Noise Correlations in Three-Terminal Diffusive Superconductor–Normal-Metal–Superconductor Nanostructures

Abstract

We present measurements of current noise and cross-correlations in three-terminal Superconductor-Normal metal-Superconductor (S-N-S) nanostructures that are potential solid-state entanglers thanks to Andreev reflections at the N-S interfaces. The noise correlation measurements spanned from the regime where electron-electron interactions are relevant to the regime of Incoherent Multiple Andreev Reflection (IMAR). In the latter regime, negative cross-correlations are observed in samples with closely-spaced junctions.

Subgap structure in the conductance of a three-terminal Josephson junction

“…Here and in the following, the voltage range was limited to ±40 µV because going beyond would require a d.c. current close to the superconducting electrodes depairing current [18]. As the investigated voltage range remains well below the superconductor energy gap, the number of multiple Andreev reflections (∼ 2∆/eV ) necessary for a quasiparticle to reach the superconducting gap is more than 8, which would correspond to a total diffusion time much larger than the inelastic scattering time.…”

“…Another situation is met in mesoscopic three-terminal Josephson junctions in which a single normal conductor is connected to three superconducting contacts [16][17][18][19][20]. The transport properties then depend on two independent (phase or voltage) variables.…”

A ballistic two-dimensional-electron-gas Andreev interferometer

“…We measured a sizeable sensitivity to magnetic flux with a maximum value of the transfer function dV /dΦ ∼ 25 µV/Φ 0 and a low flux noise down to ∼ 80 µΦ 0 / √ Hz. Our system can operate from the miliKelvin regime up to T ∼ 7 K, therefore being promising for its implementation in sensitive magnetometry and in quantum circuits as, for instance, Cooper pairs entanglers 5,6 . This device represents the first step towards the generation of highly-sensitive magnetometers, whose performance can be tuned in-situ by controlling the transparency of the contact between the superconducting probe and the weak-link.…”

“…Up to now, most of the related experimental works have been focused on the study of hybrid devices based on diffusive semiconductor nanowires 9,10 , normal metals 5,6 and ferromagnets 7 . Nevertheless, the structure flexibility and the reduced influence of disorder candidate S-2DEG systems as a promising platform to reach the complete understanding of these effects 11,12 .…”

“…The combination of ballistic two-dimensional-electrongases (2DEGs) and superconductors (S) may represent a key tool for the investigation of Majorana bound states 1-4 , the generation of solid-state entanglers 5,6 as well as spin triplet superconductivity 7,8 . Up to now, most of the related experimental works have been focused on the study of hybrid devices based on diffusive semiconductor nanowires 9,10 , normal metals 5,6 and ferromagnets 7 .…”