1# Copyright 2011-2013 Kwant authors. 

2# 

3# This file is part of Kwant. It is subject to the license terms in the file 

4# LICENSE.rst found in the top-level directory of this distribution and at 

5# https://kwant-project.org/license. A list of Kwant authors can be found in 

6# the file AUTHORS.rst at the top-level directory of this distribution and at 

7# https://kwant-project.org/authors. 

8 

9import numpy as np 

10from ..solvers.common import SMatrix 

11 

12__all__ = ['two_terminal_shotnoise'] 

13 

14 

15def two_terminal_shotnoise(smatrix): 

16 r"""Compute the shot-noise in a two-terminal setup. 

17 

18 In a two terminal system the shot noise is given by `tr((1 - t*t^\dagger) * 

19 t*t^\dagger)`. 

20 

21 Parameters 

22 ---------- 

23 smatrix : `~kwant.solvers.common.SMatrix` instance 

24 A two terminal scattering matrix. 

25 

26 Returns 

27 ------- 

28 noise : float 

29 Shot noise measured in noise quanta `2 e^3 |V| / pi hbar`. 

30 """ 

31 

32 if not isinstance(smatrix, SMatrix): 32 ↛ 33line 32 didn't jump to line 33, because the condition on line 32 was never true

33 raise NotImplementedError("Noise expressions in terms of Green's " 

34 "functions are not implemented.") 

35 

36 if len(smatrix.lead_info) != 2: 

37 raise ValueError("Only works for two-terminal systems!") 

38 

39 t = smatrix.submatrix(smatrix.out_leads[0], smatrix.in_leads[0]) 

40 ttdag = np.dot(t, t.conj().T) 

41 return np.trace(ttdag - np.dot(ttdag, ttdag)).real 

42 

43 

44# A general multi-terminal routine for noise would need to also have the 

45# voltages at various leads as input. (See 

46# https://arxiv.org/abs/cond-mat/9910158) It could still be based on 

47# smatrix._a_ttdagger_a_inv, i.e. be also valid also for self-energy leads, 

48# provided that only true transmission blocks are used. As long as nobody needs 

49# it though, it does make little sense to make such a routine.