arXiv subjects

Amir Hen

Publications and source records attributed to Amir Hen.

8 recordsLinked to original sources

arXiv2026

Signatures of Spin Coherence in Chiral Coupled Quantum Dots

Chiral-induced spin selectivity (CISS) enables spin selectivity of charge carriers in chiral molecular systems without magnetic materials. While spin selectivity has been widely investigated, its quantum coherence has not yet been explored. Here, we investigate spin-dependent photoluminescence (PL) dynamics in multilayer quantum-dot (QD) assemblies coupled by chiral linkers. Using circularly polarized excitation in the presence of an external magnetic field, we observe a pronounced modulation of the PL lifetime that depends on the magnetic field magnitude and geometry. The lifetime difference between left- and right-circularly polarized excitations exhibits a field-angle dependence, consistent with spin precession driven by the transverse magnetic-field component relative to the chiral axis. A model incorporating coupled spin precession and decay processes reproduces the experimental trends. These results establish chiral QD assemblies as a room-temperature platform for probing quantum coherent manifestations of the CISS effect, with implications for spintronic and quantum technologies.

quant-ph↗

arXiv2025

Spin and Orbital Magnetism in UH2 Thin Films Studied by X-ray Magnetic Circular Dichroism

Uranium dihydride UH2 is a metastable phase unknown in bulk form but accessible through thin-film synthesis. We prepared UH2 films by reactive dc sputtering on CaF2(001) or Si(001) substrates, the latter equipped with a Mo buffer layer to suppress a U-Si interdiffusion. On CaF2, UH2 adopts the fluorite-type structure with a near-[1 1 1] out-of-plane texture, four rotational domains, and a lattice parameter a = 539 +- 3 pm without measurable strain, whereas the Mo-buffered film is polycrystalline. X-ray photoelectron spectroscopy confirmed complete hydrogenation and minimal oxidation. Magnetization and XMCD measurements show ferromagnetic ordering with Curie temperatures of 120-130 K and a uranium 5f moment of 0.9 {\mu}B/U, dominated by the orbital contribution ({\mu}L ~ 1.4 {\mu}B, {\mu}S ~ -0.5 {\mu}B), in a good agreement with GGA+U computations, which otherwise overestimate absolute values of the spin and orbital components. The slightly reduced moment in thinner CaF2-supported films is attributed to surface U(IV) species. These results demonstrate that thin-film synthesis enables stabilization of UH2 and direct probing of 5f magnetism, opening pathways toward higher uranium hydrides and interface-engineered actinide systems.

cond-mat.mtrl-sci↗

arXiv2025

Quantum Co-Magnetometer Using Diamond Nitrogen-Vacancy Centers and Rubidium Cells

Recent advances in chip scale magnetic quantum sensing have produced platforms that pair unprecedented sensitivity with extreme miniaturization. Here, we demonstrate a hybrid quantum sensor by combining Nitrogen-Vacancy (NV) centers in diamond with a rubidium (Rb) vapor cell, designed for precise magnetic field measurements and quantum exploration. The hybrid comagnetometer leverages the high resolution vector magnetic sensing of NV centers along with the high scalar field sensitivity of the Rb vapor, enhancing the estimation of the magnetic field in terms of magnitude, direction and spatial distribution. A micromachined mm scale vapor cell containing Rb atoms is paired with a bulk diamond, enabling optical and microwave control of both quantum systems for integrated field estimation. Simulations and experimental results confirm the improved accuracy of the system in magnetic field measurements, demonstrating a beyond 10 dB improvement. This NV and Rb platform offers a versatile route toward portable, sensitive magnetometry and opens new possibilities for integrated, multi-modal quantum sensing.

quant-ph↗

arXiv2025

Quantum Imaging of Ferromagnetic van der Waals Magnetic Domain Structures at Ambient Conditions

Recently discovered 2D van der Waals magnetic materials, and specifically Iron-Germanium-Telluride ($\rm Fe_{5}GeTe_{2}$), have attracted significant attention both from a fundamental perspective and for potential applications. Key open questions concern their domain structure and magnetic phase transition temperature as a function of sample thickness and external field, as well as implications for integration into devices such as magnetic memories and logic. Here we address key questions using a nitrogen-vacancy center based quantum magnetic microscope, enabling direct imaging of the magnetization of $\rm Fe_{5}GeTe_{2}$ at sub-micron spatial resolution as a function of temperature, magnetic field, and thickness. We employ spatially resolved measures, including magnetization variance and cross-correlation, and find a significant spread in transition temperature yet with no clear dependence on thickness down to 15 nm. We also identify previously unknown stripe features in the optical as well as magnetic images, which we attribute to modulations of the constituting elements during crystal synthesis and subsequent oxidation. Our results suggest that the magnetic anisotropy in this material does not play a crucial role in their magnetic properties, leading to a magnetic phase transition of $\rm Fe_{5}GeTe_{2}$ which is largely thickness-independent down to 15 nm. Our findings could be significant in designing future spintronic devices, magnetic memories and logic with 2D van der Waals magnetic materials.

cond-mat.mtrl-sci↗

arXiv2025

Correlation-induced phase shifts and time delays in resonance enhanced high harmonic generation from Cr+

We investigate resonance-enhanced high harmonic generation (rHHG) in Cr+ by comparing a 1D shape-resonant model, time-dependent density functional theory (TDDFT), and independent particle approximation (IPA) simulations. Previous studies linked rHHG to the 3p -> 3d giant resonance, suggesting a modified four-step model where recolliding electrons are first captured in the autoionizing state before recombining into the ground state, potentially leading to an emission delay associated with the resonance lifetime. While both the 1D-model and TDDFT reproduce experimental spectra, TDDFT reveals that rHHG counterintuitively originates from spin-down 3p states, while spin-up 3d electrons negligibly contribute. The IPA fails to reproduce rHHG, highlighting the significance of electron correlations. Furthermore, TDDFT revealed a correlation induced ~480 attosecond time delay, accompanied by a strong phase shift across the resonance, potentially explaining earlier RABBIT measurements. Our work sheds light on long-standing open questions in rHHG and should advance novel ultrafast spectroscopies of electron correlations and resonances.

physics.atom-ph↗

arXiv2024

Realization of robust quantum noise characterization in the presence of coherent errors

Complex quantum systems and their various applications are susceptible to noise of coherent and incoherent nature. Characterization of noise and its sources is an open, key challenge in quantum technology applications, especially in terms of distinguishing between inherent incoherent noise and systematic coherent errors. In this paper, we study a scheme of repeated sequential measurements that enables the characterization of incoherent errors by reducing the effects of coherent errors. We demonstrate this approach using a coherently controlled Nitrogen Vacancy in diamond, coupled to both a natural nuclear spin bath (non-Markovian) and to experimentally controlled relaxation through an optical pumping process (nearly Markovian). Our results show mitigation of coherent errors both for Markovian and Non-Markovian incoherent noise profiles. We apply this scheme to the estimation of the dephasing time ($T_2^*$) due to incoherent noise. We observe an improved robustness against coherent errors in the estimation of dephasing time ($T_2^*$) compared to the standard (Ramsey) measurement.

quant-ph↗

arXiv2023

Modified Split Ring Resonators for Efficient and Homogeneous Microwave Control of Large Volume Spin Ensembles

Quantum sensing using local defects in solid-state systems has gained significant attention over the past several years, with impressive results demonstrated both in Academia and in Industry. Specifically, employing large volume and high density ensembles for beyond state-of-the-art sensitives is of clear interest. A major obstacle for achieving such record sensitivities is associated with the need to realize strong, homogeneous driving of the sensor defects. Here we focus on high-frequency microwave sensing using nitrogen-vacancy centers in diamond, and develop a modified split-ring resonator design to address this issue. We demonstrate enhanced drive strengths and homogeneities over large volumes compared to previous results, with prospects for enabling the desired sensitivities. We reach Rabi frequencies of up to 18 [MHz] with an efficiency ratio of 2 [$Gauss/\sqrt{Watt}$], along with an inhomogeneity of $<0.7\%$ in a volume of $0.1\:mm^3$.

quant-ph↗

arXiv2018

Probing Magnetic Sublattices in Multiferroic Ho$_{0.5}$Nd$_{0.5}$Fe$_{3}$(BO$_{3}$)$_{4}$ Single Crystal using X-ray Magnetic Circular Dichroism

Using element-specific X-ray magnetic circular dichroism (XMCD) technique we have studied different magnetic sublattices in a multiferroic Ho$_{0.5}$Nd$_{0.5}$Fe$_{3}$(BO$_{3}$)$_{4}$ single crystal. The XMCD measurements at the \emph{L}$_{2,3}$-edges of Ho and Nd, and at the Fe \emph{K}-edge have been performed at \emph{T}=2~K under a magnetic field up to 17~T applied along the trigonal \emph{c}-axis as well as in the basal \emph{ab}-plane. All three magnetic sublattices are shown to undergo a spin-reorientation transition under magnetic field applied along the \emph{c}-axis. On the contrary, when magnetic field is applied in the \emph{ab}-plane only the holmium atoms exhibit a magnetization jump. Thus, the element-specific magnetization curves revealed the Ho sublattice to be much stronger coupled to the Fe one than the Nd sublattice. The results demonstrate that the Ho$^{3+}$ subsystem plays even more dominant role in magnetic behavior of Ho$_{0.5}$Nd$_{0.5}$Fe$_{3}$(BO$_{3}$)$_{4}$ crystal than in pure HoFe$_{3}$(BO$_{3}$)$_{4}$ crystal.

cond-mat.mtrl-sci↗