Search NASA⌕ Search

SEARCH · Search NASA

Results for “coherency mode transitions”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Incoherent nonadiabatic to coherent adiabatic transition of electron transfer in colloidal quantum dot molecules

Electron transfer is a fundamental process in chemistry, biology, and physics. One of the most intriguing questions concerns the realization of the transitions between nonadiabatic and adiabatic regimes of electron transfer. Using colloidal quantum dot molecules, we computationally demonstrate how the hybridization energy (electronic coupling) can be tuned by changing the neck dimensions and/or the quantum dot sizes. This provides a handle to tune the electron transfer from the incoherent nonadiabatic regime to the coherent adiabatic regime in a single system. We develop an atomistic model to account for several states and couplings to the lattice vibrations and utilize the mean-field mixed quantum-classical method to describe the charge transfer dynamics. Here, we show that charge transfer rates increase by several orders of magnitude as the system is driven to the coherent, adiabatic limit, even at elevated temperatures, and delineate the inter-dot and torsional acoustic modes that couple most strongly to the charge transfer dynamics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Imaging coherent phonons and precursor dynamics in LaFeAsO with 4D ultrafast electron microscopy

In this work, we used 4D ultrafast electron microscopy (UEM) to directly image femtosecond photoinduced structural dynamics in single-crystal LaFeAsO at initial temperatures of 300 and 100 K, above and below the known structural and magnetic phase-transition temperatures, respectively. With nanometer-picosecond resolution, we resolved an initial (precursor) sigmoidlike response arising from photothermal expansion and lattice reorientation that precedes the onset of propagating coherent acoustic phonons (CAPs). In the specific regions probed, the precursor response at 100 K is shorter than at 300 K ($t$ 0.5;100 K = 11.3ps vs $t$ 0.5;300 K = 17.8ps), and the CAP oscillation frequency is lowered with cooling (ƒ CAP;100 K = 12 GHz vs ƒ CAP;300 K = 21 GHz), correlated to known lattice softening due to the structural phase change. The transient CAP behaviors at 300 K are dispersive, displaying an exponentially decaying phase velocity over the first nanosecond. Further, the CAP symmetry at 300 K matches a first-order antisymmetric shear mode (A 1 ), while at 100 K it is best matched by a mostly nondispersive zero-order symmetric mode (S 0 ). These findings illustrate the sensitivity of UEM imaging to spatially heterogeneous dynamics in the Fe-pnictide materials and more broadly in other quantum materials.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Topological nanospaser

We propose a nanospaser made of an achiral plasmonic–metal nanodisk and a two-dimensional chiral gain medium – a monolayer nanoflake of a transition-metal dichalcogenide (TMDC). When one valley of the TMDC is selectively pumped (e.g. by a circular-polarized radiation), the spaser (surface plasmon amplification by stimulated emission of radiation) generates a mode carrying a topological chiral charge that matches that of the gain valley. There is another, chirally mismatched, time-reversed mode with exactly the same frequency but the opposite topological charge; it is actively suppressed by the gain saturation and never generates, leading to a strong topological protection for the generating matched mode. This topological spaser is promising for use in nano-optics and nanospectroscopy in the near field especially in applications to biomolecules that are typically chiral. Another potential application is a chiral nanolabel for biomedical applications emitting in the far field an intense circularly polarized coherent radiation.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Time-Resolved Optical Pump-Resonant X-ray Probe Spectroscopy of 4-Thiouracil: A Simulation Study

We theoretically monitor the photoinduced ππ* → nπ* internal conversion process in 4-thiouracil (4TU), triggered by an optical pump. The element-sensitive spectroscopic signatures are recorded by a resonant X-ray probe tuned to the sulfur, oxygen, or nitrogen K-edge. We employ high-level electronic structure methods optimized for core-excited electronic structure calculation combined with quantum nuclear wavepacket dynamics computed on two relevant nuclear modes, fully accounting for their quantum nature of nuclear motions. We critically discuss the capabilities and limitations of the resonant technique. For sulfur and nitrogen, we document a pre-edge spectral window free from ground-state background and rich with ππ* and nπ* absorption features. The lowest sulfur K-edge shows strong absorption for both ππ* and nπ*. In the lowest nitrogen K-edge window, we resolve a state-specific fingerprint of the ππ* and an approximate timing of the conical intersection via its depletion. A spectral signature of the nπ* transition, not accessible by UV–vis spectroscopy, is identified. The oxygen K-edge is not sensitive to molecular deformations and gives steady transient absorption features without spectral dynamics. Here, the ππ*/nπ* coherence information is masked by more intense contributions from populations. Altogether, element-specific time-resolved resonant X-ray spectroscopy provides a detailed picture of the electronic excited-state dynamics and therefore a sensitive window into the photophysics of thiobases.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2025

Pedestal formation via different trajectories in the stability space in response to the timing scan of neutral beam heating in DIII-D

The frequency of type-I ELMs decreases as the initiation of the neutral beam injection (NBI) heating is delayed with respect to the time when plasma current (I p ) reaches flat-top in the ITER Baseline Scenario discharges in DIII-D. Henceforth, the time gap between the NBI initiation and I p flat-top will be referred to as “heating delay.” As the heating delay is modified, pedestal formation follows different trajectories in the edge current density–pedestal pressure gradient (j edge -∇p e ped ) space from the L-H transition toward the first ELM event. During the stationary phase after the first ELM, the ELM frequency (f ELM ) decreases by a factor of ~2 as the heating delay is increased. A longer pedestal recovery time in the inter-ELM period is observed for the low f ELM discharges as compared to the high f ELM discharges. Both low and high f ELM discharges show nearly identical profiles of electron density and temperature and have a similar MHD stability just before an ELM crash. However, a marked difference is observed in the magnetic spectrogram of the high and low f ELM discharges in response to the variation in the heating delay. The main difference is in the 200–400 kHz range of the magnetic spectra. A quasi-coherent mode (QCM) at 220 kHz and weaker broadband fluctuations are observed in the high f ELM discharges, while only strong broadband fluctuations are prevalent in the low f ELM discharges. ELM-synchronized analysis shows that the time evolution of these modes is different for the high and low f ELM discharges. The localization of both these modes is confirmed at the maximum gradient region of the pedestal. We hypothesize that these modes cause important pedestal transport and that the difference in the pedestal recovery of the high and low f ELM discharges is a result of the difference in transport driven by these modes, as they change with changes in the heating delay. It is demonstrated experimentally for the first time that discharges with similar pedestal parameters can carry the history of the heating delay into the stationary phase and that changes in turbulent-driven transport are a likely cause of changes in f ELM observed with variations of heating delay.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Total internal reflection enabled wide-field coherent anti-Stokes Raman scattering microscopy

Wide-field coherent anti-Stokes Raman scattering (CARS) microscopy offers an attractive means for the rapid and simultaneous acquisition of vibrationally resolved images across a large field of view. A major challenge in the implementation lies in how to achieve sufficiently strong excitation fields necessary to drive the third-order optical responses over the large focal region. Here, we report a new wide-field CARS microscope enabled by a total internal reflection excitation scheme using a femtosecond Ti:Sapphire oscillator to generate pump and broadband near-infrared Stokes pulses. The spectrally broad Stokes pulse, in combination with its inherent chirp, offers not only access to a wide range of Raman modes spanning ${\sim}{1000}$ to ${\sim}{3500}\;{{\rm cm}^{- 1}}$ but also a straightforward means to select vibrational transitions within this range by simply varying the time delay between the pulses. The unique capabilities of this wide-field CARS microscope were validated by acquiring high-quality CARS images from the model and complex biological samples on conventional microscope coverslips.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Total internal reflection enabled wide-field coherent anti-Stokes Raman scattering microscopy

Wide-field coherent anti-Stokes Raman scattering (CARS) microscopy offers an attractive means for the rapid and simultaneous acquisition of vibrationally resolved images across a large field of view. A major challenge in the implementation lies in how to achieve sufficiently strong excitation fields necessary to drive the third-order optical responses over the large focal region. Here, we report a new wide-field CARS microscope enabled by a total internal reflection excitation scheme using a femtosecond Ti:Sapphire oscillator to generate pump and broadband near-infrared Stokes pulses. The spectrally broad Stokes pulse, in combination with its inherent chirp, offers not only access to a wide range of Raman modes spanning ∼ <#comment/> 1000 to ∼ <#comment/> 3500 c m − <#comment/> 1 but also a straightforward means to select vibrational transitions within this range by simply varying the time delay between the pulses. The unique capabilities of this wide-field CARS microscope were validated by acquiring high-quality CARS images from the model and complex biological samples on conventional microscope coverslips.

Doughty, Benjamin (ORCID:0000000164299329)↗
NASA NTRS2016

Overview of LBTI: A Multipurpose Facility for High Spatial Resolution Observations

The Large Binocular Telescope Interferometer (LBTI) is a high spatial resolution instrument developed for coherent imaging and nulling interferometry using the 14.4 m baseline of the 2x8.4 m LBT. The unique telescope design, comprising of the dual apertures on a common elevation-azimuth mount, enables a broad use of observing modes. The full system is comprised of dual adaptive optics systems, a near-infrared phasing camera, a 1-5 micrometer camera (called LMIRCam), and an 8-13 micrometer camera (called NOMIC). The key program for LBTI is the Hunt for Observable Signatures of Terrestrial planetary Systems (HOSTS), a survey using nulling interferometry to constrain the typical brightness from exozodiacal dust around nearby stars. Additional observations focus on the detection and characterization of giant planets in the thermal infrared, high spatial resolution imaging of complex scenes such as Jupiter's moon, Io, planets forming in transition disks, and the structure of active Galactic Nuclei (AGN). Several instrumental upgrades are currently underway to improve and expand the capabilities of LBTI. These include: Improving the performance and limiting magnitude of the parallel adaptive optics systems; quadrupling the field of view of LMIRcam (increasing to 20"x20"); adding an integral field spectrometry mode; and implementing a new algorithm for path length correction that accounts for dispersion due to atmospheric water vapor. We present the current architecture and performance of LBTI, as well as an overview of the upgrades.

The Large Binocular Telescope Interferometer (LBTI↗
DOE OSTI2024

Deciphering between enhanced light emission and absorption in multi-mode porphyrin cavity polariton samples

Abstract It remains unclear how the collective strong coupling of cavity-confined photons to the electronic transitions of molecular chromophore leverages the distinct properties of the polaritonic constituents for future technologies. In this study, we design, fabricate, and characterize multiple types of Fabry-Pérot (FP) mirco-resonators containing copper(II) tetraphenyl porphyrin (CuTPP) to show how cavity polariton formation affects radiative relaxation processes in the presence of substantial non-Condon vibronic coupling between two of this molecule’s excited electronic states. Unlike the prototypical enhancement of Q state radiative relaxation of CuTPP in a FP resonator incapable of forming polaritons, we find the light emission processes in multimode cavity polariton samples become enhanced for cavity-exciton energy differences near those of vibrations known to mediate non-Condon vibronic coupling. We propose the value of this detuning is consistent with radiative relaxation of Herzberg-Teller polaritons into collective molecular states coupled to the cavity photon coherently. We contrast the feature stemming from light emission from the HT polariton state with those that occur due to polariton-enhanced light absorption. Our results demonstrate the landscape of molecular and photonic interactions enabled by cavity polariton formation using complex chromophores and how researchers can design resonators to leverage these interactions to characterize and control polaritonic properties.

Odewale, Elizabeth O.↗
DOE OSTI2022

Topological edge modes without symmetry in quasiperiodically driven spin chains

Here we construct an example of a 1d quasiperiodically driven spin chain whose edge states can coherently store quantum information, protected by a combination of localization, dynamics, and topology. In a sharp departure from topological phases in static and periodically driven (Floquet) spin chains, this model does not rely upon microscopic symmetry protection: Instead, the edge states are protected purely by emergent dynamical symmetries. We explore the dynamical signatures of this emergent dynamical symmetry-protected topological (EDSPT) order through exact numerics, time evolving block decimation, and analytic high-frequency expansion, finding evidence that the EDSPT is a stable dynamical phase protected by bulk many-body localization up to (at least) stretched-exponentially long timescales, and possibly beyond. We argue that EDSPTs are special to the quasiperiodically driven setting, and cannot arise in Floquet systems. Moreover, we find evidence of a type of boundary critical with no known static or Floquet analogue, in which the edge spin dynamics transition from quasiperiodic to chaotic, leading to bulk thermalization.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Overview of ASDEX upgrade results in view of ITER and DEMO

Experiments on ASDEX Upgrade (AUG) in 2021 and 2022 have addressed a number of critical issues for ITER and EU DEMO. A major objective of the AUG programme is to shed light on the underlying physics of confinement, stability, and plasma exhaust in order to allow reliable extrapolation of results obtained on present day machines to these reactor-grade devices. Concerning pedestal physics, the mitigation of edge localised modes (ELMs) using resonant magnetic perturbations (RMPs) was found to be consistent with a reduction of the linear peeling-ballooning stability threshold due to the helical deformation of the plasma. Conversely, ELM suppression by RMPs is ascribed to an increased pedestal transport that keeps the plasma away from this boundary. Candidates for this increased transport are locally enhanced turbulence and a locked magnetic island in the pedestal. The enhanced D-alpha (EDA) and quasi-continuous exhaust (QCE) regimes have been established as promising ELM-free scenarios. Here, the pressure gradient at the foot of the H-mode pedestal is reduced by a quasi-coherent mode, consistent with violation of the high-n ballooning mode stability limit there. This is suggestive that the EDA and QCE regimes have a common underlying physics origin. In the area of transport physics, full radius models for both L- and H-modes have been developed. These models predict energy confinement in AUG better than the commonly used global scaling laws, representing a large step towards the goal of predictive capability. A new momentum transport analysis framework has been developed that provides access to the intrinsic torque in the plasma core. In the field of exhaust, the X-Point Radiator (XPR), a cold and dense plasma region on closed flux surfaces close to the X-point, was described by an analytical model that provides an understanding of its formation as well as its stability, i.e., the conditions under which it transitions into a deleterious MARFE with the potential to result in a disruptive termination. With the XPR close to the divertor target, a new detached divertor concept, the compact radiative divertor, was developed. Here, the exhaust power is radiated before reaching the target, allowing close proximity of the X-point to the target. No limitations by the shallow field line angle due to the large flux expansion were observed, and sufficient compression of neutral density was demonstrated. With respect to the pumping of non-recycling impurities, the divertor enrichment was found to mainly depend on the ionisation energy of the impurity under consideration. In the area of MHD physics, analysis of the hot plasma core motion in sawtooth crashes showed good agreement with nonlinear 2-fluid simulations. This indicates that the fast reconnection observed in these events is adequately described including the pressure gradient and the electron inertia in the parallel Ohm’s law. Concerning disruption physics, a shattered pellet injection system was installed in collaboration with the ITER International Organisation. Thanks to the ability to vary the shard size distribution independently of the injection velocity, as well as its impurity admixture, it was possible to tailor the current quench rate, which is an important requirement for future large devices such as ITER. Progress was also made modelling the force reduction of VDEs induced by massive gas injection on AUG. The H-mode density limit was characterised in terms of safe operational space with a newly developed active feedback control method that allowed the stability boundary to be probed several times within a single discharge without inducing a disruptive termination. Regarding integrated operation scenarios, the role of density peaking in the confinement of the ITER baseline scenario (high plasma current) was clarified. The usual energy confinement scaling ITER98(p,y) does not capture this effect, but the more recent H20 scaling does, highlighting again the importance of developing adequate physics based models. Advanced tokamak scenarios, aiming at large non-inductive current fraction due to non-standard profiles of the safety factor in combination with high normalised plasma pressure were studied with a focus on their access conditions. A method to guide the approach of the targeted safety factor profiles was developed, and the conditions for achieving good confinement were clarified. Based on this, two types of advanced scenarios (‘hybrid’ and ‘elevated’

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2026

Quantum nanophotonic interface for tin-vacancy centers in thin-film diamond

The negatively charged tin-vacancy center in diamond (SnV − ) is an excellent solid state qubit with optically-addressable transitions and a long electron spin coherence time at elevated (∼1.7 K). However, implementing scalable quantum nodes with high-fidelity optical readout of the electron spin state requires efficient photon emission and collection from the system. Here, in this manuscript, we report a quantum photonic interface for SnV−centers based on one-dimensional photonic crystal cavities fabricated in diamond thin films. Furthermore, we provide a rigorous description of the spontaneous emission dynamics of our system, taking into account individual contributions from both the C and D transitions of the emitter. This allows for determination of Purcell factors per transition and, by extension, the C/D branching ratio SnV− zero phonon line. We observe quality factors up to ~6000 across this sample, and measure up to a 12-fold lifetime reduction, which translates into a Purcell factor of 𝐹 𝐶 =26.2±1.5 for a targeted C transition. By considering the cavity mode polarization alignment with the C and D transition dipole moments, we validate the C/D branching ratio to be 𝜂 BR =0.75±0.01, in line with previous theoretical and experimental findings.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Edge radiated temperature fluctuations across confinement regime transitions in favorable and unfavorable drift configurations at ASDEX Upgrade

Abstract The physics behind the difference in heating power threshold for the low to high confinement (L–H) transition between favorable ion B × ∇ B drift (toward active X -point) and unfavorable ion B × ∇ B drift (away from active X -point) magnetic configurations is a longstanding open question. In this work we show differences in edge ( ρ p o l = 0.95 –1.0) turbulence in matched heating power favorable and unfavorable magnetic configuration discharges using a correlation electron cyclotron emission diagnostic to measure radiated temperature ( T r a d ) fluctuations. During power matched L-mode phases, the edge T r a d fluctuations have higher amplitude in the unfavorable configuration plasma as compared to the favorable configuration plasma. The lower fluctuation amplitude in favorable configuration is observed concomitant with increased E × B shear, as compared to the unfavorable case. Although this turbulence is different in amplitude, it is similar in radial and frequency structure between favorable and unfavorable configurations and grows to the weakly coherent mode during the I-mode phase of the unfavorable configuration discharge. A broadband pedestal fluctuation is seen during an inter-ELM H-mode period of the favorable configuration discharge.

Physics↗
DOE OSTI2023

Terahertz-Driven Local Dipolar Correlation in a Quantum Paraelectric

Light-induced ferroelectricity in quantum paraelectrics is a new avenue of achieving dynamic stabilization of hidden orders in quantum materials. In this Letter, we explore the possibility of driving a transient ferroelectric phase in the quantum paraelectric KTaO 3 via intense terahertz excitation of the soft mode. We observe a long-lived relaxation in the terahertz-driven second harmonic generation (SHG) signal that lasts up to 20 ps at 10 K, which may be attributed to light-induced ferroelectricity. Through analyzing the terahertz-induced coherent soft-mode oscillation and finding its hardening with fluence well described by a single-well potential, we demonstrate that intense terahertz pulses up to 500 kV=cm cannot drive a global ferroelectric phase in KTaO 3 . Instead, we find the unusual long-lived relaxation of the SHG signal comes from a terahertz-driven moderate dipolar correlation between the defect-induced local polar structures. We discuss the impact of our findings on current investigations of the terahertz-induced ferroelectric phase in quantum paraelectrics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Zonally dominated dynamics and Dimits threshold in curvature-driven ITG turbulence

The saturated state of turbulence driven by the ion-temperature-gradient instability is investigated using a two-dimensional long-wavelength fluid model that describes the perturbed electrostatic potential and perturbed ion temperature in a magnetic field with constant curvature (a $Z$ -pinch) and an equilibrium temperature gradient. Numerical simulations reveal a well-defined transition between a finite-amplitude saturated state dominated by strong zonal-flow and zonal temperature perturbations, and a blow-up state that fails to saturate on a box-independent scale. We argue that this transition is equivalent to the Dimits transition from a low-transport to a high-transport state seen in gyrokinetic numerical simulations (Dimits et al. , Phys. Plasmas , vol. 7, 2000, 969). A quasi-static staircase-like structure of the temperature gradient intertwined with zonal flows, which have patch-wise constant shear, emerges near the Dimits threshold. The turbulent heat flux in the low-collisionality near-marginal state is dominated by turbulent bursts, triggered by coherent long-lived structures closely resembling those found in gyrokinetic simulations with imposed equilibrium flow shear (van Wyk et al. , J. Plasma Phys. , vol. 82, 2016, 905820609). The breakup of the low-transport Dimits regime is linked to a competition between the two different sources of poloidal momentum in the system – the Reynolds stress and the advection of the diamagnetic flow by the $\boldsymbol {E}\times \boldsymbol {B}$ flow. By analysing the linear ion-temperature-gradient modes, we obtain a semi-analytic model for the Dimits threshold at large collisionality.

Physics↗
DOE OSTI2019

Three-dimensional phase evolution and stress-induced non-uniform Li intercalation behavior in lithium iron phosphate

A lithium iron phosphate (LiFePO 4 ) olivine cathode displays rich phase transition behavior during charging/discharging. Despite extensive studies, the evolution of the LiFePO 4 /FePO 4 two-phase coexistence structure and the underlying mechanism are still a point of debate due to the intricate and often disparate phase morphologies observed. Here we apply phase-field simulations to provide detailed insights into the three-dimensional phase evolution process in LiFePO 4 upon delithiation under a large driving force. The simulation reveals that the coherency stress arising from the LiFePO 4 /FePO 4 lattice mismatch destabilizes the initially flat delithiation front and induces filamentary growth of the FePO 4 phase along [010], which is in excellent agreement with a recent operando X-ray imaging study. The combined simulation and experimental results provide the first illustration of the phenomenon of stress-induced instability of the lithium (de)intercalation front in battery electrode compounds. We show that this phenomenon is facilitated by the surface mode of coherent spinodal decomposition in LiFePO 4 and influenced by the anisotropies of misfit strain, elasticity and lithium diffusion. It is detrimental to battery performance and life by causing stress concentration and reducing the lithium (de)intercalation kinetics and thus should be mitigated.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
NASA NTRS1986

Theoretical studies of Resonance Enhanced Stimulated Raman Scattering (RESRS) of frequency doubled Alexandrite laser wavelengths in cesium vapor

This work focused on understanding the effects of arbitrary transverse and longitudinal relaxation rates on the susceptibilities of coherently driven three-level systems. The approximation of a single relaxation rate often made in previous work is strongly invalidated by the variation in the spontaneous emission lifetime between various atomic level pairs in systems such as cesium. It is of great importance to the problem of nonlinear infrared generation to determine the dependence of both real and imaginary susceptibility on relaxation rates. The imaginary susceptibility on the pump transition determines the absorption of pump photons and the imaginary susceptibility on the laser transition determines the spectral dependence of the gain. This is of particular importance for pure Raman emission (i.e., absorption at linecenter of the gain transition) as it determines the tunability characteristics we are aiming to predict. The real susceptibility is important when cavities are used at the signal field as this will determine the loaded resonance of the Raman oscillator. Researchers show that in some cases which result from having different relaxation rates mode splitting may result, allowing more than one frequency to have the same Raman wavelength, possibly resulting in a temporal instability.

Lawandy, N. M.↗
DOE OSTI2025

Slow Electron Spin Relaxation at Ambient Temperatures with Copper Coordinated by a Rigid Macrocyclic Ligand

Paramagnetic transition metal complexes can serve as quantum bits, storing phase information through unpaired electrons. Despite their promise, these systems often require low temperatures and tend to rapidly decohere. Recent efforts have sought to improve longitudinal relaxation (T 1 ), which provides an upper limit for phase coherence (T m ), by investigating existing literature compounds with reduced vibrational coupling and orbital angular momentum. However, synthetic strategies for improving T 1 through novel ligand design have remained scant. Here, we disclose the synthesis of a new modular macrocyclic ligand framework with four nitrogen donors (N 4 ) derived from phenanthroline that supports room-temperature coherent Cu(II) spin centers. The optimized complex more than doubles the T 1 over the next best Cu(II)-N 4 compound and exhibits a room temperature coherence time (T m ) of 0.28 μs, close to previously reported values. This performance enhancement arises from a tight binding site with short Cu–N distances, resulting in a stronger ligand field and reduced thermal accessibility of symmetric vibrational modes. This work demonstrates a practical approach to enabling spin coherence at room temperature, a factor critical to accessing relevant quantum bits and biological sensors, through a designer macrocyclic ligand platform.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗