Phonon-Mediated Nonequilibrium Interaction between Nanoscale Devices

Abstract

Interactions between mesoscopic devices induced by interface acoustic phonons propagating in the plane of a two-dimensional electron system (2DES) are investigated by phonon-spectroscopy. In our experiments ballistic electrons injected from a biased quantum point contact emit phonons and a portion of them are reabsorbed exciting electrons in a nearby degenerate 2DES. We perform energy spectroscopy on these excited electrons employing a tunable electrostatic barrier in an electrically separate and unbiased detector circuit. The transferred energy is found to be bounded by a maximum value corresponding to Fermi-level electrons excited and back-scattered by absorbing interface phonons. Our results imply that phonon-mediated interaction plays an important role for the decoherence of solid-state-based quantum circuits.PACS numbers: 68.65.-k,73.23.-b,73.63.-b,03.67.-a Nanoscale electronic circuits dominate present information technologies. Based on their coherent dynamics they are also considered as candidates for future quantum information processing [1,2]. Therefore, it is important to understand and control decoherence-inducing processes, such as the non-equilibrium back-action of a biased quantum point contact (QPC), widely used as single electron detector. However, the details of the relevant back-action mechanisms are not yet understood and a matter of ongoing investigations [3,4,5,6,7].Phonon-induced currents in a two-dimensional electron system (2DES) have been evidenced in thermopower experiments [8,9] and also directly imaged with ballistically injected phonons [10]. In our experiments we employ a spectrometer, conceptually similar to a so-called lateral tunneling hot-electron amplifier [11], to analyse the energy of excited electrons in a 2DES and to study energy transfer mechanisms between mesoscopic circuits.The inset of Fig. 1a sketches the calibration procedure of the energetic height E Ba of an analyzer barrier Ba to be employed for quantitative energy spectroscopy. Hot electrons, injected across a barrier Bi into a degenerate Fermi-sea of cold electrons, move ballistically with an excess kinetic energy of E kin − E F ≤ |eV SD | towards Ba. As long as E Ba < E kin some of these electrons pass Ba resulting in an analyzer current I a , while I a vanishes for E Ba > E kin . The onset of I a (V SD ) at E Ba = E F + |eV SD | serves as calibration of the barrier height E Ba . The result of such a calibration measurement is plotted in Fig. 1a displaying I a (gray scale and contour lines) as a function of the gate voltage V Ba and the bias V SD . The ballistic motion of the electrons insures a straight line of current onset (purple), converting the gate voltage V Ba (bottom scale of Fig. 1a) to the barrier height E Ba (top scale). For E Ba < E F a calibration is obtained by utilizing quantization of the electronic density of states into Landau levels with well known energies in a perpendicular magnetic field [12,13]. Note that one calibration point, namely for E Ba = E F , is in addition obtained by applyin...

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