Entanglement witnessing and quantum cryptography with nonideal ferromagnetic detectors
Waldemar Kłobus, Andrzej Grudka, A. Baumgärtner, Damian Tomaszewski, Christian Schönenberger, J. Martinek · Physical Review B · 2014
We investigate theoretically the use of nonideal ferromagnetic contacts as a means to detect quantum entanglement of electron spins in transport experiments. We use a designated entanglement witness and find a minimal spin polarization of $\ensuremath{\eta}>1/\sqrt{3}\ensuremath{\approx}58%$ required to demonstrate spin entanglement. This is significantly less stringent than the ubiquitous tests of Bell's inequality with $\ensuremath{\eta}>1/\sqrt[4]{2}\ensuremath{\approx}84%$. In addition, we discuss the impact of decoherence and noise on entanglement detection and apply the presented framework to a simple quantum cryptography protocol. Our results are directly applicable to a large variety of experiments.