Philipp Haslinger

Recent advances in transmission electron microscopy (TEM) have opened the path toward spin resonance spectroscopy with single-spin sensitivity. To assess this potential, we investigate the quantum precision limits for sensing magnetic moments with free-electron probes. Using a scattering model where an electron wavepacket interacts with a localized spin, we study two metrological tasks: estimating the magnitude of the magnetic moment and discriminating the presence of a spin. The sensitivity for a given measurement setting is generally determined by the classical Fisher information, which we benchmark against the quantum bound optimized over all measurements. We find that conventional TEM imaging can saturate the quantum bound when backaction (BA) of the probe electron onto the spin state is negligible. We also find that, when BA is relevant, one could do better by realizing a measurement of the electron’s orbital angular momentum state. These results establish the quantum limits of spin sensing in TEM and guide the development of future experiments probing individual electron spins or nanoscale ensembles of nuclear spins.

Freely propagating electrons may serve as quantum probes that can become coherently correlated with other quantum systems, offering access to advanced metrological resources. We propose a setup that coherently couples free electrons in an electron microscope to a trapped-ion quantum processor, enabling nondestructive, quantum-coherent detection and the accumulation of information across multiple electrons. Our analysis shows that single electrons can induce resolvable qubit excitations, establishing a platform for practical applications such as quantum-enhanced, dose-efficient electron microscopy.

Coincidence imaging, also known as ghost imaging, is a technique that exploits correlations between two particles to reconstruct information about a specimen. The particle that relays the spatial information about the object remains completely noninteracting, while the particle used to probe the object is not spatially resolved. While ghost imaging has been primarily implemented on photonic platforms, applying it to particles with fundamentally different properties opens up scientific directions. Mixing massive, charged electrons with massless, neutral photons introduces a hybrid architecture that unites two fundamental microscopic platforms, each serving as a cornerstone of highly advanced imaging systems. In this work, we investigate coincidence imaging using electron–cathodoluminescence photon pairs generated within a transmission electron microscope. Utilizing a custom-built free-space cathodoluminescence setup, we demonstrate two-dimensional ghost imaging of complex patterns. We are able to obtain a spatial resolution down to 2 μ m , paving the way for adaptation of quantum-enhanced imaging techniques from photonic quantum optics to electron microscopy.

Coherent spin resonance techniques, such as nuclear and electron spin resonance spectroscopy, have revolutionized non-invasive imaging by providing spectrally resolved information about spin dynamics. Motivated by the recent emergence of electron microscopy methods capable of sensing microwave-excitations, we establish a theoretical framework for Spin Resonance Spectroscopy (SRS) in transmission electron microscopy (TEM). This technique combines microwave pump fields with focused electron probe beams to enable state-selective spin imaging at the atomic scale. Using scattering theory, we model the interaction between free-space electrons and electron spin systems, capturing both elastic and inelastic processes. The strongest effect of the spin system on the free electron is a magnetic phase shift. Our simulations demonstrate that phase shifts from individual electron spins are detectable in both image mode and diffraction mode. In principle, differential measurements under microwave control allow the extraction of local resonance frequencies that are influenced by the surrounding spin environment. By evaluating the Classical Fisher Information (CFI), we identify imaging conditions that maximize the signal-to-noise ratio (SNR), showing how defocus and beam width affect the measurement sensitivity. These findings establish a foundation for integrating SRS with high-resolution TEM, bridging spin spectroscopy and atomic-scale imaging, and enabling new capabilities in quantum spin research and nanoscale materials characterization.

We present a method that combines spin resonance spectroscopy with transmission electron microscopy (TEM), enabling localized in situ detection of microwave (MW)-driven spin transitions in the specimen, utilizing the free-space electron beam of the TEM as a signal receiver. Spin state polarization is achieved via the magnetic field of the TEM’s polepiece, while a custom-designed microresonator integrated into a TEM sample holder delivers continuous wave MW excitation at GHz frequencies. At resonance, the MW field drives spin transitions that produce a dynamic, precessional magnetic field around the specimen, inducing a deflection of the free-space electron beam. Phase-locked detection synchronized to the MW driving fields enables the isolation of spin precession contributions to the electron beam deflection. The presented technique offers a pathway for the in situ exploration of spin excitations at the nanoscale.

Freely propagating electrons may serve as quantum probes that can become coherently correlated with other quantum systems, offering access to advanced metrological resources. We propose a setup that coherently couples free electrons in an electron microscope to a trapped-ion quantum processor, enabling non-destructive, quantum-coherent detection and the accumulation of information across multiple electrons. Our analysis shows that single electrons can induce resolvable qubit excitations, establishing a platform for practical applications such as quantum-enhanced, dose-efficient electron microscopy.

Control of quantum systems typically relies on the interaction with electromagnetic radiation. In this study, we experimentally show that the electromagnetic near-field of a spatially modulated free-space electron beam can be used to drive spin systems, demonstrating free-electron-bound-electron resonant interaction. By periodically deflecting the electron beam of a scanning electron microscope in close proximity to a spin-active solid-state sample, and sweeping the deflection frequency across the spin resonance, we directly observe phase coherent coupling between the electron beam's near-field and the two spin states. This method relies only on classically shaping the electron beams transversal correlations and has the potential to enable coherent control of quantum systems with unprecedented, electron microscopic resolution, opening novel possibilities for advanced spectroscopic tools in nanotechnology.

We propose a scheme for generating high-mass quantum superposition states of an optically precooled, levitated nanoparticle through electron diffraction at its subnanometer crystal lattice. When a single electron undergoes Bragg diffraction at a free-falling nanoparticle, momentum conservation implies that the superposition of Bragg momenta is imprinted onto the relative coordinate between electron and nanoparticle, which entangles their wave functions. By imaging the electron interferogram, one maps the nanoparticle state onto a superposition of Bragg momenta, as if it was diffracted by its own lattice. This results in a coherent momentum splitting approximately 1000 times greater than what is achievable with two-photon recoils in conventional standing-wave gratings. Self-interference of the nanoparticle can thus be observed within drastically shorter free-fall times in a time-domain Talbot interferometer configuration, significantly relaxing source requirements and alleviating decoherence from environmental factors such as residual gas and thermal radiation. Shorter interference times also allow for a recapture of the nanoparticle within its initial trapping volume, facilitating its reuse in many rapid experimental duty cycles. This opens new possibilities for experimental tests of macroscopic quantum effects within a transmission electron microscope.