Laetitia Pascal

High quality factor single-crystal diamond mechanical resonators

Single-crystal diamond is a promising material for microelectromechanical systems (MEMs) because of its low mechanical loss, compatibility with extreme environments, and built-in interface to high-quality spin centers. But its use has been limited by challenges in processing and growth. We demonstrate a wafer bonding-based technique to form diamond on insulator, from which we make single-crystal diamond micromechanical resonators with mechanical quality factors as high as 338 000 at room temperature. Variable temperature measurements down to 10 K reveal a nonmonotonic dependence of quality factor on temperature. These resonators enable integration of single-crystal diamond into MEMs technology for classical and quantum applications.

Circuit approach to photonic heat transport

We discuss the heat transfer by photons between two metals coupled by a linear element with a reactive impedance. Using a simple circuit approach, we calculate the spectral power transmitted from one resistor to the other and find that it is determined by the photon transmission coefficient, which depends on the impedances of the metals and the coupling element. We study the total photonic power flow for different coupling impedances, both in the linear regime, where the temperature difference between the metals is small, and in the non-linear regime of large temperature differences.

Efficiency of quasiparticle evacuation in superconducting devices

In a normal metal - insulator - superconductor (N-I-S) junction, charge transport is mainly governed by quasi- particles (1). The presence of the superconducting en- ergy gapinduces an energy selectivity of quasiparticles tunneling out of the normal metal (2, 3). The quasiparti- cle tunnel current is thus accompanied by a heat trans- fer from the normal metal to the superconductor that is maximum at a voltage bias just below the superconduct- ing gap (V ≤ �/e). For a double junction geometry (S-

Etching suspended superconducting tunnel junctions from a multilayer

A method to fabricate large-area superconducting hybrid tunnel junctions with a suspended central normal metal part is presented. The samples are fabricated by combining photo-lithography and chemical etch of a superconductor—insulator—normal metal multilayer. The process involves few fabrication steps, is reliable and produces extremely high-quality tunnel junctions. Under an appropriate voltage bias, a significant electronic cooling is demonstrated. We analyze semi-quantitatively the thermal behavior of a typical device.

Subkelvin tunneling spectroscopy showing Bardeen-Cooper-Schrieffer superconductivity in heavily boron-doped silicon epilayers

Scanning tunneling spectroscopies in the subkelvin temperature range were performed on superconducting silicon epilayers doped with boron in the atomic percent range. The resulting local differential conductance behaved as expected for a homogeneous superconductor, with an energy-gap dispersion below

Existence of an Independent Phonon Bath in a Quantum Device

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Hysteresis in superconducting short weak links and µ-SQUIDs

. The spectral shape, the amplitude, and temperature dependence of the superconductivity gap follow the BCS model, bringing support to the hypothesis of a hole pairing mechanism mediated by phonons in the weak-coupling limit.

Two-dimensional nanoscale imaging of gadolinium spins via scanning probe relaxometry with a single spin in diamond

At low temperatures, the thermal wavelength of acoustic phonons in a metallic thin film on a substrate can widely exceed the film thickness. It is thus generally believed that a mesoscopic device operating at low temperature does not carry an individual phonon population. In this work, we provide direct experimental evidence for the thermal decoupling of phonons in a mesoscopic quantum device from its substrate phonon heat bath at a sub-Kelvin temperature. A simple heat balance model assuming an independent phonon bath following the usual electron-phonon and Kapitza coupling laws can account for all experimental observations.