Manipulating Fock states of a harmonic oscillator while preserving its linearity

We present a new scheme for controlling the quantum state of a harmonic oscillator by coupling it to an anharmonic multilevel system (MLS) with first to second excited state transition frequency on-resonance with the oscillator. In this scheme that we call "ef-resonant", the spurious oscillator Kerr non-linearity inherited from the MLS is very small, while its Fock states can still be selectively addressed via an MLS transition at a frequency that depends on the number of photons. We implement this concept in a circuit-QED setup with a microwave 3D cavity (the oscillator, with frequency 6.4 GHz and quality factor QO=2E-6) embedding a frequency tunable transmon qubit (the MLS). We characterize the system spectroscopically and demonstrate selective addressing of Fock states and a Kerr non-linearity below 350 Hz. At times much longer than the transmon coherence times, a non-linear cavity response with driving power is also observed and explained.Comment: 8 pages, 5 figure

One hundred second bit-flip time in a two-photon dissipative oscillator

Current implementations of quantum bits (qubits) continue to undergo too many errors to be scaled into useful quantum machines. An emerging strategy is to encode quantum information in the two meta-stable pointer states of an oscillator exchanging pairs of photons with its environment, a mechanism shown to provide stability without inducing decoherence. Adding photons in these states increases their separation, and macroscopic bit-flip times are expected even for a handful of photons, a range suitable to implement a qubit. However, previous experimental realizations have saturated in the millisecond range. In this work, we aim for the maximum bit-flip time we could achieve in a two-photon dissipative oscillator. To this end, we design a Josephson circuit in a regime that circumvents all suspected dynamical instabilities, and employ a minimally invasive fluorescence detection tool, at the cost of a two-photon exchange rate dominated by single-photon loss. We attain bit-flip times of the order of 100 seconds for states pinned by two-photon dissipation and containing about 40 photons. This experiment lays a solid foundation from which the two-photon exchange rate can be gradually increased, thus gaining access to the preparation and measurement of quantum superposition states, and pursuing the route towards a logical qubit with built-in bit-flip protection

Catalyst preparation for CMOS-compatible silicon nanowire synthesis

Metallic contamination was key to the discovery of semiconductor nanowires, but today it stands in the way of their adoption by the semiconductor industry. This is because many of the metallic catalysts required for nanowire growth are not compatible with standard CMOS (complementary metal oxide semiconductor) fabrication processes. Nanowire synthesis with those metals which are CMOS compatible, such as aluminium and copper, necessitate temperatures higher than 450 C, which is the maximum temperature allowed in CMOS processing. Here, we demonstrate that the synthesis temperature of silicon nanowires using copper based catalysts is limited by catalyst preparation. We show that the appropriate catalyst can be produced by chemical means at temperatures as low as 400 C. This is achieved by oxidizing the catalyst precursor, contradicting the accepted wisdom that oxygen prevents metal-catalyzed nanowire growth. By simultaneously solving material compatibility and temperature issues, this catalyst synthesis could represent an important step towards real-world applications of semiconductor nanowires.Comment: Supplementary video can be downloaded on Nature Nanotechnology websit

Structural Properties of Tensile-Strained Si Layers Grown on Si_1-xGe_x Virtual Substrates (x = 0.2, 0.3, 0.4 and 0.5)

International audienceWe have studied the structural properties of tensile-strained Si (sSi) layers grown on polished Si0.8Ge0.2 and Si0.7Ge0.3 virtual substrates as a function of their thickness. The surface morphology, the tensile-strain, the linear density of defects and the threading dislocation density have been quantified for different sSi layer thickness. Results are compared to those previously obtained on sSi layers grown on top of polished Si0.6Ge0.4 and Si0.5Ge0.5 virtual substrates (ECS Trans. 3, No. 7, 319 (2006)

Large improvement of CNT yarn electrical conductivity by varying chemical doping and annealing treatment

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UV and Visible Raman Spectroscopy Applied to s-Si/Si_1-xGe_x and s-SOI Multi-layer Systems

International audienceMechanical strain can be used to improve electronic transport properties in advanced short gate length Si-based Metal Oxide Semiconductor Field Effect Transistors. The controlled introduction of strain in the channel area of transistors (thanks to recessed SiGe sources and drains, contact etch stop layers or to previous processing at the wafer scale) can indeed increase the carrier mobility by a factor of up to two. We have used here ultra-violet and visible Raman Spectroscopy to study the processes that can influence strain during the elaboration of strained Si On Insulator (sSOI) substrates. The results obtained during analyses of tensily-strained Si layers grown on polished Si1-xGex virtual substrates (VS) show that the strain can be preserved for 20% of Ge. However, we observed a relaxation of the strain for 40% Ge, after layer transfer onto oxidized silicon. A definite strain relaxation at the edges of lines patterned in sSOI wafers was also demonstrated. A good agreement between experimental results and simulation has been achieved

Stochastic Simulation and Single Events Kinetic Modeling: Application to Olefin Oligomerization

International audienceIn order to handle a tractable network for complex reaction systems such as oligomerization, stochastic tools are applied to reduce the reaction mechanism. The particularity of this work is that quantitative single event kinetic modeling constants are used to generate a network which correctly describes the dynamic behavior of the studied reacting system. By using the stochastic method, which is based on a probabilistic approach, we can avoid the generation of improbable reaction paths in order to reduce the network expansion. Comparison with a classical limited network shows that the proposed network generation technique can be more reliable. Alongside, the stochastic simulation algorithm can be used as a method of simulation instead of the deterministic method because of the huge size of the oligomerization network

Effect of the annealing treatment on the physical and structural properties of LiNbO3 thin films deposited by radio-frequency sputtering at room temperature

International audienceReaching the full potential of the 5th Generation of mobile applications (5G) requires pushing the performances of acoustic radio-frequency (RF) filters beyond their current limits. Current high-performances RF filters (above 2.5 GHz) are based on aluminium nitride (AlN). Their bandwidth is however limited by the low electromechanical coupling coefficient of AlN. In this context, due to its higher electromechanical coupling coefficient, lithium niobate (LiNbO3) is a good candidate as an active piezoelectric material. For this application, LiNbO3 films need to be stoichiometric and to be either highly textured or monocrystalline. However, there seems to be no deposition process for high quality LiNbO3 thin films on silicon available at the moment, which could be mainly due to the difficulty to achieve a high crystalline quality and to the challenging control and of its stoichiometry. In the present work, the realization of highly textured films deposited directly on silicon substrate by RF sputtering at room temperature and after annealing was demonstrated. The effect of the annealing parameters (temperature and ramping rates) was studied. LiNbO3 layers with a strong degree of texture along the c-axis were obtained. The X-ray diffraction analysis showed that an optimum texture of 99% can be reached by a high temperature of annealing and a fast temperature ramping rate. The effect of annealing parameters on the presence of secondary phase LiNb3O8 and film density was also investigated

Microstructural and chemical analysis of polycrystalline LiNbO₃ films obtained by room-temperature RF sputtering after various annealing durations

International audienceThe development of materials for industrial applications is in constant evolution. Regarding environmental or health laws, the use of some materials is restricted (lead-based). In this context, lithium niobate (LiNbO3) is studied in order to develop the performances of the RF (radio frequency) applications (for instance, filters using the bulk acoustic wave or surface acoustic wave technology). The deposition of LiNbO3 is mainly performed by chemical or physical vapor deposition and solgel techniques, resulting in polycrystalline films with or without a preferred orientation. For RF applications, LiNbO3 films need to be highly textured with a preferred orientation among the (006) plane in order to maximize the electrical response. In the present work, 150 nm thick LiNbO3 films were grown by RF sputtering at room temperature on Si substrates with native SiO2. The films were annealed at 950 °C, with an original process, for various durations. Polycrystalline yet (006) preferentially oriented LiNbO3 films were obtained on silicon. The properties of the as-deposited and annealed films were analyzed by x-ray diffraction (XRD), Raman spectroscopy, secondary ion mass spectrometry (SIMS), and scanning electron microscopy (SEM). The annealing treatment effect was highlighted by symmetric XRD analysis. The adhesion of the films is confirmed by SEM analysis. The diffusion profile of Li was characterized by SIMS and XPS analyses. This process, mainly based on a specific annealing treatment, leads to the synthesis of nearly stoichiometric LiNbO3 on silicon, and the effect of the thermal treatment on the texture of the film is highlighted

Ge Enrichment Technique on SiGe/SOI Mesa Islands: a Localized GeOI Structures Fabrication Method

International audienceThis paper presents a review of the mechanisms involved in the oxidation of SiGe/SOI mesa structures. This method, called local Ge enrichment technique is proposed to carry out GeOI structures on SOI wafers to allow planar SOI-GeOI co-integration. Two types of mechanisms have been identified, defined by their respective scale. Small scaled mechanisms (nanometer range) involve additional oxidations critical for mesa size and shape preservation. Large scaled mechanisms (micrometer range) involve non homogeneous Ge spatial distributions on the enriched mesa