Asymmetric quantum shot noise in magnon transport

Nakata, Koki   ; Onuma, Yuichi*; Matsuo, Mamoru*

We study a frequency-dependent noise-to-current ratio for asymmetric, symmetric, and noncommutative current noise in a ferromagnetic insulating junction, and extract quantum-mechanical properties of magnon transport at low temperatures. We demonstrate that the noncommutative noise, which vanishes in the dc limit (i.e., a classical regime), increases monotonically as a function of frequency, and show that the noncommutative noise associated directly with quantum fluctuations of magnon currents breaks through the classical upper limit determined by the symmetric noise and realizes asymmetric quantum shot noise. Finally, we show that our theoretical predictions are within experimental reach with current device and measurement schemes while exploiting low temperatures. Our work provides a platform toward experimental access to quantum fluctuations of magnon currents.