Magnetic field sensor

1. A device for sensing a magnetic field comprising:

first, second and third leads; and

a junction connected with the first, second and third leads; wherein

the junction and the leads are arranged in a plane and the junction is configured to exhibit quantum confinement in a direction perpendicular to the plane, wherein the first lead is arranged on one side of the junction and the second and third leads are arranged on an opposite side of the junction.

2. The device as in claim 1 , wherein the first lead is elongated along a longitudinal axis and, when charge carriers flow from the first lead into the junction, the charge carriers flow substantially parallel to the longitudinal axis.

3. The device as in claim 1 , wherein the first lead is configured to exhibit quantum confinement in a lateral direction so as to provide a quantum wire.

4. The device as in claim 1 , further comprising a gate structure configured to provide an electrostatic lens for focussing charge carriers in the first lead so as to limit the angle of spread of charge carriers entering the junction.

5. The device as in claim 1 , wherein a portion of the first lead which is configured to limit angle of spread of charge carriers entering the junction is adjacent to the junction.

6. The device as in claim 1 , wherein the junction comprises non-ferromagnetic and/or semiconducting material.

7. The device as in claim 1 , wherein the junction has an area equal to or less than about 1000 nm 2 .