Stark shifts exceeding 10$\,$GHz in electrically contacted SiV$^-$ centers in diamond

Negatively charged silicon vacancy centers (SiV$^-$) in diamond exhibit excellent spin coherence and optical properties, making them promising candidates for quantum technologies. However, the strain-induced inhomogeneous distribution of optical transition frequencies poses a challenge for scalability. We demonstrate electrical tuning of the SiV$^-$ center zero-phonon lines using in-plane contacts to apply moderate electric fields up to 45$\,$MV/m. The second-order Stark shift exceeds 10$\,$GHz, which is of the same order of magnitude as the 15$\,$GHz inhomogeneous distribution of SiV$^-$ observed in emitters embedded in optical nanostructures such as photonic crystal nanocavities. Analysis of individual SiV$^-$ centers shows significant variation in polarizabilities between defects indicating that the polarizability strongly depends on local parameters like strain. The observed polarizabilities are 3-25 times larger than those of tin vacancy centers, which we attribute to valence band resonances that delocalize the $e_u$ wavefunctions. Photoluminescence excitation measurements reveal that optical linewidths increase moderately with applied electric field strength. Our results demonstrate that large electrical Stark shifts can overcome the inhomogeneous distribution of transition frequencies, representing a significant step toward scalable SiV$^-$-based quantum technologies such as quantum repeaters.

quant-ph↗

arXiv2025

Engineering strong correlations in a perfectly aligned dual moir\'e system

Exotic collective phenomena emerge when bosons strongly interact within a lattice. However, creating a robust and tunable solid-state platform to explore such phenomena has been elusive. Dual moir\'e systems$-$compromising two Coulomb-coupled moir\'e lattices$-$offer a promising system for investigating strongly correlated dipolar excitons (composite bosons) with electrical control. Thus far, their implementation has been hindered by the relative misalignment and incommensurability of the two moir\'e patterns. Here we report a dual moir\'e system with perfect translational and rotational alignment, achieved by utilizing twisted hexagonal boron nitride (hBN) bilayer to both generate an electrostatic moir\'e potential and separate MoSe$_{2}$ and WSe$_{2}$ monolayers. We observe strongly correlated electron phases driven by intralayer interactions and identify interlayer Rydberg trions, which become trapped in the presence of the Mott insulating state. Importantly, our platform is electrostatically programmable, allowing the realization of different lattice symmetries with either repulsive or attractive interlayer interactions. In particular, we implement the latter scenario by optically injecting charges, which form a dipolar excitonic phase. Our results establish a versatile platform for the exploration and manipulation of exotic and topological bosonic quantum many-body phases.

cond-mat.mes-hall↗

arXiv2025

Single-Photon Detection in Few-Layer NbSe$_2$ Superconducting Nanowires

Superconducting Nanowire Single-Photon Detectors (SNSPDs) are key building blocks for photonic quantum technologies due to their ability to detect single photons with ultra-high efficiency, low dark counts and fast temporal resolution. Superconducting materials exhibiting high uniformity, large absorption cross-section and atomic-scale thickness are desirable to extend single-photon detection from the near-infrared up to the terahertz regime, where existing material choices are especially constrained. Substrate independence would further open the way to integrate detectors onto functional materials and heterostructures, enhancing performance and enabling proximal read-out of a wide range of individual excitations. Here, we top-down shape the prototypical two-dimensional superconductor niobium diselenide (NbSe$_2$) into few-layer nanowires less than 100 nm wide and demonstrate single-photon detection at 780 and 1550 nm. At the same time, the dark-count rate remains below 1 Hz up to the switching current and we achieve a timing jitter below 50 ps. We use a diffusive hot-spot model to estimate a theoretical cut-off wavelength that surpasses the millimetre range. Our results open up routes toward quantum limited detectors integrated into quantum-photonic circuits and quantum devices, with the potential for novel detection capabilities and unprecedented energy sensitivity.

cond-mat.supr-con↗

arXiv2025

Deterministic Control of Photon-Number Probabilities via Phase-Controlled Quantum Interference

Deterministically tailoring optical Fock states beyond the single-photon level is crucial for boson sampling, loss-tolerant photonic qubits, and quantum-enhanced sensing, however has yet remained elusive. Here, we report an all-linear-optical protocol that converts a resonantly driven single-photon emitter into a deterministic generator of vacuum--single-photon--two-photon states. A phase-stabilized, path-unbalanced Mach-Zehnder interferometer combines vacuum--single-photon interference and Hong-Ou-Mandel effect, providing two knobs to shape photon-number probabilities. By tuning these knobs, we observe a dynamic transition from antibunching to strong bunching in correlation measurements. A fully quantum-mechanical, discrete time-bin model maps these results onto the tailored photon statistics. The same framework predicts that two indistinguishable emitters would extend the accessible space to deterministic NOON states and single-photon filtering. This protocol relying on linear optics and available single-photon sources provides a scalable, chip-compatible, and platform-independent route to on-demand and deterministic few-photon resources for quantum metrology, photonic computing, as well as long-distance quantum networks.

quant-ph↗

arXiv2025

Ferroelectric Control of Interlayer Excitons in 3R-MoS$_{2}$ / MoSe$_{2}$ Heterostructures

We investigate the interaction between interlayer excitons and ferroelectric domains in hBN-encapsulated 3R-MoS$_2$/MoSe$_2$ heterostructures, combining photoluminescence experiments with density functional theory and many-body Green's function calculations. Low-temperature photoluminescence spectroscopy reveals a strong redshift of the interlayer exciton energy with increasing MoS$_2$ layer thickness, attributed to band renormalization and dielectric effects. We observe local variations in exciton energy that correlate with local ferroelectric domain polarization of the 3R-MoS$_2$ layer, showcasing distinct domain-dependent interlayer exciton transition energies. Gate voltage experiments demonstrate that the interlayer exciton energy can be tuned by electrically induced domain switching. These results highlight the potential for interlayer exciton control by local ferroelectric order and establish a foundation for future ferroelectric optoelectronic devices based on van der Waals heterostructures.

cond-mat.mtrl-sci↗

arXiv2025

Temperature-Dependent Emission Spectroscopy of Quantum Emitters in Hexagonal Boron Nitride

Color centers in hexagonal boron nitride (hBN) have attracted significant interest due to their potential applications in future optical quantum technologies. For most applications, scalable on-demand fabrication is a key requirement. Recent advances using localized electron irradiation have demonstrated near-identical emitters in the blue and yellow spectral regions. While the blue emitters have been demonstrated in cryogenic temperatures, the yellow emitters remain uncharacterized under such conditions. In this work, we therefore extended the study of yellow emitters to cryogenic temperatures. Initially, multiple spectral features were observed, prompting a systematic investigation that led to the identification of a defect emission centered around 547.5 nm with high brightness and excellent photostability. By tuning the excitation wavelength, we are able to distinguish Raman scattering peaks from the emitter emission. Further analysis of the vibronic emissions allowed us to identify an optical phonon mode, whose contribution becomes increasingly dominant at elevated temperatures. Photoluminescence excitation spectroscopy (PLE) reveals excitation through this phonon mode enhances the emission by almost 5-fold in cryogenic temperature. Temperature-dependent studies further elucidate the role of phonons in the emission process. These observations deepen our understanding of the nature of the emitters, opening new avenues for precise tuning of quantum light sources.

physics.optics↗

arXiv2025

Unraveling Quantum Size-Dependent Optoelectrical Phenomena in Hot Carrier Quantum Well Structures

The enhancement of power conversion efficiency beyond the theoretical limit of single-junction solar cells is a key objective in the advancement of hot carrier solar cells. Recent findings indicate that quantum wells (QWs) can effectively generate hot carriers by confining charged carriers within their potential wells and by optimizing material properties. Here, we investigate the impact of quantum confinement on the thermodynamic properties of photogenerated hot carriers in p-i-n InGaAs/InAlAs heterostructure diodes, utilizing QW thicknesses of 4 nm, 5.5 nm, and 7.5 nm. The optical properties of these nanostructures reveal significant hot carrier effects at various lattice temperatures, with a pronounced effect noted at lower temperatures. The experimental results indicate that the widest QW exhibits stronger hot carrier effects than the thinner QWs. Additionally, the open-circuit voltage of the samples demonstrates a correlation with the degree of quantum confinement, mirroring trends observed in the quasi-Fermi level splitting of hot carriers. However, the magnitudes recorded exceed the bandgap of the quantum structures, suggesting that this behavior may be influenced by the barrier layer. Furthermore, the short-circuit current of the samples reveals a strong dependence on excitation power, but not on the degree of quantum confinement. This indicates that the majority of the photocurrent is generated in the barrier, with negligible contributions from photogenerated carriers within the QWs. This study provides insights into the role of quantum confinement on the opto-electrical properties of non-equilibrium hot carrier populations in QW structures.

physics.app-ph↗

arXiv2025

Selective filtering of multi-photon events from a single-photon emitter

Single-photon purity is one of the most important key metrics of many quantum states of light. For applications in photonic quantum technologies, e.g. quantum communication and linear optical quantum computing, a minimization of the multi-photon error rate is required because of its error-introducing nature. Ultimately, the purity of state-of-the-art single-photon sources was found to be limited by spontaneous emission and subsequent reexcitation during the interaction with the driving field. Here, we demonstrate that even this fundamental limit to the single-photon purity can be overcome due to the distinct spectro-temporal properties of the individual photons forming multi-photon errors. For driving pulses shorter than the emitter lifetime, we find that photons emitted during the pulse exhibit a significantly broader spectral shape than the emitter's natural linewidth. Thus, we can selectively filter out the majority of this instantaneously emitted photon by employing narrowband spectral filters which reduces the measured degree of second-order coherence at zero time delay by almost one order of magnitude. This enables a significant suppression of the multi-photon error rate without detrimental effects on the desired single-photon emission.

quant-ph↗

arXiv2025

Dynamically Dressed States of a Quantum Four-Level System

In this work, we experimentally and theoretically study the dressed-state emission of the biexciton-exciton cascade in a semiconductor quantum dot under pulsed, resonant, two-photon excitation. Building on the well-characterized steady-state dressed emission of the four-level system, we examine its dynamic counterpart under pulsed, resonant excitation, addressing both experimental observations and theoretical modeling. Here we report several sidebands emerging from the biexciton-to-exciton transition, whose number and spectral width depend on the excitation pulse duration and the effective pulse area, while no sidebands emerge from the exciton-to-ground-state transition. Since the biexciton state population follows a nonlinear pulse area function, sidebands with a small spectral nonlinearity result. Detuning- and time-dependent measurements provide deeper insight into the emission properties of the dressed states. They show that side peak emission only occurs in the presence of the excitation pulse. Moreover, when the system is excited by a Gaussian-shaped laser pulse, side peak emission takes place sequentially.

quant-ph↗

arXiv2025

Resonant and Anti-resonant Exciton-Phonon Coupling in Quantum Dot Molecules

Optically active quantum dot molecules (QDMs) can host multi-spin quantum states with the potential for the deterministic generation of photonic graph states with tailored entanglement structures. Their usefulness for the generation of such non-classical states of light is determined by orbital and spin decoherence mechanisms, particularly phonon-mediated processes dominant at energy scales up to a few millielectronvolts. Here, we directly measure the spectral function of orbital phonon relaxation in a QDM and benchmark our findings against microscopic kp theory. Our results reveal phonon-mediated relaxation rates exhibiting pronounced resonances and anti-resonances, with rates ranging from several ten ns$^{-1}$ to tens of $\mu$s$^{-1}$. Comparison with a kinetic model reveals the voltage (energy) dependent phonon coupling strength and fully explains the interplay between phonon-assisted relaxation and radiative recombination. These anti-resonances can be leveraged to increase the lifetime of energetically unfavorable charge configurations needed for realizing efficient spin-photon interfaces and multi-dimensional cluster states.

cond-mat.mes-hall↗