arXiv subjects

Robert Smit

Publications and source records attributed to Robert Smit.

6 recordsLinked to original sources

arXiv2026

On-chip levitation of ferromagnetic microparticles

Levitation of microscopic objects in vacuum combines exceptional environmental isolation with precise control of their dynamics, pushing the limits of sensing and macroscopic quantum physics. In particular, magnetic levitation allows a large range of particle sizes, while avoiding detrimental effects from high-intensity optical trapping beams and electric field noise. However, existing diamagnetic and Meissner levitation approaches are typically constrained by low mechanical eigenfrequencies, limited integrability with other systems due to bulky coils or magnets, and, for Meissner levitation, the need for cryogenic operation. Here, we demonstrate a room-temperature on-chip magnetic levitation platform capable of stably levitating a nanogram (6.5 micrometer radius) ferromagnetic microsphere. The platform is scalable and tunable, and supports librational modes with eigenfrequencies exceeding 10 kHz. Further miniaturization and coupling to solid-state spin qubits could enable cooling to the quantum ground state. Beyond quantum experiments, this architecture enables integrated precision sensing and studies of isolated ferromagnet thermodynamics.

quant-ph↗

arXiv2025

Towards all-optical spin manipulation in single molecules: a refined region for locating a dark resonance

The on-demand manipulation of triplet states in closed-shell single molecules is still out of reach due to a lack of information about the energy of those triplet states. Yet, the access to triplet states would open up a route towards an all-optical single-molecule photonic switch/transistor and, moreover, would provide a way of performing coherent spin operations from the spin-less ground state. In this work, we take an important step towards those aims by measuring the triplet energy from the weak phosphorescence signal of perdeuterated perylene, embedded as a guest molecule in a dibenzothiophene host matrix, which well preserves the coherence properties of the perylene guest. We find that perylene's phosphorescence can be enhanced in this host matrix, when acting as an intermediary for the generation of triplet excitons. The triplet energy that we find can be used to significantly narrow down the search for the ultra-weak spin-forbidden transitions from the ground singlet to the triplet states of a single molecule.

physics.chem-ph↗

arXiv2025

Superconducting flux concentrator coils for levitation of particles in the Meissner state

Magnetic levitation of superconductors is a promising platform to study quantum mechanics in the large-mass limit. One major limitation is the weak trapping potential, which results in low vibrational eigenfrequencies and increased susceptibility to low-frequency noise. While generating strong magnetic fields is relatively straightforward, creating a tightly confined harmonic potential - essentially achieving a large magnetic field gradient - remains a significant challenge. In this work, we demonstrate a potential solution using superconducting cores that concentrate magnetic flux into arbitrarily small volumes. We show the ability to trap superconducting particles using an anti-Helmholtz coil configuration incorporating these cores. However, we observe rapid damping of the levitated particle motion due to flux trapping within the cores, occurring once the lower critical field is exceeded locally. To investigate this mechanism, we employ diamond NV center magnetometry and detect substantial remanent fields persisting after high-current operation of the coils. Finally, we discuss possible strategies to mitigate this effect and improve the levitation properties.

quant-ph↗

arXiv2025

Optical detection of charge defects near a graphene transistor using the Stark shift of fluorescent molecules

Two-dimensional crystals and their heterostructures unlock access to a class of photonic devices, bringing nanophotonics from the nanometer scale down to the atomic level where quantum effects are relevant. Single-photon emitters (SPEs) are central in quantum photonics as quantum markers linked to their electrostatic, thermal, magnetic, or dielectric environment. This aspect is exciting in two-dimensional (2D) crystals and their heterostructures, where the environment can be abruptly modified through vertical stacking or lateral structuring, such as moir\'e or nano-patterned gates. To further develop 2D-based quantum photonic devices, there is a need for quantum markers that are capable of integration into various device geometries, and that can be read out individually, non-destructively, and without additional electrodes. Here, we show how to optically detect charge carrier accumulation using sub-GHz linewidth single-photon emitters coupled to a graphene device. We employ the single molecule Stark effect, sensitive to the electric fields generated by charge puddles, such as those at the graphene edge. The same approach enables dynamic sensing of electronic noise, and we demonstrate the optical read-out of low-frequency white noise in a biased graphene device. The approach described here can be further exploited to explore charge dynamics in 2D heterostructures using quantum emitter markers.

cond-mat.mes-hall↗

arXiv2024

Characterisation of a levitated sub-mg ferromagnetic cube in a planar alternating-current magnetic Paul trap

Microscopic levitated objects are a promising platform for inertial sensing, testing gravity at small scales, optomechanics in the quantum regime, and large-mass superpositions. However, existing levitation techniques harnessing optical and electrical fields suffer from noise induced by elevated internal temperatures and charge noise, respectively. Meissner-based magnetic levitation circumvents both sources of decoherence but requires cryogenic environments. Here we characterize a sub-mg ferromagnetic cube levitated in an alternating-current planar magnetic Paul trap at room temperature. We show behavior in line with the Mathieu equations and quality factors of up to 2500 for the librational modes. Besides technological sensing applications, this technique sets out a path for MHz librational modes in the micron-sized particle limit, allowing for magnetic coupling to superconducting circuits and spin-based quantum systems.

quant-ph↗

arXiv2022

Sharp zero-phonon lines of single organic molecules on a hexagonal boron-nitride surface

Single fluorescent molecules embedded in the bulk of host crystals have proven to be excellent probes of the dynamics in their nano environment, thanks to their narrow (about 0.1 {\mu}eV) optical linewidth of the 0-0 zero-phonon line (0-0 ZPL) at cryogenic temperatures. However, the optical linewidths of the 0-0 ZPL have been found to increase dramatically as the single molecules are located closer to a surface or interface, while no 0-0 ZPL has been detected for organic molecules on any surface. Here, we study single fluorescent terrylene molecules adsorbed on the surface of hexagonal boron-nitride (hBN) substrates. Our low-temperature results show for the first time the observation of the 0-0 ZPL of fluorescent molecules on a surface. With resonant excitation, we find 0-0 ZPL linewidths down to values that are about 10 times larger than the Fourier limit of 45 +/- 3 MHz, dictated by the fluorescence lifetime. We compare our results for molecules deposited on the surfaces of annealed and non-annealed hBN flakes and we see a marked improvement in the spectral stability of the emitters after annealing. Our high-resolution spectra obtained on terrylene suggest the possibility of employing hBN in combination with a wide variety of single molecule emitters for investigation of physical phenomena at surfaces or for use in nanophotonic devices.

physics.chem-ph↗