Week 11: The info-battery and Landauer erasure

The info-battery: energy from information (Datta Ch. 16, Fig. 16.3; Landauer's principle)

N localized spins sit in a perfect anti-parallel spin valve: the source only exchanges up-spin electrons (u), the drain only down-spin electrons (d). The exchange "reaction" u + D ⇔ U + d flips spins. Starting from the known all-up state (S = 0), the spins randomize while pushing electrons through an external load: the open-circuit voltage is Δμ = kT ln(P_U/P_D) (Eq. 16.10). The spins' energy never changes: the work comes from the surroundings, paid for by the entropy increase, at most TΔS = NkT ln 2 (Eqs. 16.5, 16.11).

Load resistance (relative to the device) Erasure overdrive η = (q·V_battery − Δμ)/kT

Fraction of up spins P_U–

Open circuit Δμ/kT = ln(P_U/P_D) · terminal qV/kT–

Entropy S/Nk (max ln 2 = 0.693)–

Energy to the load E/NkT (max ln 2)–