Optically programmable excitonic traps

Abstract

With atomic systems, optically programmed trapping potentials have led to remarkable progress in quantum optics and quantum information science. Programmable trapping potentials could have a similar impact on studies of semiconductor quasi-particles, particularly excitons. However, engineering such potentials inside a semiconductor heterostructure remains an outstanding challenge and optical techniques have not yet achieved a high degree of control. Here, we synthesize optically programmable trapping potentials for indirect excitons of bilayer heterostructures. Our approach relies on the injection and spatial patterning of charges trapped in a field-effect device. We thereby imprint in-situ and on-demand electrostatic traps into which we optically inject cold and dense ensembles of excitons. This technique creates new opportunities to improve state-of-the-art technologies for the study of collective quantum behavior of excitons and also for the functionalisation of emerging exciton-based opto-electronic circuits.

Transport of indirect excitons in a potential energy gradient

“…This pattern is similar to the inner ring studied previously 4,6,8,10,21,22 . The inner ring was explained in terms of exciton transport and cooling: optical excitation heats the exciton gas, excitons cool towards the lattice temperature as they travel away from the excitation spot, the cooling results in an increase in the occupation of the low-energy optically active exciton states and, as a result, the appearance of an emission ring around the excitation spot 4,6,8,10,22 . Figure 1d presents a numerical simulation of the potential energy profile for indirect excitons edF z for constant voltage V e = −3 V applied to the top electrode shown in Fig.…”

“…Furthermore, indirect excitons have a built-in dipole moment ed, where d is close to the distance between the quantum well (QW) centers that allows their energy to be controlled by voltage: an electric field F z perpendicular to the QW plane results in the exciton energy shift E = edF z 11 . These properties allow studying transport of indirect excitons in electrostatically created in-plane potential landscapes E(x, y) = edF z (x, y).Exciton transport was studied in various electrostatic potential landscapes including circuit devices 12-14 , traps 15 , lattices 16,17 , moving lattices -conveyerscreated by a set of ac voltages 18 , and narrow channels 14,19,20 .Several exciton transport phenomena have been observed, including the inner ring in emission patterns 4,6,8,10,21,22 , transistor effect for excitons [12][13][14] , localization-delocalization transition in random potentials 4,6,8 and in lattices 16,17 , and dynamical localization-delocalization transition in conveyers 18 . Exciton transport was also studied in potential energy gradients created by voltage gradients in electrodes 1,7 .…”

“…The spatial separation allows one to control the overlap of electron and hole wavefunctions and engineer structures with lifetimes of indirect excitons orders of magnitude longer than those of direct excitons. Long lifetimes of the indirect excitons allow them to travel over large distances before recombination [1][2][3][4][5][6][7][8][9][10] . Furthermore, indirect excitons have a built-in dipole moment ed, where d is close to the distance between the quantum well (QW) centers that allows their energy to be controlled by voltage: an electric field F z perpendicular to the QW plane results in the exciton energy shift E = edF z 11 .…”

“…Several exciton transport phenomena have been observed, including the inner ring in emission patterns 4,6,8,10,21,22 , transistor effect for excitons [12][13][14] , localization-delocalization transition in random potentials 4,6,8 and in lattices 16,17 , and dynamical localization-delocalization transition in conveyers 18 . Exciton transport was also studied in potential energy gradients created by voltage gradients in electrodes 1,7 .…”

Pattern formation in the exciton inner ring

“…10,13,24,27 A set of exciton transport phenomena was observed, including the transistor effect for excitons, 14,15,19,21 localizationdelocalization transition in random potentials 7,9,10,13,17,22 and in static and moving lattices, 18,23,29 and the inner ring in emission patterns. 7,9,17,18,26,28,29,32 The studies of the latter form the subject of this work.…”