Physics for Electronics Engineering: Unit II: Electrical and Magnetic Properties of Materials

Quantum Interference Effect

Quantum Superposition, Applications

It is a fundamental principle of quantum mechanics. It states that much like waves in classical physics, any two (or more) quantum states can be added together ("superposed") and the result will be another valid quantum state.

Quantum Interference Effect

Quantum superposition

It is a fundamental principle of quantum mechanics. It states that much like waves in classical physics, any two (or more) quantum states can be added together ("superposed") and the result will be another valid quantum state. (Fig. 2.31)

Magnetic fields can produce and control interference effects between the electrons in solids. In order to observe interference


effects between different electron waves, their phase has to be maintained.

The phase coherence length Lφ is the distance travelled by an electron without changing its phase. The phase of an electron wave is generally destroyed when electrons interact inelastically with defects in the lattice.

In general, ballistic electrons with a mean free path le much larger than sample dimensions L, (i.e. le >> L,) travel through the lattice without scattering. Therefore they show interference effects.

Applications of Quantum Interference Effect

Quantum interference effect is being applied in a growing number of applications, such as the

i. Superconducting Quantum Interference Device (SQUID).

ii. quantum cryptography

iii. quantum computing and quantum interference transistor.

Physics for Electronics Engineering: Unit II: Electrical and Magnetic Properties of Materials : Tag: : Quantum Superposition, Applications - Quantum Interference Effect