NanoTech2022_10

Quantum bit

• state can be visualized by a point inside a sphare.
• can have two states.
• allows quantum parallelism due to fast readout.
• is a two level quantum system.

Universal quantum computer

• could solve our computational problems exponentially faster.
• requires only a single type of two qubit gate.
• allows to read out the superposition of the qubit states.
• is very fregile due to the slow operational speed.

Spin qubit

• is a concept where qubit is generalized with a spin degree of freedom.
• is based on GMR effect and the long spin relaxation length.
• has two states depending on the orbital degree of freedom.
• operates with the 1/2 spin state of a trapped electron.

Memristors

• are two level systems with different resistance values.
• have larger unit size than Flash memories, which limits their application.
• have multiply resistance values thus they could overperform qubits.
• are ideal to model neural networks at the hardware level.

Giant magnetoresistant

• requires a junction with two normal and one ferromagnetic layers.
• requires that electrons travel ballisticly through the device.
• requires spin conservation in the middle layer of the device.
• shows a resistance increase as ferromagnetic layers switch to parallel orientation.

Non-local spin measurement

• allows to detect spin relaxation length based on Hall-effect.
• requires current driving to minimize spin relaxation.
• allows to measure spin signal separating it from the path of the electric current.
• does not allow to determine the spin diffusion length.

Spin relaxation

• can take place at scattering centers, due to Lorentz-force.
• in case of broken inversion symmetry is reduced for longer mean free path.
• is not sensitive to the presence of magnetic impurities.
• can take place in the presence of spin-orbit interaction and scatterings.

Spin transfer torque

• allows to rotate the magnetization direction with minimizing spin relaxation.
• is based on Dyakunov - Perel mechanism.
• induces resitance changes thanks to external magnetic field.
• allows to switch ferromagnetic layers by electric current.