Special CPM Seminar

Transport signatures of long-range nuclear-spin coherence in a quantum-dot spin valve

Stefano Chesi

CSRC, Beijing, China

We have analyzed the efficient transfer of angular momentum into the nuclear bath of a quantum-dot spin valve. Such transport setup is close to several recent experimental realizations, based on self-assembled quantum dots or quantum dots in nanowires and carbon nanotubes. We show how nuclear-spin coherence can be detected through transport signatures associated to the quantum dot hyperfine interaction. Long-range nuclear-spin coherence is established through electron transport and can induce a strong enhancement of the spin-flip transition rates induced by the hyperfine interaction. Under a finite voltage bias, such enhancement is revealed by an intense current burst analogous to superradiant light emission while fast local dephasing of the nuclear spins destroys the effect and leads to an incoherent evolution analogous to spontaneous emission. Through a combination of simple rate equations and a more general master equation we have characterized the two limiting regimes and the crossover between them. As the strongest coherent enhancement is achieved with uniform hyperfine couplings, we propose realistic strategies (based on isotopic modulation and wavefunction engineering in core-shell nanowires) to realize such analytically solvable �~@~\box-model" of hyperfine couplings.