Hasler T., Jung M., Ranjan V., Puebla-Hellmann G., Wallraff A., Schoenenberger C. (2015), Shot Noise of a Quantum Dot Measured with Gigahertz Impedance Matching, in PHYSICAL REVIEW APPLIED
, 4(5), 054002.
One of the present day challenges in quantum electronics is to create entangled electron pairs with high efficiency and distribute the entanglement over long distances with high fidelity. Whereas schemes for the local generation of entangled electron pairs have been demonstrated, for example using Cooper-pairs or double quantum dots, the distribution remains a challenge. As compared to photons the distribution is much harder for electrons in the solid-state, because unlike photons the electrons in devices are strongly interacting and part of a many-body system, the Fermi sea. Until today, no transport experiment could demonstrate electron entanglement via a non-local measurement. Inspired by the Bell-test with photons, where coincident counts at two distant detectors are analyzed, theorists have proposed to use noise correlation experiments to mimic coincidence counts and to construct a Bell inequality. In a certain parameter range, a Bell-test based on shot-noise correlation is indeed possible. However, noise may be suppressed due to many-body screening effects. Due to the requirement to measure noise with a resolution of mK (milli-Kelvin) in devices with high impedances, typically larger than 100 kOhm, one has to measure at high frequencies in the 100 MHz to 10 GHz window to overcome spurious low frequency 1/f noise caused by the trapping and detrapping of charge in oxide layers. Cryogenic amplifiers have noise temperatures of a few Kelvins. One therefore has to average over a very long time to achieved the required accuracy. Here, we propose to build an unique cryogenic systems for noise-correlation experiments implementing parametric amplifiers which can operate at the quantum limit and dedicated impedance matching circuits. This will provide enough resolution to make possible the measurement of entanglement by non-local noise correlation experiments not only using second-order moments, but even higher ones.