arXiv subjects

Sven Bodenstedt

Publications and source records attributed to Sven Bodenstedt.

8 recordsLinked to original sources

arXiv2026

Experimental demonstration of finite-size general security via discrete-modulated CVQKD with real time postprocessing

Continuous-variable quantum key distribution (CVQKD) is compatible with telecommunication infrastructure, but implementing composable security with experimentally practical resources has remained challenging, particularly for discrete-modulated (DM) protocols. We report the first experimental demonstration of a DM CVQKD system that generates composable secret keys against general attacks with finite-size block lengths on the order of $\sim 10^{6}$ rounds via a quadrature phase shift keying (QPSK) system. Our implementation follows a variable-length, general security framework enabled by modern entropy accumulation techniques and conic optimization, whose experimental pipeline allows real-time operation on near-commercial hardware.

quant-ph↗

arXiv2026

Local, mm-scale $^1$H magnetic resonance imaging using atomic vapors

We demonstrate a practical and sensitive low-field approach to magnetic resonance imaging (MRI) of $μ$L-scale samples using an optically pumped magnetometer (OPM). Using a simple setup where a commercial OPM is placed directly adjacent to a sample, without intermediary signal-pickup coils, we perform one- and two-dimensional imaging with a >1 cm field of view and sub-mm Fourier-limited resolution at 10 $μ$T, near Earth's field. This enables (i) high-throughput, low-field MRI of fluidic and tissue samples, and (ii) a quantitative benchmark of the sensitive volume surrounding the OPM.

physics.chem-ph↗

arXiv2023

Real-time polarimetry of hyperpolarized $^{13}$C nuclear spins using an atomic magnetometer

We introduce a method for non-destructive quantification of nuclear spin polarization, of relevance to hyperpolarized spin tracers widely used in magnetic resonance from spectroscopy to in vivo imaging. In a bias field of around 30 nT we use a high-sensitivity miniaturized $^{87}$Rb vapor magnetometer to measure the field generated by the sample, as it is driven by a windowed dynamical decoupling pulse sequence that both maximizes the nuclear spin lifetime and modulates the polarization for easy detection. We demonstrate the procedure applied to a 0.08 M hyperpolarized [1--$^{13}$C]-pyruvate solution produced by dissolution dynamic nuclear polarization, measuring polarization repeatedly during natural decay at Earth's field. Application to real-time quality monitoring of hyperpolarized substances is discussed.

physics.chem-ph↗

arXiv2022

Miniature biplanar coils for alkali-metal-vapor magnetometry

Atomic spin sensors offer precision measurements using compact, microfabricated packages, placing them in a competitive position for both market and research applications. Performance of these sensors such as dynamic range may be enhanced through magnetic field control. In this work, we discuss the design of miniature coils for three-dimensional, localized field control by direct placement around the sensor, as a flexible and compact alternative to global approaches used previously. Coils are designed on biplanar surfaces using a stream-function approach and then fabricated using standard printed-circuit techniques. Application to a laboratory-scale optically pumped magnetometer of sensitivity approximately 20 fT/Hz$^{1/2}$ is shown. We also demonstrate the performance of a coil set measuring $7 \times 17 \times 17$ mm$^3$ that is optimized specifically for magnetoencephalography, where multiple sensors are operated in proximity to one another. Characterization of the field profile using $^{87}$Rb free-induction spectroscopy and other techniques show $>$96% field homogeneity over the target volume of a MEMS vapor cell and a compact stray field contour of approximately 1% at 20 mm from the center of the cell.

physics.atom-ph↗

arXiv2022

Meridional composite pulses for low-field magnetic resonance

We discuss procedures for error-tolerant spin control in environments that permit transient, large-angle reorientation of magnetic bias field. Short sequences of pulsed, non-resonant magnetic field pulses in a laboratory-frame meridional plane are derived. These are shown to have band-pass excitation properties comparable to established amplitude-modulated, resonant pulses used in high, static-field magnetic resonance. Using these meridional pulses, we demonstrate robust $z$ inversion in proton ($^{1}$H) nuclear magnetic resonance near earth's field.

physics.chem-ph↗

arXiv2021

Decoupling of Spin Decoherence Paths near Zero Magnetic Field

We demonstrate a method to quantify and manipulate nuclear spin decoherence mechanisms that are active in zero to ultralow magnetic fields. These include: (i) non-adiabatic switching of spin quantization axis, due to residual background fields; (ii) scalar pathways due to through-bond couplings between $^1$H and heteronuclear spin species, such as $^2$H used partially as an isotopic substitute for $^1$H. Under conditions of free evolution, scalar relaxation due to $^2$H can significantly limit nuclear spin polarization lifetimes and thus the scope of magnetic resonance procedures near zero field. It is shown that robust trains of pulsed dc magnetic fields that apply $π$ flip angles to one or multiple spin species may switch effective symmetry of the nuclear spin Hamiltonian, imposing decoupled or coupled dynamic regimes on demand. The method should broaden the spectrum of hyperpolarized biomedical contrast-agent compounds and hyperpolarization procedures that are used near zero field.

physics.chem-ph↗

arXiv2021

Fast-field-cycling, ultralow-field nuclear magnetic relaxation dispersion

Optically pumped magnetometers (OPMs) based on alkali-atom vapors are ultra-sensitive devices for dc and low-frequency ac magnetic measurements. Here, in combination with fast-field-cycling hardware and high-resolution spectroscopic detection, we demonstrate applicability of OPMs in quantifying nuclear magnetic relaxation phenomena. Relaxation rate dispersion across the nT to mT field range enables quantitative investigation of extremely slow molecular motion correlations in the liquid state, with time constants >1 ms, and insight into the corresponding relaxation mechanisms. The 10-20 fT/$\sqrt{\mathrm{Hz}}$ sensitivity of an OPM between 10 Hz and 5.5 kHz $^1$H Larmor frequency suffices to detect magnetic resonance signals from $\sim$0.1 mL liquid volumes imbibed in simple mesoporous materials, or inside metal tubing, following nuclear spin prepolarization adjacent to the OPM. High-resolution spectroscopic detection can resolve inter-nucleus spin-spin couplings, further widening the scope of application to chemical systems. Expected limits of the technique regarding measurement of relaxation rates above 100 s$^{-1}$ are discussed.

physics.chem-ph↗

arXiv2018

Nanoscale spin manipulation with pulsed magnetic gradient fields from a hard disc drive writer

The individual and coherent control of solid-state based electron spins is important covering fields from quantum information processing and quantum metrology to material research and medical imaging. Especially for the control of individual spins in nanoscale networks, the generation of strong, fast and localized magnetic fields is crucial. Highly-engineered devices that demonstrate most of the desired features are found in nanometer size magnetic writers of hard disk drives (HDD). Currently, however, their nanoscale operation, in particular, comes at the cost of excessive magnetic noise. Here, we present HDD writers as a tool for the efficient manipulation of single as well as multiple spins. We show that their tunable gradients of up to 100 μT/nm can be used to spectrally address individual spins on the nanoscale. Their GHz Bandwidth allows to switch control fields within nanoseconds, faster than characteristic timescales such as Rabi and Larmor periods, spin-spin couplings or optical transitions, thus extending the set of feasible spin manipulations. We used the fields to drive spin transitions through non-adiabatic fast passages or enable the optical readout of spin states in strong misaligned fields. Building on these techniques, we further apply the large magnetic field gradients for microwave selective addressing of single spins and show its use for the nanoscale optical colocalization of two emitters.

physics.app-ph↗