- Accueil
- Institut Néel
- Équipes de recherche
- Pôles & Services techniques
- Travailler à l’institut
- Partenariats
- Actualités
- Agenda
- Annuaire
La présentation sera faite en anglais.
Résumé : Superconducting Josephson parametric amplifiers allow the addition of the minimum amount of noise permitted by quantum mechanics in the amplification process. As such, they are now essential in quantum bit readout and microwave quantum optics experiments when the signal of interest is below the noise floor of standard cryogenic amplifiers. A typical superconducting parametric amplifier, when operated as a resonant amplifier, consists of a microwave cavity in which a tunnel Josephson junction is inserted to introduce non-linearity. As this amplification process relies on a resonant phenomenon, the bandwidth is intrinsically limited to a few MHz. New designs of flux-tunable and wide-band traveling-wave parametric amplifiers have been created to circumvent this issue.
Another approach that recently sparked a significant interest, is to introduce a semiconducting weak link in the Josephson junction. The presence of the semiconductor allows for its transport properties, such as non-linearity or critical current, to be tuned using the electric field generated by a gate voltage. Recent implementations of this idea have led to the development of gate tunable Josephson parametric amplifiers (JPAs) using graphene and planar InAs. Among hybrid superconductor-semiconductor (Sc-Sm) devices, InAs nanowires with epitaxial aluminum have been widely used in gate-tunable quantum bits as they provide a defect-free Sc-Sm interface and the nanowire geometry allows for an easy transfer onto a substrate suitable for microwave circuits with low dielectric loss. In a Josephson junction, the amount of non-linearity usually scales inversely with the critical current of the junction. While one-dimensional semiconductor nanowire weak links can provide a large non-linearity (small critical current), suitable for realizing quantum bits, this large non-linearity is a challenge in building a parametric amplifier. This explains why they have not been used in Josephson parametric amplifiers yet.
During this thesis, we have fabricated Josephson junctions constituted of parallel InAs semiconducting nanowires that feature a large critical current and a reduced non-linearity, not hitherto realized with single nanowires. We will also present results on the growth of parallel nanowires by Molecular Beam Epitaxy. By integrating the Josephson junctions in a microwave resonator, we demonstrate, in optimal conditions, a parametric gain exceeding 20 dB where the frequency of amplification can be tuned by varying the voltage applied to the gate electrode. We show that using this amplifier improves the signal-to-noise ratio of the measurement chain compared to a standard cryogenic amplifier, highlighting its potentially quantum-limited behavior.
