arXiv subjects

Eric Bonvin

Publications and source records attributed to Eric Bonvin.

7 recordsLinked to original sources

arXiv2025

Trap-to-trap free falls with an optically levitated nanoparticle

We perform free-fall experiments with a charge-neutral, optically levitated nanoparticle. This is achieved using an optical tweezer that can be rapidly toggled on and off and vertically displaced, enabling the particle to be released and recaptured after each free fall. The particle is insensitive to electric fields due to its charge neutrality and, during free evolution, is not subject to photon recoil heating. We achieve free-fall durations of up to 0.25 ms and observe a nearly two hundred-fold increase in the particle's position uncertainty at recapture. The current limit on the free-fall time arises from the performance of the initial cooling step. By implementing linear feedback techniques and reducing the background pressure, we expect to perform millisecond-scale free-fall experiments in ultra-high vacuum, opening new opportunities for generating large delocalizations of levitated objects.

quant-ph↗

arXiv2023

State Expansion of a Levitated Nanoparticle in a Dark Harmonic Potential

Levitated nanoparticles in vacuum are prime candidates for generating macroscopic quantum superposition states of massive objects. Most protocols for preparing these states necessitate coherent expansion beyond the scale of the zero-point motion to produce sufficiently delocalized and pure phase-space distributions. Here, we spatially expand and subsequently recontract the thermal state of a levitated nanoparticle by modifying the stiffness of the trap holding the particle. We achieve state-expansion factors of 25 in standard deviation for a particle initially feedback-cooled to a center-of-mass thermal state of \SI{155}{\milli\kelvin}. Our method relies on a hybrid scheme combining an optical trap, for cooling and measuring the particle's motion, with a Paul trap for expanding its state. Consequently, state expansion occurs devoid of measurement backaction from photon recoil, making this approach suitable for coherent wavefunction expansion in future experiments.

quant-ph↗

arXiv2023

Hybrid Paul-optical trap with large optical access for levitated optomechanics

We present a hybrid trapping platform that allows us to levitate a charged nanoparticle in high vacuum using either optical fields, radio-frequency fields, or a combination thereof. Our hybrid approach combines an optical dipole trap with a linear Paul trap while maintaining a large numerical aperture (0.77 NA). We detail a controlled transfer procedure that allows us to use the Paul trap as a safety net to recover particles lost from the optical trap at high vacuum. The presented hybrid platform adds to the toolbox of levitodynamics and represents an important step towards fully controllable dark potentials, providing control in the absence of decoherence due to photon recoil.

quant-ph↗

arXiv2023

Surface-Sensitive Raman Scattering by Transferable Nanoporous Plasmonic Membranes

Raman spectroscopy is a powerful technique to characterize materials. It probes non-destructively chemical composition, crystallinity, defects, strain and coupling phenomena. However, the Raman response of surfaces or thin films is often weak and obscured by dominant bulk signals. Here we overcome this limitation by placing a transferable porous gold membrane (PAuM) on top of the surface of interest. Slot-like nanopores in the membrane act as plasmonic slot antennas and enhance the Raman response of the surface or thin film underneath. Simultaneously, the PAuM suppresses the penetration of the excitation laser into the bulk, efficiently blocking the bulk Raman signal. Using graphene as a model surface, we show that these two simultaneous effects lead to an increase in the surface-to-bulk Raman signal ratio by three orders of magnitude. We find that 90% of the Raman enhancement occurs within the top 2.5 of the material, demonstrating truly surface-sensitive Raman scattering. To validate our approach, we analyze the surface of a LaNiO3 thin film. We observe a Raman mode splitting for the LaNiO3 surface-layer, which is spectroscopic evidence that the surface structure differs from the bulk. This result underpins that PAuM give direct access to Raman signatures of surfaces and their structural properties.

cond-mat.mtrl-sci↗

arXiv2019

One-dimensional edge contacts to a monolayer semiconductor

Integration of electrical contacts into van der Waals (vdW) heterostructures is critical for realizing electronic and optoelectronic functionalities. However, to date no scalable methodology for gaining electrical access to buried monolayer two-dimensional (2D) semiconductors exists. Here we report viable edge contact formation to hexagonal boron nitride (hBN) encapsulated monolayer MoS$_2$. By combining reactive ion etching, in situ Ar$^+$ sputtering and annealing, we achieve a relatively low edge contact resistance, high mobility (up to ~30 cm$^2$/Vs) and high on-current density (>50 uA/um at V$_{\rm DS}$ = 3V), comparable to top contacts. Furthermore, the atomically smooth hBN environment also preserves the intrinsic MoS$_2$ channel quality during fabrication, leading to a steep subthreshold swing of 116 mV/dec with a negligible hysteresis. Hence, edge contacts are highly promising for large-scale practical implementation of encapsulated heterostructure devices, especially those involving air sensitive materials, and can be arbitrarily narrow, which opens the door to further shrinkage of 2D device footprint.

cond-mat.mtrl-sci↗

arXiv2018

Quantized optical near-field interactions measured with a superconducting nanowire detector

The quantum nature of optical near-fields is interesting from a theoretical perspective and of importance for practical applications, such as high-resolution imaging, sensing and antenna-coupled quantum light sources. In this work we use a custom-designed superconducting nanowire single-photon detector (SNSPD) to directly read out the near-field interaction between source and detector. We use a subwavelength-sized aperture at the end of an optical fiber to record spatial near-field maps and to measure the distance dependence of the optical near-field interaction. Our measurements can be well described by a superposition of evanescent source fields with no noticeable probe-sample coupling. Our approach can be used for further studies of quantum near-field interactions and for the development of near-field imaging techniques with single quantum sensitivity.

physics.app-ph↗

arXiv2016

Controlled growth of CH$_3$NH$_3$PbI$_3$ nanowires in arrays of open nanofluidic channels

Spatial positioning of nanocrystal building blocks on a solid surface is a prerequisite for assembling individual nanoparticles into functional devices. Here, we report on the graphoepitaxial liquid-solid growth of nanowires of the photovoltaic compound CH$_3$NH$_3$PbI$_3$ in open nanofluidic channels. The guided growth, visualized in real-time with a simple optical microscope, undergoes through a metastable solvatomorph formation in polar aprotic solvents. The presently discovered crystallization leads to the fabrication of mm2-sized surfaces composed of perovskite nanowires having controlled sizes, cross-sectional shapes, aspect ratios and orientation which have not been achieved thus far by other deposition methods. The automation of this general strategy paves the way towards fabrication of wafer-scale perovskite nanowire thin films well-suited for various optoelectronic devices, e.g. solar cells, lasers, light-emitting diodes and photodetectors.

cond-mat.mes-hall↗