Ivan V. Pechenezhskiy

Single-molecule-resolved structural changes induced by temperature and light in surface-bound organometallic molecules designed for energy storage

We have used scanning tunneling microscopy, Auger electron spectroscopy, and density functional theory calculations to investigate thermal and photoinduced structural transitions in (fulvalene)tetracarbonyldiruthenium molecules (designed for light energy storage) on a Au(111) surface. We find that both the parent complex and the photoisomer exhibit striking thermally induced structural phase changes on Au(111), which we attribute to the loss of carbonyl ligands from the organometallic molecules. Density functional theory calculations support this conclusion. We observe that UV exposure leads to pronounced structural change only in the parent complex, indicative of a photoisomerization reaction.

Phonon-Mediated Quasiparticle Poisoning of Superconducting Microwave Resonators

Nonequilibrium quasiparticles represent a significant source of decoherence in superconducting quantum circuits. Here we investigate the mechanism of quasiparticle poisoning in devices subjected to local quasiparticle injection. We find that quasiparticle poisoning is dominated by the propagation of pair-breaking phonons across the chip. We characterize the energy dependence of the timescale for quasiparticle poisoning. Finally, we observe that incorporation of extensive normal metal quasiparticle traps leads to a more than order of magnitude reduction in quasiparticle loss for a given injected quasiparticle power.

Intermolecular interactions and substrate effects for an adamantane monolayer on a Au(111) surface

We study theoretically and experimentally the infrared (IR) spectrum of an adamantane monolayer on a Au(111) surface. Using a new STM-based IR spectroscopy technique (IRSTM) we are able to measure both the nanoscale structure of an adamantane monolayer on Au(111) as well as its infrared spectrum, while DFT-based ab initio calculations allow us to interpret the microscopic vibrational dynamics revealed by our measurements. We find that the IR spectrum of an adamantane monolayer on Au(111) is substantially modified with respect to the gas-phase IR spectrum. The first modification is caused by the adamantane–adamantane interaction due to monolayer packing and it reduces the IR intensity of the 2912 cm 1 peak (gas phase) by a factor of 3.5. The second modification originates from the adamantane–gold interaction and it increases the IR intensity of the 2938 cm 1 peak (gas phase) by a factor of 2.6, and reduces its frequency by 276 cm 1 . We expect that the techniques described here can be used for an independent estimate of substrate effects and intermolecular interactions in other diamondoid molecules, and for other

Measurement of a superconducting qubit with a microwave photon counter

Counting the state of a qubit Operation of a quantum computer will be reliant on the ability to correct errors. This will typically require the fast, high-fidelity quantum nondemolition measurement of a large number of qubits. Opremcak et al. describe a method that uses a photon counter to determine the state of a superconducting qubit. Being able to simply read out the qubit state as a photon number removes the need for bulky components and large experimental overhead that characterizes present approaches. Science, this issue p. 1239 A microwave photon counter is used to determine the state of a superconducting qubit. Fast, high-fidelity measurement is a key ingredient for quantum error correction. Conventional approaches to the measurement of superconducting qubits, involving linear amplification of a microwave probe tone followed by heterodyne detection at room temperature, do not scale well to large system sizes. We introduce an approach to measurement based on a microwave photon counter demonstrating raw single-shot measurement fidelity of 92%. Moreover, the intrinsic damping of the photon counter is used to extract the energy released by the measurement process, allowing repeated high-fidelity quantum nondemolition measurements. Our scheme provides access to the classical outcome of projective quantum measurement at the millikelvin stage and could form the basis for a scalable quantum-to-classical interface.

Imaging structural transitions in organometallic molecules on Ag(100) for solar thermal energy storage

The use of opto-thermal molecular energy storage at the nanoscale creates new opportunities for powering future microdevices with flexible synthetic tailorability. Practical application of these molecular materials, however, requires a deeper microscopic understanding of how their behavior is altered by the presence of different types of substrates. Here, we present single-molecule-resolved scanning tunneling microscopy imaging of thermally- and optically-induced structural transitions in (fulvalene)tetracarbonyldiruthenium molecules adsorbed onto a Ag(100) surface as a prototype system. Both the parent complex and the photoisomer display distinct thermally-driven phase transformations when they are in contact with a Ag(100) surface. This behavior is consistent with the loss of carbonyl ligands due to strong molecule-surface coupling. Ultraviolet radiation induces marked structural changes only in the intact parent complex, thus indicating a photoisomerization reaction. These results demonstrate how stimuli-induced structural transitions in this class of molecule depend on the nature of the underlying substrate.