Far-infrared magnetospectroscopy of polaron states in self-assembled InAs/GaAs quantum dots

Polaron resonances in two vertically stacked quantum dots

“…In QDs, the carrier spectrum is discrete, while the relatively weak carrier localization limits the effectively coupled LO phonons to the nearly dispersionless zone-center part of their spectrum. As a result, the system is in the strong coupling regime and the polaron states are manifested in the form of pronounced resonances whenever one excited state spectrally crosses a LO-phonon replica of another state [3][4][5] . The width of the resonances provides a natural quantitative measure of the strength of the carrier-phonon coupling.…”

“…Recently, the spectrum of such a system was mapped out by combined spectroscopy techniques and successfully modeled using an 8-band k·p theory in the envelope-function approximation 18 . The electric-field tunability of energy levels in such systems might allow one to study the polaron resonances as a function of the electric field by matching various energy shells of the two dots, which offers much more flexibility in comparison to the single-QD studies, where only limited tunability by magnetic field is available 3,4 .…”

Fast Control of Quantum States in Quantum Dots: Limits due to Decoherence

“…The interaction with the quasicontinuum of lattice degrees of freedom (phonons) constitutes an inherent feature of these nanometer-size systems and cannot be neglected in any realistic modeling of QD properties, especially when the coherence of confined carriers is of importance. The understanding of the decisive role played by the QD coupling to lattice modes has increased recently due to both experimental and theoretical study (spectrum reconstruction [1][2][3][4], relaxation [5][6][7][8][9][10], phonon replicas and phonon-assisted transitions [11][12][13][14][15][16], phonon-induced pure dephasing upon ultrafast excitation [17][18][19][20][21][22]). The phonon-induced decoherence seems to be crucial for any quantum information processing application and for any nanotechnological device relying on quantum coherence of confined carriers [23,24].…”

“…There are three major mechanisms of carrier-phonon interaction [25]: (1) Coulomb interaction with the lattice polarization induced by the relative shift of the positive and negative sub-lattices of the polar compound, described upon quantization by longitudinal optical (LO) phonons; (2) deformation potential coupling describing the band shifts due to lattice compression, i.e. longitudinal acoustical (LA) phonons; (3) Coulomb interaction with piezoelectric field generated by shear crystal deformation (transversal acoustical, TA, phonons).…”

“…The time evolution of the dressing process is described by the inverse Fourier transform of the correlation function given by (2). Taking into account that for ω in the energy sector of exciton (of order of eV) ω ≫ k B T , one has…”