Three-terminal superconductor (S) - normal metal (N) - superconductor (S) Josephson junctions are investigated. In a geometry where a T-shape normal metal is connected to three superconducting reservoirs, new sub-gap structures appear in the differen
tial resistance for specific combinations of the superconductor chemical potentials. Those correspond to a correlated motion of Cooper pairs within the device that persist well above the Thouless energy and is consistent with the prediction of quartets formed by two entangled Cooper pairs. A simplified nonequilibrium Keldysh Greens function calculation is presented that supports this interpretation.
We have implemented a new experimental set-up for precise measurements of current fluctuations in three-terminal devices. The system operates at very low temperatures (30 mK) and is equipped with three SQUIDs as low noise current amplifiers. A SQUID
input coil is connected to each terminal of a sample allowing the acquisition of time-dependent current everywhere in the circuit. From these traces, we can measure the current mean value, the noise and cross-correlations between different branches of a device. In this paper we present calibration results of noise and cross-correlations obtained using low impedance macroscopic resistors. From these results we can extract the noise level of the set-up and show that there are no intrinsic correlations due to the measurement scheme. We also studied noise and correlations as a function of a DC current and estimated the electronic temperature of various macroscopic resistors.
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 noi
se 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.
We present current noise measurements in a long diffusive superconductor-normal-metal-superconductor junction in the low voltage regime, in which transport can be partially described in terms of coherent multiple Andreev reflections. We show that, wh
en decreasing voltage, the current noise exhibits a strong divergence together with a broad peak. We ascribe this peak to the mixing between the ac- Josephson current and the noise of the junction itself. We show that the junction noise corresponds to the thermal noise of a nonlinear resistor 4kBT=R with R V = I V and no adjustable parameters.
