Spin Coherence Lifetime Research Articles

The contribution of methyl groups to electron spin decoherence of nitroxides in glassy matrices.

Long electron spin coherence lifetimes are crucial for high sensitivity and resolution in many pulse electron paramagnetic resonance (EPR) experiments aimed at measuring hyperfine and dipolar couplings, as well as in potential quantum sensing applications of molecular spin qubits. In immobilized systems, methyl groups contribute significantly to electron spin decoherence as a result of methyl torsional quantum tunneling. We examine the electron spin decoherence dynamics of the nitroxide radical 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) in both a methyl-free solvent and a methyl-containing solvent at cryogenic temperature. We model nitroxide and solvent methyl effects on decoherence using cluster correlation expansion (CCE) simulations extended to include methyl tunneling and compare the calculations to experimental data. We show that by using the methyl tunneling frequency as a fit parameter, experimental Hahn echo decays can be reproduced fairly well, allowing structural properties to be investigated in silico. In addition, we examine the Hahn echo of a hypothetical system with an unpaired electron and a single methyl to determine the effect of geometric configuration on methyl-driven electron spin decoherence. The simulations show that a methyl group contributes the most to electron spin decoherence if it is located between 2.5 and 6-7Å from the electron spin, with its orientation being of secondary importance.

All-in-one quantum diamond microscope for sensor characterization

Ensembles of nitrogen-vacancy (NV) centers in diamond are a leading platform for sensing and imaging magnetic fields at room temperature, in part due to advances in diamond growth. An essential step to improving diamond material involves the characterization of crystal and NV-related properties, such as strain and paramagnetic impurities, which can shift and broaden the NV resonances used for sensing. Full sample characterization through wide-field imaging enables both fast and detailed feedback for growers, along with the estimation of sensing performance before use. We present a quantum diamond microscope tailored for millimeter-scale wide-field mapping of key quantum properties of NV-diamond chips, including NV ensemble photoluminescence intensity, spin-lattice relaxation time (T1), and spin-coherence lifetimes (T2 and T2*). Our design also allows for lattice stress/strain and birefringence magnitude/angle mapping, and their in situ correlation with NV properties.

Purcell Enhancement and Spin Spectroscopy of Silicon Vacancy Centers in Silicon Carbide Using an Ultrasmall Mode-Volume Plasmonic Cavity.

Silicon vacancy (VSi) centers in 4H-silicon carbide have emerged as a strong candidate for quantum networking applications due to their robust electronic and optical properties, including a long spin coherence lifetime and bright, stable emission. Here, we report the integration of VSi centers with a plasmonic nanocavity to Purcell enhance the emission, which is critical for scalable quantum networking. Employing a simple fabrication process, we demonstrate plasmonic cavities that support a nanoscale mode volume and exhibit an increase in the spontaneous emission rate with a measured Purcell factor of up to 48. In addition to investigating the optical resonance modes, we demonstrate an improvement in the optical stability of the spin-preserving resonant optical transitions relative to the radiation-limited value. The results highlight the potential of nanophotonic structures for advancing quantum networking technologies and emphasize the importance of optimizing emitter-cavity interactions for efficient quantum photonic applications.

Tunable Quantum Coherence of Luminescent Molecular Spins Organized via Block Copolymer Self‐Assembly

AbstractElectronic or nuclear spins represent promising candidates of qubits for applications in quantum information technologies and spintronic devices. However, it remains a challenge to achieve scalable and spatially defined organization of a large number of spins as qubits, which is essential in the feasible fabrication of quantum circuits. We report a strategy of block copolymer self‐assembly to organize molecular spins as qubits across molecular to micro‐/nano‐scales in polymeric films of organic luminescent radicals centered in star‐like block copolymers. We have achieved not only scalable and spatially defined organization of the molecular spins in polymeric films with long‐range periodic ordering but also controllable spin‐lattice relaxation dynamics and spin coherence lifetimes that can be finely tuned by the domain sizes and rigidities of the polymeric matrices.

Long Spin Coherence Times on C59N-C60 Heterodimer Radicals Entrapped in Cycloparaphenylene Rings

We investigate the effect of introducing C60 to (C59N)2 and the molecular ring, [10]cycloparaphenylene ([10]CPP), using electron paramagnetic resonance (EPR) measurements supported by density functional theory (DFT) calculations. Incorporating C60 into the system results in the formation of novel stable [10]CPP ⊃ C59N-C60• ⊂ [10]CPP encapsulated heterodimer radicals whose spin is localized on C60 and manifests in EPR measurements as a signal at g = 2.0022 without any discernable hyperfine structure. This signal has an exceptionally long spin coherence lifetime of 440 μs at room temperature, far longer than any of the radical fullerene species reported in the literature and over twice that of the C59N• ⊂ [10]CPP radical. The radicals are long-lived, with EPR signal still strong over a year after thermal activation. The [10]CPP ⊃ C59N-C60• ⊂ [10]CPP oligomer is more stable than C59N• ⊂ [10]CPP radicals and becomes the predominant species at room temperature after annealing. Its formation is thermally activated with an experimental activation energy of only 0.189 eV, as compared to 0.485 eV for the pure azafullerene-[10]CPP case. The [10]CPP ⊃ C59N-C60• ⊂ [10]CPP radicals discovered here could be used to bridge C59N• ⊂ [10]CPPs acting as qubits, providing effective coupling between them.

Excitonic Spin-Coherence Lifetimes in CdSe Nanoplatelets Increase Significantly with Core/Shell Morphology.

We report spin-polarized transient absorption for colloidal CdSe nanoplatelets as functions of thickness (2-6 monolayer thickness) and core/shell motif. Using electro-optical modulation of co- and cross-polarization pump-probe combinations, we sensitively observe spin-polarized transitions. Core-only nanoplatelets exhibit few-picosecond spin lifetimes that weakly increase with layer thickness. The spectral content of differenced spin-polarized signals indicate biexciton binding energies that decrease with increasing thickness and smaller values than previously reported. Shell growth of CdS with controlled thicknesses, which partially delocalize the electron from the hole, significantly increases the spin lifetime to ∼49 ps at room temperature. Implementation of ZnS shells, which do not alter delocalization but do alter surface termination, increased spin lifetimes up to ∼100 ps, bolstering the interpretation that surface termination heavily influences spin coherence, likely due to passivation of dangling bonds. Spin precession in magnetic fields both confirms long coherence lifetime at room temperature and yields the excitonic g factor.

Monte Carlo simulation of the nuclear spin decoherence process in Eu3+ : Y2SiO5 crystals

${\mathrm{Eu}}^{3+}$:${\mathrm{Y}}_{2}{\mathrm{SiO}}_{5}$ crystals are promising candidates for quantum memories because their nuclear spin coherence lifetime can be extended to 47 seconds at a particular magnetic field. Although an extended coherence lifetime of 6 hours can be achieved with a large number of dynamic decoupling sequences, these pulses will also introduce unwanted noise. To realize quantum storage with a lifetime of hours, it is necessary to quantitatively characterize the spin decoherence process of ${\mathrm{Eu}}^{3+}$ ions to guide the experimental efforts. In practice, a number of limiting factors could impose a limit on the achievable spin coherence lifetime, which includes the spin inhomogeneous broadening of the ${\mathrm{Eu}}^{3+}$ ensemble and the homogeneity and stability of the external magnetic field. Here, we provide a Monte Carlo simulation model of the nuclear spin decoherence process of ${\mathrm{Eu}}^{3+}$ ions in ${\mathrm{Y}}_{2}{\mathrm{SiO}}_{5}$ crystals, and these limiting factors are considered to provide an accurate prediction of the spin coherence lifetimes. This method is universal and can be applied to other rare-earth-ion-doped crystals.

Spin Dynamics of a Solid-State Qubit in Proximity to a Superconductor.

A broad effort is underway to understand and harness the interaction between superconductors and spin-active color centers with an eye on hybrid quantum devices and novel imaging modalities of superconducting materials. Most work, however, overlooks the interplay between either system and the environment created by the color center host. Here we use a diamond scanning probe to investigate the spin dynamics of a single nitrogen-vacancy (NV) center proximal to a superconducting film. We find that the presence of the superconductor increases the NV spin coherence lifetime, a phenomenon we tentatively rationalize as a change in the electric noise due to a superconductor-induced redistribution of charge carriers near induced redistribution of charge carriers near the NV. We then build on these findings to demonstrate transverse-relaxation-time-weighted imaging of the superconductor film. These results shed light on the dynamics governing the spin coherence of shallow NVs, and promise opportunities for new forms of noise spectroscopy and imaging of superconductors.

Coherent spin dynamics of rare-earth doped crystals in the high-cooperativity regime

Rare-earth doped crystals have long coherence times and the potential to provide quantum interfaces between microwave and optical photons. Such applications benefit from a high cooperativity between the spin ensemble and a microwave cavity---this motivates an increase in the rare-earth ion concentration which in turn impacts the spin coherence lifetime. We measure spin dynamics of two rare-earth spin species, $^{145}\mathrm{Nd}$ and Yb, doped into ${\mathrm{Y}}_{\text{2}}{\mathrm{SiO}}_{\text{5}}$, coupled to a planar microwave resonator in the high-cooperativity regime, in the temperature range $1.2\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ to $14\phantom{\rule{0.16em}{0ex}}\mathrm{mK}$. We identify relevant decoherence mechanisms, including instantaneous diffusion arising from resonant spins and temperature-dependent spectral diffusion from impurity electron and nuclear spins in the environment. We explore two methods to mitigate the effects of spectral diffusion in the Yb system in the low-temperature limit, first, using magnetic fields of up to 1 T to suppress impurity spin dynamics and, second, using transitions with low effective $g$ factors to reduce sensitivity to such dynamics. Finally, we demonstrate how the ``clock transition'' present in the $^{171}\mathrm{Yb}$ system at zero field can be used to increase coherence times up to ${T}_{2}=6(1)\phantom{\rule{0.16em}{0ex}}\mathrm{ms}$.

Mechanism of Electron Spin Decoherence in a Partially Deuterated Glassy Matrix.

Long electron spin coherence lifetimes are essential for applications in quantum information science and electron paramagnetic resonance, for instance, for nanoscale distance measurements in biomolecular systems using double electron-electron resonance. We experimentally investigate the decoherence dynamics under the Hahn echo sequence of the organic radical d18-TEMPO in a variably deuterated frozen water:glycerol matrix. The coherence time (phase memory time) TM scales with proton concentration as [1H]-0.65. For selectively deuterated matrices, decoherence is accelerated in the presence of proton clustering, that is, substantial short-range density in the proton-proton radial distribution functions (<3 Å). Simulations using molecular dynamics and many-body spin quantum dynamics show excellent agreement with experiment and show that geminal proton pairs such as CH2 and OH2 groups are major decoherence drivers. This provides a predictive tool for designing molecular systems with long electron spin coherence times.

Photon echo, spectral hole burning, and optically detected magnetic resonance inYb3+171:LiNbO3bulk crystal and waveguides

Recent progress in the realization of high-quality optical resonators and waveguides along with the possibility to incorporate rare-earth ions, make lithium niobate a promising material to build integrated platforms for quantum information processing. $^{171}\mathrm{Yb}^{3+}$ is a particularly attractive system because it can show long coherence lifetimes at zero magnetic field thanks to transitions insensitive to magnetic field fluctuations. In this paper, we investigate the optical and spin properties of $^{171}\mathrm{Yb}^{3+}$ ions in ${\mathrm{LiNbO}}_{3}$ bulk crystals as well as implanted waveguides. Using hole-burning spectroscopy and optically detected magnetic resonance, we studied ground and excited state hyperfine structures and probed optical and spin spectral holes. Importantly, the hole linewidths suggest that part of the ions in the waveguides are in a similar environment as in the bulk sample. We furthermore characterized spin population relaxation and coherence lifetimes of $^{171}\mathrm{Yb}^{3+}$ ions in the bulk crystal at temperatures between 50 mK and 9 K. At low temperatures, ${T}_{2}$ up to 9.5 $\ensuremath{\mu}\mathrm{s}$ (34 kHz homogeneous linewidth) and spin relaxation rates as long as $\ensuremath{\approx}100$ ms were measured. Our results show that $^{171}\mathrm{Yb}^{3+}$:$\mathrm{Li}\mathrm{Nb}{\mathrm{O}}_{3}$ is a system that exhibits narrow optical homogeneous linewidths over a 50 GHz bandwidth together with an electron spin degree of freedom. This is of interest for a variety of applications in integrated quantum photonics such as quantum memories or quantum processors.

Optical and spin inhomogeneous linewidths in 171Yb[formula omitted]:Y[formula omitted]SiO5

Single crystals of 171Yb3+:Y2SiO5 are promising systems for quantum technologies as an efficient optical to spin interface. This is due to the long optical and spin coherence lifetimes, or narrow homogeneous linewidths, observed in this material at zero magnetic field. Inhomogeneous linewidths are also of importance since they affect peak absorption, available bandwidth or spin–spin interactions. In this work, we investigate inhomogeneous linewidths in a series of 171Yb3+:Y2SiO5 single crystals grown by the Czochralski method with the purpose of identifying the broadening mechanisms in the regime of ultra-low doping, i.e. in the ppm range. In a series of samples obtained with varying doping level, growth atmosphere, and cut at different locations in a crystal boule, optical inhomogeneous linewidths between 0.6 and 1.3 GHz are observed. This study suggests that these variations are due to changes in dislocation densities. Spin inhomogeneous linewidths, recorded using electron paramagnetic resonance, did not show the differences between samples observed in the optical domain. They were otherwise found to vary as a function of magnetic field orientation, enabling determination of directions that minimize e.g. detrimental spin–spin interactions. These results suggest ways to reduce optical inhomogeneous linewidths in 171Yb3+:Y2SiO5, which is of interest for high efficiency quantum memories and optical to microwave quantum transducers.

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Rare earth ions are actively investigated as optically addressable spin systems for quantum technologies thanks to their long optical and spin coherence lifetimes. 171Yb3+, which has 1/2 electron and nuclear spins, recently raised interest for its simple hyperfine structure that moreover can result in long coherence lifetimes at zero magnetic field, an unusual property for paramagnetic rare earth ions. Here, we report on the optical inhomogeneous and homogeneous linewidths in 171Yb3+:Y2SiO5 (site 2) for different doping concentrations. While inhomogeneous linewidth is not correlated to 171Yb3+ concentration, the homogeneous one strongly decreases between 10 and 2 ppm doping level, reaching 255 Hz at 3 K. This is attributed to a slowing down of 171Yb3+ ground state spin flip-flops.

Однородные и неоднородные ширины линий в оптических спектрах кристалла Y-=SUB=-2-=/SUB=-SiO-=SUB=-5-=/SUB=- : -=SUP=-171-=/SUP=-Yb-=SUP=-3+-=/SUP=-

Rare earth ions are actively investigated as optically addressable spin systems for quantum technologies thanks to their long optical and spin coherence lifetimes. 171Yb3+, which has 1/2 electron and nuclear spins, recently raised interest for its simple hyperfine structure that moreover can result in long coherence lifetimes at zero magnetic field, an unusual property for paramagnetic rare earth ions. Here, we report on the optical inhomogeneous and homogeneous linewidths in 171Yb3+:Y2SiO5 (site 2) for different doping concentrations. While inhomogeneous linewidth is not correlated to 171Yb3+ concentration, the homogeneous one strongly decreases between 10 and 2 ppm doping level, reaching 255 Hz at 3 K. This is attributed to a slowing down of 171Yb3+ ground state spin flip-flops.

Photoredox-Mediated Sensitization of Lanthanide Dopants by Perovskite Nanocrystals

Trivalent lanthanide ions (Ln3+) have electronically isolated f-orbitals that support excited states, which, due to their ultra-narrow emission and long spin coherence lifetimes, are potentially suitable as hosts for spin qubits. These excited states must however be generated through photosensitization due to the low-absorption cross sections of Ln3+. This paper describes the mechanism of photosensitization of Yb3+ and Sm3+ ions by their CsPbCl3 perovskite nanocrystal (NC) host matrices, through examination of the photophysical processes in NCs doped with seven different Ln3+ ions. An observed dependence of the NC’s band-edge photoluminescence (PL) on the potential of the Ln3+/Ln2+ redox couple implies the presence of a charge transfer intermediate in the sensitization mechanism. Ultrafast transient absorption (TA) experiments indicate that (i) a previously identified Ln3+-Cl–-VPb2–-Cl–-Ln3+ defect is formed within 1 ps of photoexcitation of the NC regardless of the yield of photosensitization, (ii) the first step of photosensitization, an electron transfer, occurs in 10s of picoseconds, and (iii) the resulting charge-separated state forms the emissive species, Ln3+*, through a slower subsequent hole transfer from the NC. A mechanistic understanding of Ln3+ dopant sensitization provides a framework for choosing the right combination of host matrix and Ln3+ species for efficient photosensitization.

A Magic Angle Spinning Activated 17O DNP Raser.

In the raser effect, a sample spontaneously emits continuous radiofrequency radiation, allowing exceptionally narrow NMR line widths to be recorded without applying pulses. To achieve this phenomenon, a large negative magnetization must be induced, which we show here can be achieved for the 17O magnetization of isotopically labeled Gd-doped CeO2 using solid effect dynamic nuclear polarization (DNP), at high field and 110 K. This allows a 2 mHz line width to be measured, which is limited only by the magnetic field stability. The raser effect can be reversibly activated and deactivated by magic angle spinning (MAS), which modulates the nuclear spin coherence lifetime. The use of MAS DNP to enable the raser effect should be further applicable to other systems and nuclei.

A Frequency-Multiplexed Coherent Electro-optic Memory in Rare Earth Doped Nanoparticles.

Quantum memories for light are essential components in quantum technologies like long-distance quantum communication and distributed quantum computing. Recent studies have shown that long optical and spin coherence lifetimes can be observed in rare earth doped nanoparticles, opening exciting possibilities over bulk materials, e.g., for enhancing coupling to light and other quantum systems, and material design. Here, we report on coherent light storage in Eu3+:Y2O3 nanoparticles using the Stark echo modulation memory (SEMM) quantum protocol. We first measure a nearly constant Stark coefficient of 50 kHz/(V/cm) across a bandwidth of 15 GHz, which is promising for broadband operation. Storage of light is then demonstrated with an effective coherence lifetime of 5 μs. Pulses with two different frequencies are also stored, confirming frequency-multiplexing capability, and are used to demonstrate the memory high phase fidelity. These results open the way to nanoscale optical quantum memories with increased efficiency, bandwidth, and processing capabilities.

A calibration method for coil constants using an atomic spin self-sustaining vector magnetometer

The self-sustaining atomic magnetometer has the advantage of high sensitivity and long spin coherence lifetime, based on which we demonstrate a novel method to calibrate the magnetic coil constants precisely. Via non-destructive phase measurement and coherent optical pumping, the spin polarization of rubidium atoms is regenerated coherently and the Larmor precession signal is oscillating continuously. In this stable state, the calibrating capability is achieved by applying current to coils and scan the magnetic components along x- and y-direction. The magnetic field magnitude is obtained from precession frequency and the coil constants can be derived from the fitting equation directly. The constants of coils in the experiment are 246.010 ± 0.034 nT/mA and 197.452 ± 0.025 nT/mA in the x- and y-directions, respectively.

Quantized charge transport driven by a surface acoustic wave in induced unipolar and bipolar junctions

Surface acoustic waves (SAWs) have been used to transport single electrons across long distances of several hundreds of microns. They can potentially be instrumental in the implementation of scalable quantum processors and quantum repeaters, by facilitating interaction between distant qubits. While most of the work thus far has focused on SAW devices in doped GaAs/AlGaAs heterostructures, we have developed a method of creating lateral p-n junctions in an undoped heterostructure containing a quantum well, with the expected advantages of having reduced charge noise and increased spin-coherence lifetimes due to the lack of dopant scattering centres. We present experimental observations of SAW-driven single-electron quantised current in an undoped GaAs/AlGaAs heterostructure, where single electrons were transported between regions of induced electrons. We also demonstrate pumping of electrons by a SAW across the sub-micron depleted channel between regions of electrons and holes, and observe light emission at such a lateral p-n junction. Improving the lateral confinement in the junction should make it possible to produce a quantised electron-to-hole current and hence SAW-driven emission of single photons.

Electromagnetic 0.1-100 kHz noise does not disrupt orientation in a night-migrating songbird implying a spin coherence lifetime of less than 10 µs.

According to the currently prevailing theory, the magnetic compass sense in night-migrating birds relies on a light-dependent radical-pair-based mechanism. It has been shown that radio waves at megahertz frequencies disrupt magnetic orientation in migratory birds, providing evidence for a quantum-mechanical origin of the magnetic compass. Still, many crucial properties, e.g. the lifetime of the proposed magnetically sensitive radical pair, remain unknown. The current study aims to estimate the spin coherence time of the radical pair, based on the behavioural responses of migratory birds to broadband electromagnetic fields covering the frequency band 0.1-100 kHz. A finding that the birds were unable to use their magnetic compass under these conditions would imply surprisingly long-lived (greater than 10 µs) spin coherence. However, we observed no effect of 0.1-100 kHz radiofrequency (RF) fields on the orientation of night-migratory Eurasian blackcaps (Sylvia atricapilla). This suggests that the lifetime of the spin coherence involved in magnetoreception is shorter than the period of the highest frequency RF fields used in this experiment (i.e. approx. 10 µs). This result, in combination with an earlier study showing that 20-450 kHz electromagnetic fields disrupt magnetic compass orientation, suggests that the spin coherence lifetime of the magnetically sensitive radical pair is in the range 2-10 µs.