Average Quantum Research Articles

The effects of physical form, moisture, humic acids, and mixtures on the photolysis of insensitive munitions compounds

The explosive formulations IMX-101 and IMX-104 are replacing conventional explosives in munitions, making them safer to transport and handle. However, munitions manufacturing and military training can lead to the environmental release of constituent insensitive munitions compounds (IMCs) such as 2,4-dinitroanisole (DNAN), 3-nitro-1,2,4-triazol-5-one (NTO), and nitroguanidine (NQ). These IMCs absorb ultraviolet light and transform photochemically into products with potentially greater toxicity. This study explores the effects of physical form, moisture, humic acids, and compound mixtures on the photolysis of solid and dissolved IMCs under UV-A (350 nm) and UV-B (300 nm) light. Irradiation of dry vs. moist solid IMC crystals yielded few measured products, and while photolysis rates were not significantly different, they were orders of magnitude slower than for aqueous IMCs. There was no significant difference in photolysis rates for aqueous IMCs irradiated with 0, 0.4, and 4 mg L-1 humic acids, but 40 and 400 mg L-1 humic acids inhibited NTO and enhanced NQ photolysis. In two- and three-component aqueous mixtures, DNAN photolysis was enhanced by NQ (at 300 and 350 nm) and NTO (at 350 nm); NTO photolysis was inhibited by DNAN and enhanced by NQ (both at 300 nm); and NQ photolysis was inhibited by both DNAN and NTO (both at 300 and 350 nm). The average quantum yields of the IMCs irradiated alone in solution were: 8.29 × 10–5 (300 nm) and 6.26 × 10–5 (350 nm) for DNAN; 5.76 × 10–4 (300 nm) and 1.74 × 10–4 (350 nm) for NTO; and 1.01 × 10–2 (300 nm) and 1.14 × 10–4 (350 nm) for NQ. Although organic and inorganic products were detected in the mixtures, an average of 15–35 % of the theoretical starting IMC masses (as nitrogen) was not accounted for. Overall, aqueous IMCs transformed 4–48 times faster than the solid IMCs, but the environmentally-relevant conditions tested were found to play a minor role in IMC photolysis.

Excitation wavelength and time dependent colour tunable room temperature phosphorescence from boron doped carbon nanodots.

Developing metal free room temperature phosphorescence (RTP) materials have received tremendous attention due its potential application in various fields such as sensing, optoelectronics and anticounterfeiting. Herein, we have synthesized an excitation wavelength and time dependent phosphorescent boron doped carbon nanodots (BCNDs) by thermal treatment of ethanolamine and boric acid at 240°C, where boric acid act as both doping and host agents. The obtained BCNDs display blue to orange fluorescence in both aqueous medium and solid state. In addition, the BCNDs display tunable orange-yellow-green phosphorescence in solid state under UV and visible light, lasting upto 10s, visible to naked eye. The boron and nitrogen doping regulates the band gap of the BCNDs, resulting the phosphorescence colour tunability. The average phosphorescence lifetime and quantum yield of BCNDs are found to be 1.27s and 8.61% respectively. Based on the optical properties, the BCNDs are applied as security ink in information encryption and security marking. Hence, this work can promote the development of metal free phosphorescent carbon based materials which may find application in various emerging fields.

Kinetic modelling of ozonation and photolytic ozonation of metronidazole removal from water

This work addresses the ozonation, photolysis, and photolytic ozonation of metronidazole (MTZ), a widely used antibiotic frequently detected in urban wastewater. A UVA source emitting radiation between 300 and 400 nm was utilized. The presence of scavengers such as t-butanol and sodium azide confirmed the role of hydroxyl radicals in both ozonation and photolysis processes. Conversely, singlet oxygen did not influence the photolytic processes. The average quantum yields of MTZ and ozone were determined to be 1.2 × 10−3 and 0.72 mol/Einstein, respectively, for the 300–400 nm wavelength range. In direct MTZ photolysis, a stoichiometric ratio of 0.34 mol of hydroxyl radicals formed per mol of photolyzed MTZ was observed. However, the effects of hydroxyl radicals on the MTZ photolytic rate were only significant after 45 min of reaction time. Using rate constant data from literature and quantum yields calculated in this study, a kinetic model for both MTZ ozonation and photolytic ozonation was proposed, enabling the prediction of MTZ conversion and degradation rates. This model includes three intermediate compounds that also consume ozone and hydroxyl radicals. The results show that experimental and calculated concentrations of MTZ are within an error margin of less than 14 % in all cases.

Quantum-Secured Data Centre Interconnect in a field environment

In the evolving landscape of quantum technology, the increasing prominence of quantum computing poses a significant threat to the security of conventional public key infrastructure. Quantum key distribution (QKD), an established quantum technology at a high readiness level, emerges as a viable solution with commercial adoption potential. QKD facilitates the establishment of secure symmetric random bit strings between two geographically separated, trustworthy entities, safeguarding communications from potential eavesdropping. In particular, data centre interconnects can leverage the potential of QKD devices to ensure the secure transmission of critical and sensitive information in preserving the confidentiality, security, and integrity of their stored data. In this article, we present the successful implementation of a QKD field trial within a commercial data centre environment that utilises the existing fibre network infrastructure. The achieved average secret key rate of 2.392 kbps and an average quantum bit error rate of less than 2% demonstrate the commercial feasibility of QKD in real-world scenarios. As a use case study, we demonstrate the secure transfer of files between two data centres through the Quantum-Secured Virtual Private Network, utilising secret keys generated by the QKD devices. %This demonstration marks a significant milestone in the deployment of QKD across Singapore, establishing a foundation for widespread adoption and enhancing the infrastructure for practical, quantum-safe communication in commercial environments.

Enhanced Photon Recycling Enables Efficient Perovskite Light‐Emitting Diodes

AbstractPerovskite light‐emitting diodes (PeLEDs) have recently experienced rapid growth in performance. While photon recycling, which involves the reemission of reabsorbed light, significantly boosts efficiency, PeLED structures are typically based on classical design principles, often overlooking photon recycling. Here, a practical strategy to maximize the benefit of the photon recycling effect in PeLEDs is demonstrated. Parasitic absorption in electrodes represents a significant loss that impedes the efficient recycling of photons in trapped modes. The design strategy is verified by improving the average electroluminescence quantum efficiencies from 19.5% to 22.0% in near‐infrared PeLEDs with thinner indium tin oxide (ITO) electrodes, ultimately achieving a champion efficiency of 23.9%. The effect of photon recycling is visualized by transient photoluminescence mapping. It is quantified computationally that the additional efficiency coming from photon recycling is doubled from 2.3% to 4.8% in the device by suppressing the relative loss in ITO from 39% to 13%. The strategies raise the theoretical upper bound efficiency of PeLEDs with a gold top electrode from 27% to 37% by boosting the photon recycling effect.

Enhancing the Overall Performance of Perovskite Solar Cells with a Nano-Pyramid Anti-Reflective Layer

Perovskite solar cells (PSCs) still suffer from varying degrees of optical and electrical losses. To enhance the light decoupling and capture ability of Planar PSCs, an ultra-thin PSC structure with an Al2O3 pyramid anti-reflection layer (Al2O3 PARL) is proposed. The effect of the structure of the Al2O3 PARL on the photoelectric performance of PSCs was investigated by changing various parameters. Under the AM1.5 solar spectrum (300–800 nm), the average light absorption rates and quantum efficiency (QE) of PSCs containing pyramid-array textured rear layers (PARLs) were significantly higher than those of planar PSCs. The Al2O3 PARL-based PSCs achieved a light absorption rate of 96.05%. Additionally, electrical simulations were performed using the finite element method (FEM) to calculate the short-circuit current density (JSC), open-circuit voltage (VOC), and maximum power (Pmax). Based on the maximum value of the average light absorbance, the geometric structure of the Al2O3 pyramid PSCs was optimized, and the optimization results coincided with the JSC and QE results. The results of the electrical simulation indicated that the maximum JSC was 23.54 mA/cm2. Additionally, the JSC of the Al2O3 pyramid PSCs was 22.73% higher than that of planar PSCs, resulting in a photoelectric conversion efficiency (PCE) of 24.34%. As a result, the photoelectric conversion rate of the solar cells increased from 14.01% to 17.19%. These findings suggest that the presence of the Al2O3 PARL enhanced photon absorption, leading to an increase in electron–hole pairs and ultimately improving the photocurrent of the solar cells.

Constructing magnetically propelled piezoelectric and pyroelectric bifunctional micromotors to boost the photocatalytic H2 production involving biomass reforming

Biomass-assisted photocatalytic water splitting for hydrogen (H2) production has attracted widespread interest, which is important for the development of green H2 energy and the high value-added utilization of biomass. Although photothermal utilization can improve solar energy conversion efficiency, the elevated temperature also enhances the likelihood of electron-hole collisions. Herein, magnetically propelled PVDF/Fe3O4@g-C3N4 spiral micromotors were constructed to easily foster the synergistic coupling of piezoelectric and pyroelectric effects, which is beneficial to enhance the directional migration of photogenerated carriers at high temperatures. With both piezo- and pyroelectric effects, the biomass glucose involved H2 production rate on PVDF/Fe3O4@g-C3N4 spiral micromotors is 42.3 μmol/h, representing a significant increase of 31.9 times compared to water splitting without these effects, and the average apparent quantum yield at ordinary pressure can reach 12.6 %. Furthermore, photoluminescence and variable-temperature electrochemistry demonstrate that the piezo-pyroelectric coupling can accelerate the separation of carriers. Meanwhile, COMSOL simulations and KPFM tests show that the built-in electric field of the sample is enhanced under the piezo-pyroelectric effect. The spiral micromotors can easily realize the synergism of piezoelectric and pyroelectric effects, which provides an effective strategy to enhance the built-in electric field and thereby improve the performance of photocatalytic H2 evolution involving biomass reforming.

Raman Sideband Cooling of Molecules in an Optical Tweezer Array to the 3D Motional Ground State

Ultracold polar molecules are promising for quantum information processing and searches for physics beyond the standard model. Laser cooling to ultracold temperatures is an established technique for trapped diatomic and triatomic molecules. Further cooling of the molecules to near the motional ground state is crucial for reducing various dephasings in quantum and precision applications. In this work, we demonstrate Raman sideband cooling (RSC) of CaF molecules in optical tweezers to near their motional ground state, with average motional occupation quantum numbers of n¯x=0.16(12), n¯y=0.17(17) (radial directions), and n¯z=0.22(16) (axial direction), and a 3-D motional-ground-state probability of 54±18% of the molecules that survive the RSC. This process paves the way to increase molecular coherence times in optical tweezers for robust quantum computation and simulation applications. Published by the American Physical Society 2024

Raman amplifier based on stimulated Raman scattering in a methane-filled hollow core fiber

This article reports on a single pass amplifier based on stimulated Raman scattering in a methane-filled negative curvature hollow core fiber (HCF) to transition 1.06 μm power to 1.54 μm. The researchers measured the highest average Raman power at a single frequency in a methane filled HCF to date of 4.92 W (246 μJ/pulse), with a high average quantum efficiency of 95.9%. A numerical model for the system was developed and shows good agreement with measured thresholds and efficiencies. Model results from a trade space study indicate configuration regimes necessary to maximize 1.54 μm power while avoiding power loss from the secondary shift.

High-rate intercity quantum key distribution with a semiconductor single-photon source

Quantum key distribution (QKD) enables the transmission of information that is secure against general attacks by eavesdroppers. The use of on-demand quantum light sources in QKD protocols is expected to help improve security and maximum tolerable loss. Semiconductor quantum dots (QDs) are a promising building block for quantum communication applications because of the deterministic emission of single photons with high brightness and low multiphoton contribution. Here we report on the first intercity QKD experiment using a bright deterministic single photon source. A BB84 protocol based on polarisation encoding is realised using the high-rate single photons in the telecommunication C-band emitted from a semiconductor QD embedded in a circular Bragg grating structure. Utilising the 79 km long link with 25.49 dB loss (equivalent to 130 km for the direct-connected optical fibre) between the German cities of Hannover and Braunschweig, a record-high secret key bits per pulse of 4.8 × 10−5 with an average quantum bit error ratio of ~ 0.65% are demonstrated. An asymptotic maximum tolerable loss of 28.11 dB is found, corresponding to a length of 144 km of standard telecommunication fibre. Deterministic semiconductor sources therefore challenge state-of-the-art QKD protocols and have the potential to excel in measurement device independent protocols and quantum repeater applications.

Paper Scintillator Incorporated with Scintillator-Silica Fine Powders: Photophysical Characterization and Proof of Concept Demonstration of Tritium Detection.

In order to decrease the generation of radioactive waste, it is of interest to develop a scintillator capable of absorbing tritiated solutions for efficient detection of low-energy β-particles from tritium. In this work, paper scintillator incorporated with scintillator-silica fine powders (FPs), which is composed of scintillator-silica nanoparticles (NPs) attached to silica FP, was fabricated and evaluated. The scintillator-silica NPs contained liquid scintillators benzoic acid, 2,5-diphenyloxazole (PPO), and 1,4-bis(5-phenyloxazol-2-yl) benzene (POPOP). Photophysical characterization was executed by means of photoluminescence, fluorescence lifetime, quantum efficiency, and radioluminescence under X-ray excitation. POPOP emission was confirmed by absorbing the emissions from benzoic acid and PPO. Radioluminescence results confirmed POPOP emission. Fluorescence lifetime analysis yielded a 1.29 ± 0.01 ns main fast decay (64.2%) combined with a 4.00 ± 0.04 ns slower decay (35.8%). The combined luminescence results suggested that most POPOP in the paper scintillator was solvated. At 301 nm, the average quantum efficiency from both faces of the paper scintillator was about 4%, and at 370 nm, it was about 11%. The paper scintillator detected 3H β-particles by dipping the paper scintillator into tritiated water without a liquid scintillator. The counting efficiency depended on water content in the paper scintillator, and it increased to above 10% for tritium activity less than 200 dpm since it was preferentially adsorbed by vapor pressure isotopic effect and isotopic exchanged tritium on the surface of the scintillator-silica FP in the paper scintillator.

Solar overall water-splitting by a spin-hybrid all-organic semiconductor

Direct solar-to-hydrogen conversion from pure water using all-organic heterogeneous catalysts remains elusive. The challenges are twofold: (i) full-band low-frequent photons in the solar spectrum cannot be harnessed into a unified S1 excited state for water-splitting based on the common Kasha-allowed S0 → S1 excitation; (ii) the H+ → H2 evolution suffers the high overpotential on pristine organic surfaces. Here, we report an organic molecular crystal nanobelt through the self-assembly of spin-one open-shell perylene diimide diradical anions (:PDI2-) and their tautomeric spin-zero closed-shell quinoid isomers (PDI2-). The self-assembled :PDI2-/PDI2- crystal nanobelt alters the spin-dependent excitation evolution, leading to spin-allowed S0S1 → 1(TT) → T1 + T1 singlet fission under visible-light (420 nm~700 nm) and a spin-forbidden S0 → T1 transition under near-infrared (700 nm~1100 nm) within spin-hybrid chromophores. With a triplet-triplet annihilation upconversion, a newly formed S1 excited state on the diradical-quinoid hybrid induces the H+ reduction through a favorable hydrophilic diradical-mediated electron transfer, which enables simultaneous H2 and O2 production from pure water with an average apparent quantum yield over 1.5% under the visible to near-infrared solar spectrum.

Novel sunlight-induced monochloramine activation system for efficient microcontaminant abatement

As an eco-friendly and sustainable energy, solar energy has great application potential in water treatment. Herein, simulated sunlight was for the first time utilized to activate monochloramine for the degradation of environmental organic microcontaminants. Various microcontaminants could be efficiently degraded in the simulated sunlight/monochloramine system. The average innate quantum yield of monochloramine over the wavelength range of simulated sunlight was determined to be 0.068 mol/Einstein. With the determined quantum yield, a kinetic model was established. Based on the good agreement between the simulated and measured photolysis and radical contributions to the degradation of ibuprofen and carbamazepine, the major mechanism of monochloramine activation by simulated sunlight was proposed. Chlorine radical (Cl∙) and hydroxyl radical (HO∙) were major radicals responsible for microcontaminant degradation in the system. Moreover, the model facilitated a deep investigation into the effects of different reaction conditions (pH, monochloramine concentration, and water matrix components) on the degradation of ibuprofen and carbamazepine, as well as the roles of the involved radicals. The differences between simulated and measured degradation data of each microcontaminant under all conditions were less than 10 %, indicating the strong reliability of the model. The model could also make good prediction for microcontaminant degradation in the natural sunlight/monochloramine system. Furthermore, the formation of disinfection byproducts (DBPs) was evaluated at different oxidation time in simulated sunlight/monochloramine with and without post-chloramination treatment. In real waters, organic components showed more pronounced suppression on microcontaminant degradation efficiency than inorganic ions. This study provided a systematic investigation into the novel sunlight-induced monochloramine activation system for efficient microcontaminant degradation, and demonstrated the potential of the system in practical applications.

Spiro[fluorene-9,9′-xanthene]-based hole transporting materials modulated by mono- and bis- benzodioxino[2,3-b]pyrazine pendant groups for perovskite QLEDs

In this work, we designed and synthesized two new hole-transporting materials with a nonplanar three-dimensional (3D) conformation. They were achieved by incorporating spiro[fluorene-9,9′-xanthene] as a cross-shaped configuration scaffold and adding either mono- (H1) or bis- benzodioxino[2,3-b]pyrazine (H2) pyrazine as pendant groups. Both compounds exhibit remarkable thermal stability, with thermal decomposition temperature (Td) of 462 (H1) and 504 °C (H2), respectively. Moreover, the structural substitution with benzodioxino[2,3-b]pyrazine units successfully aligned the energy levels of both materials with the perovskite quantum dot luminescence layer. Hereby, the fabricated perovskite QLEDs using H1 as hole-transporting materials (HTMs) featured an excellent average external quantum efficiency (EQE) of up to 9.5% with a maximum luminance of 22368 cd m−2, which is much higher than that of the H2-based devices with an EQE of 6.6% under the same conditions. The excellent device performance from H1 can be attributed to its asymmetric structure by the introduction of monosubstituted benzodioxino[2,3-b]pyrazine groups, as evidenced by its high hole mobility of 1.90 × 10−4 cm2 V−1 s−1 and improved interface interaction with adjunct layers. Thus, this design approach may bring a fresh perspective to the utilization of solution-processable small-molecule HTMs in high-performance Pe-QLEDs and other optoelectronics in the future.

Classes of Gaussian states for squeezing estimation

This study explores a detailed examination of various classes of single- and two-mode Gaussian states as key elements for an estimation process, specifically targeting the evaluation of an unknown squeezing parameter encoded in one mode. To quantify the efficacy of each probe, we employ the concept of Average Quantum Fisher Information (AvQFI) as a robust metric to quantify the optimal performance associated with specific classes of Gaussian states as input. For single-mode probes, we identify pure squeezed single-mode states as the optimal choice and we explore the correlation between Coherence and AvQFI. Also, we show that pure two-mode squeezed states exhibit behavior resembling their single-mode counterparts for estimating the encoded squeezing parameter, and we studied the interplay between entanglement and AvQFI. This paper presents both analytical and numerical results that encompass all the studied classes, offering valuable insights for quantum estimation processes.

Electron spin-states reconfiguration induced by alternating temperature gradient for boosting photocatalytic hydrogen evolution on hollow core-shell FeS2/CuCo2O4 Z-scheme heterostructure

The pyroelectric effect and electron spin-state reconfiguration play a critical role in photocatalysis but are seldom investigated. This work is the first to exploit the fluctuating temperature (ΔT) between the cold-hot alternation in photocatalysis to drive the pyroelectric effect and electron spin-sate reconfiguration. FeS2/CuCo2O4 (FS/CCO) hollow core-shell heterojunctions were prepared using hydrothermal and heating treatment methods. The FeS2 (FS) can generate heat under near-infrared (NIR) light to provide the elevated temperature end required for the pyroelectric effect of CuCo2O4 (CCO) under the influence of ΔT. With this thermoelectric and pyroelectric effect, CCO can release surface charges, generating spontaneous polarization, changing the electron (eg) filling number on Co surface sites, reversing the spin electron state, thus controlling the carriers' migration direction and enhancing their separation and migration rate, and finally prolonging their lifetime. As a result, the as-designed FS/CCO-15 composites yielded up to 19.5 mmol g−1 h−1 extraordinary photocatalytic performance, i.e., 10.2 and 6.45-fold of the pure FS (1.92 mmol g−1 h−1) and CCO (3.02 mmol g−1h−1) under simulated sunlight, respectively. It also yielded up to 19.8% average apparent quantum yield. This work thoroughly explored the distinctive impact of the pyroelectric effect, electron spin-state reconfiguration, orbital coupling effect, and hydrogen evolution, guiding us and creating more possibilities for photocatalytic technology and efficiency using NIR light.

Organic inorganic hybrid solar cell with photoactive hole transporting CuSbS2 nanoflakes

An easy-to-process, low-cost and environmentally benign organic inorganic hybrid solar cell (HSC) based on textured silicon (t-Si) is fabricated. The heterojunction solid state cell is composed of n-type t-Si having a micro-pyramidal surface with good anti-reflection properties, coated with a p-type layer of CuSbS2 nanoflakes dispersed in a polymer matrix of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). The large hole density (2.7 × 1015 /cm3), high photoconductivity (5.37 mS cm−1), mono-dispersity of nanoflakes (50–80 nm), increased recombination resistance and a broad band absorption, with a band gap of ∼ 0.85 eV render CuSbS2 nanoflakes to be an ideal photo-absorber cum hole transport material for a highly scalable all solid-state HSC. Besides these attributes, the thermodynamically aligned energy levels of t-Si and CuSbS2 nanoflakes enable one-directional pathways for transfer and transport of electrons and holes to their respective contacts, yielding a high-power conversion efficiency (PCE) of 8.5 % under AM 1.5, 1 sun irradiance along with an average external quantum efficiency of 60 % superior by 39.2 % relative to its analogue devoid of CuSbS2. The effect of alkali texturization on the photovoltaic performance of the cells is also delineated by comparison with planar (pl)-Si based cells. The long-term stability of the In-Ga/t-Si/PEDOT:PSS + CuSbS2/Ag cell under intermittent illumination and storage over eight weeks confirmed from the nominal drop in PCE by ∼ 22 % demonstrates the efficacy of this affordable wet-chemistry approach for developing robust Si based HSC contrasting with the classical and expensive inorganic p-n junction crystalline Si solar cell.

Slow dynamics for self-adjoint semigroups and unitary evolution groups

We obtain slow dynamics for self-adjoint semigroups and unitary evolution groups. For semigroups, the slow dynamics is for orbits, and for the average (quantum) return probability in the case of unitary evolution groups. We present an application to the quantum dynamics of purely absolutely continuous systems.

Convergent photophysiology and prokaryotic assemblage structure in epilithic cyanobacterial tufts and algal turf communities.

As global change spurs shifts in benthic community composition on coral reefs globally, a better understanding of the defining taxonomic and functional features that differentiate proliferating benthic taxa is needed to predict functional trajectories of reef degradation better. This is especially critical for algal groups, which feature dramatically on changing reefs. Limited attention has been given to characterizing the features that differentiate tufting epilithic cyanobacterial communities from ubiquitous turf algal assemblages. Here, we integrated an insitu assessment of photosynthetic yield with metabarcoding and shotgun metagenomic sequencing to explore photophysiology and prokaryotic assemblage structure within epilithic tufting benthic cyanobacterial communities and epilithic algal turf communities. Significant differences were not detected in the average quantum yield. However, variability in yield was significantly higher in cyanobacterial tufts. Neither prokaryotic assemblage diversity nor structure significantly differed between these functional groups. The sampled cyanobacterial tufts, predominantly built by Okeania sp., were co-dominated by members of the Proteobacteria, Firmicutes, and Bacteroidota, as were turf algal communities. Few detected ASVs were significantly differentially abundant between functional groups and consisted exclusively of taxa belonging to the phyla Proteobacteria and Firmicutes. Assessment of the distribution of recovered cyanobacterial amplicons demonstrated that alongside sample-specific cyanobacterial diversification, the dominant cyanobacterial members were conserved across tufting cyanobacterial and turf algal communities. Overall, these data suggest a convergence in taxonomic identity and mean photosynthetic potential between tufting epilithic cyanobacterial communities and algal turf communities, with numerous implications for consumer-resource dynamics on future reefs and trajectories of reef functional ecology.

Measurement-induced multipartite-entanglement regimes in collective spin systems

We study the competing effects of collective generalized measurements and interaction-induced scrambling in the dynamics of an ensemble of spin-1/2 particles at the level of quantum trajectories. This setup can be considered as analogous to the one leading to measurement-induced transitions in quantum circuits. We show that the interplay between collective unitary dynamics and measurements leads to three regimes of the average Quantum Fisher Information (QFI), which is a witness of multipartite entanglement, as a function of the monitoring strength. While both weak and strong measurements lead to extensive QFI density (i.e., individual quantum trajectories yield states displaying Heisenberg scaling), an intermediate regime of classical-like states emerges for all system sizes where the measurement effectively competes with the scrambling dynamics and precludes the development of quantum correlations, leading to sub-Heisenberg-limited states. We characterize these regimes and the crossovers between them using numerical and analytical tools, and discuss the connections between our findings, entanglement phases in monitored many-body systems, and the quantum-to-classical transition.