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Long Range Transport and Dark States in Quantum Dot Arrays Platero, Gloria


Superpositions of indirectly coupled states are possible in quantum mechanics even when the intermediate states are far apart in energy. This is achieved via higher-order transitions in which the energetically forbidden intermediate states are only virtually occupied. Interest in such long-range transitions has increased recently within the context of quantum information processing with the possibility of low dissipation transfer of quantum states or coherent manipulation of two distant qubits .The recently achieved control and tunability of triple quantum dots allow to investigate phenomena relying on quantum superpositions of distant states mediated by tunneling. Recent experiments in these devices show clear evidence of charge and spin electron exchange between the outermost dots [1, 2, 3]. In the present talk I will discuss configurations of triple dots in series where long range transfer and quantum interferences determine the transport properties. I will show that the destructive interference between two virtual paths can lead to current cancelation, what we termed superexchange blockade[4]. Finally I will address long-range transport and quantum interferences in ac driven triple dots where transitions between distant and detuned dots are mediated by the exchange of photons[5]. We propose the phase difference between the two ac voltages as an external parameter, which can be easily tuned to manipulate the current characteristics. For gate voltages in phase opposition we find quantum destructive interferences among long-range and direct photon- assisted transitions, analogous to the interferences in closed-loop undriven triple dots. As the voltages oscillate in phase, interferences between multiple virtual paths give rise to dark states. Those totally cancel the current, and could be experimentally resolved. References [1] M.Busletal.,Bipolarspinblockadeandcoherentstatesuperpositionsinatriplequantumdot,NatureNanotech.8,261(2013). [2] F.Braakmanetal.,Long-distancecoherentcouplinginaquantumdotarray,NatureNanotech,8,432(2013). [3] R.Sanchezetal.,Long-RangeSpinTransferinTripleQuantumDots,Phys.Rev.Lett.,112,176803(2014). [4] R.Sanchez,F.Gallego-MarcosandG.Platero,Superexchangeblockadeintriplequantumdots,Phys.Rev.B,89,16140(R)(2014). [5] F. Gallego-Marcos,R. Sanchez and G. Platero, Coupled Landau-Zener-Stuckelberg quantum dot interferometers, Phys. Rev. B, 93, 075424 (2016).

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