Taeyoung Choi

We demonstrate entangling quantum gates within a chain of five trapped ion qubits by optimally shaping optical fields that couple to multiple collective modes of motion. We individually address qubits with segmented optical pulses to construct multipartite entangled states in a programmable way. This approach enables high-fidelity gates that can be scaled to larger qubit registers for quantum computation and simulation.

Single tetracyanoethyelene (TCNE) molecules on Cu(111) are reversibly switched among five states by applying voltage pulses with the tip of a scanning tunneling microscope. A pronounced Kondo resonance in tunneling spectroscopy indicates that one of the states is magnetic. Side bands of the Kondo resonance appear at energies which correspond to inter- and intramolecular vibrational modes. Density functional theory suggests that molecular deformation changes the occupancy in TCNE's molecular orbi

Control of single electron spins constitutes one of the most promising platforms for spintronics, quantum sensing, and quantum information processing. Utilizing single molecular magnets as their hosts establishes an interesting framework since their molecular structure is highly flexible and chemistry-based large-scale synthesis directly provides a way toward scalability. Here, we demonstrate coherent spin manipulation of single molecules on a surface, which we control individually using a scann

Spin resonance of single spin centers bears great potential for chemical structure analysis, quantum sensing, and quantum coherent manipulation. Essential for these experiments is the presence of a two-level spin system whose energy splitting can be chosen by applying a magnetic field. In recent years, a combination of electron spin resonance (ESR) and scanning tunneling microscopy (STM) has been demonstrated as a technique to detect magnetic properties of single atoms on surfaces and to achieve

Atomic scale engineering of magnetic fields is a key ingredient for miniaturizing quantum devices and precision control of quantum systems. This requires a unique combination of magnetic stability and spin-manipulation capabilities. Surface-supported single atom magnets offer such possibilities, where long temporal and thermal stability of the magnetic states can be achieved by maximizing the magnet/ic anisotropy energy (MAE) and by minimizing quantum tunnelling of the magnetization. Here, we sh

Scanning tunneling microscopy is used to characterize the electronic structure of 1 ML films of c(2×2)N∕Cu(100) (i.e., Cu2N). By varying nitrogen coverage, a variety of morphologies are prepared, including (1) isolated ∼25nm2 islands, (2) close-packed arrays of islands, and (3) quasicontinuous monolayer films. In all three regimes, the authors find that Cu2N acts as an insulator, with a band gap that exceeds 4eV. The insulating Cu2N films are used to control the coupling of adsorbed Co atoms to

The magnetic properties of molecular structures can be tailored by chemical synthesis or bottom-up assembly at the atomic scale. We used scanning tunneling microscopy to study charge and spin transfer in individual complexes of transition metals with the charge acceptor, tetracyanoethylene (TCNE). The complexes were formed on a thin insulator, Cu2N on Cu(100), by manipulation of individual atoms and molecules. The Cu2N layer decouples the complexes from Cu electron density, enabling direct imagi

Investigating the quantum properties of individual spins adsorbed on surfaces by electron spin resonance combined with scanning tunneling microscopy (ESR-STM) has shown great potential for the development of quantum information technology on the atomic scale. A magnetic tip exhibiting high spin polarization is critical for performing an ESR-STM experiment. While the tip has been conventionally treated as providing a static magnetic field in ESR-STM, it was found that the tip can exhibit bistabil

Changes in data marks and groove structures are examined when a high power laser beam (>0.5 W) is focused on compact disk recordable (CD-R) data layers. Observations are recorded as a function of exposure condition and the type of dye used in the recording layer. All samples experience a decrease in the depths of data mark features and the pregroove modulations on exposure. Data marks on cyanine- and azo-dye disks become optically invisible after exposure, while data marks on phthalocyanine-dye

Scanning tunneling microscopy and spectroscopy were performed to study transition metal adatoms (Fe, Co, Cu) and individual metal-dithiol complexes on insulating Cu2N islands. Adsorption of metal adatoms on Cu2N is surprisingly complex and in the case of Fe, we find two distinct adsorption states for each of two distinct adsorption sites. Connection of these metal adatoms to dithiol molecules was pursued to model a single molecule junction, with the aim of understanding further details about the

Single spins are considered as a versatile candidate for miniaturizing information devices down to the nanoscale. To engineer the spin's properties, metal-organic frameworks provide a promising route which in turn requires thorough understanding of the metal-molecule interaction. Here, we investigate the magnetic robustness of a single iron (Fe) atom in artificially built Fe-tetracyanoethylene (TCNE) complexes by using low-temperature scanning tunneling microscopy (STM). We find that the magneti

Abstract Electron spin resonance (ESR) spectroscopy is a crucial tool to determine the chemical structure of materials. ESR spectra measured in molecular systems, however, are established on large ensembles of spins and usually require complicated structural analysis. Recently, scanning tunneling microscopy (STM) combined with ESR has been proven as a powerful tool to image and coherently control individual atomic spins on surfaces. Here, we extend this technique to demonstrate ESR on single org