Universal quantum control of an atomic spin qubit on a surface

Scanning tunneling microscopy (STM) enables the bottom-up fabrication of tailored spin systems on a surface that are engineered with atomic precision. When combining STM with electron spin resonance (ESR), these single atomic and molecular spins can be controlled quantum-coherently and utilized as electron-spin qubits. Here we demonstrate universal quantum control of such a spin qubit on a surface by employing coherent control along two distinct directions, achieved with two consecutive radio-frequency (RF) pulses with a well-defined phase difference. We first show transformations of each Cartesian component of a Bloch vector on the quantization axis, followed by ESR-STM detection. Then we demonstrate the ability to generate an arbitrary superposition state of a single spin qubit by using two-axis control schemes, in which experimental data show excellent agreement with simulations. Finally, we present an implementation of two-axis control in dynamical decoupling. Our work extends the scope of STM-based pulsed ESR, highlighting the potential of this technique for quantum gate operations of electron-spin qubits on a surface

Design and Characterization of an Electrically Powered Single Molecule on Gold

The surface diffusion of individual molecules is of paramount importance in self-assembly processes and catalytic processes. However, the fundamental understanding of molecule diffusion peculiarities considering conformations and adsorption sites remain poorly known at the atomic scale. Here, we probe the 4′-(4-tolyl)-2,2′:6′,2″-terpyridine adsorbed on the Au(111) herringbone structure combining scanning tunneling microscopy and atomic force microscopy. Molecules are controllably translated by electrons excitations over the reconstruction, except at elbows acting as pinning centers. Experimental data supported by theoretical calculations show the formation of coordination bonds between the molecule and Au atoms of the surface. Using force spectroscopy, we quantify local variation of the surface potential and the lateral force required to move the molecule. We found an elevation of the diffusion barrier at elbows of the reconstruction of ∼100 meV compared to the rest of the surface

On-Surface Atom-by-Atom-Assembled Aluminum Binuclear Tetrabenzophenazine Organometallic Magnetic Complex

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Low temperature two STM tip tunneling measurements of a floating chemical potential Pb(111) surface

On a Pb(111) superconducting surface, low temperature dI/dV tunnelling spectra are recorded between two scanning tunnelling microscopes (STM) metallic tips with the Pb(111) sample metallic support non-grounded. The tunnelling current intensity I passing between the 2 tips through the sample is controlled by changing one or both STM vacuum tunnelling junction resistances. The chemical potential of this floating Pb(111) surface depends on the normalized ratio between those two quantum resistances. When ungrounded, the Pb(111) sample chemical potential balances between those of the 2 STM tips while tuning their respective tip end atomic apex to Pb(111) surface distances with a picometer precision without any physical contact between the STM tips and the surface

A Tetrabenzophenazine Low Voltage Single Molecule XOR Quantum Hamiltonian Logic Gate

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Train of Single Molecule-Gears

International audienceTwo molecule-gears, 1.2 nm in diameter with 6 teeth, are mounted each on a single copper ad-atom separated exactly by 1.9 nm on a lead surface using a low temperature scanning tunneling microscope (LT-STM). A functioning train of 2 molecule-gears is constructed completed with a molecule-handle. Not mounted on a Cu ad-atom axle, this ancillary molecule-gear is mechanically engaged with the first molecule-gear of the train to stabilize its step by step rotation. Centered on its Cu ad-atom axle, the rotation of the first gear of the train step by step rotates the second similar to a train of macroscopic gears. From the handle to the first and to this second molecule-gear, the exact positioning of the two Cu ad-atom axles on the lead surface ensures that the molecular teeth to teeth mechanics is fully reversible

Long and isolated graphene nanoribbons by on-surface polymerization on Au(111)

Abstract Low electronic gap graphene nanoribbons (GNRs) are used for the fabrication of nanomaterial-based devices and, when isolated, for mono-molecular electronics experiences, for which a well-controlled length is crucial. Here, an on-surface chemistry protocol is monitored for producing long and well-isolated GNR molecular wires on an Au(111) surface. The two-step Ullmann coupling reaction is sequenced in temperature from 100 °C to 350 °C by steps of 50 °C, returning at room temperature between each step and remaining in ultrahigh vacuum conditions. After the first annealing step at 100 °C, the monomers self-organize into 2-monolayered nano-islands. Next, the Ullmann coupling reaction takes place in both 1st and 2nd layers of those nano-islands. The nano-island lateral size and shape are controlling the final GNR lengths. Respecting the above on-surface chemistry protocol, an optimal initial monomer coverage of ~1.5 monolayer produces isolated GNRs with a final length distribution reaching up to 50 nm and a low surface coverage of ~0.4 monolayer suitable for single molecule experiments

On-surface Double layer polymerization enhancing GNR lengths on an Au(111) surface

By performing controlled step-by-step annealing experiments of bilayers of GNR monomer reactants with multiple UHV-STM analysis of intermediate stages, we show that the coupling reaction takes place mainly in the uppermost layer of the monomer bilayer despite being separated from the Au(111) surface by the lowermost compact monomer carpet. This demonstrates that the initial monomer bilayer configuration plays acrucial role in lengthening the final GNR length once the intermediate dehalogenated polymer is cyclodehydrogenated. In this respect our experimental results directly provide the counter rationalization to the generalization of the metallic substrate catalytic role in the surface assisted coupling chemical reactions

On-surface Double layer polymerization enhancing GNR lengths on an Au(111) surface

By performing controlled step-by-step annealing experiments of bilayers of GNR monomer reactants with multiple UHV-STM analysis of intermediate stages, we show that the coupling reaction takes place mainly in the uppermost layer of the monomer bilayer despite being separated from the Au(111) surface by the lowermost compact monomer carpet. This demonstrates that the initial monomer bilayer configuration plays acrucial role in lengthening the final GNR length once the intermediate dehalogenated polymer is cyclodehydrogenated. In this respect our experimental results directly provide the counter rationalization to the generalization of the metallic substrate catalytic role in the surface assisted coupling chemical reactions

On-surface Double layer polymerization enhancing GNR lengths on an Au(111) surface

By performing controlled step-by-step annealing experiments of bilayers of GNR monomer reactants with multiple UHV-STM analysis of intermediate stages, we show that the coupling reaction takes place mainly in the uppermost layer of the monomer bilayer despite being separated from the Au(111) surface by the lowermost compact monomer carpet. This demonstrates that the initial monomer bilayer configuration plays acrucial role in lengthening the final GNR length once the intermediate dehalogenated polymer is cyclodehydrogenated. In this respect our experimental results directly provide the counter rationalization to the generalization of the metallic substrate catalytic role in the surface assisted coupling chemical reactions