Surface-Acoustic-Wave-Induced Transport in a Double Quantum Dot

Abstract

We report on nonadiabatic transport through a double quantum dot under irradiation of surface acoustic waves generated on chip. At low excitation powers, absorption and emission of single and multiple phonons are observed. At higher power, sequential phonon assisted tunneling processes excite the double dot in a highly nonequilibrium state. The present system is attractive for studying electron-phonon interaction with piezoelectric coupling. DOI: 10.1103/PhysRevLett.96.136807 PACS numbers: 73.23.Hk, 63.20.Kr, 77.65.Dq Electron-phonon coupling often leads to dissipation and decoherence problems in nanoelectronic devices. The decoherence in a tunable two-level quantum system (qubit), such as a double quantum dot (DQD) [1], is of particular interest in the recent light of quantum computation and information [2]. It was found that piezoelectric coupling to acoustic phonons is the dominant mechanism for inelastic transition between two charge states in a DQD [3], as confirmed by theory [4]. In analogy to quantum states in natural atoms-which dominantly couple to and are successfully controlled by photons-the electronic states in solid state systems may be controlled by phonons, taking advantage of the strong electron-phonon coupling.Because of the piezoelectric coupling in GaAs, surface acoustic waves (SAWs) can be generated by applying a microwave signal to an interdigital transducer (IDT) [5]. The accompanying propagating and oscillating potential has been used in several experiments to transport photogenerated electrons and holes in so-called ''dynamical quantum dots '' [6]. In those experiments, however, the SAWs give rise to an adiabatic change of the electronic states, where the carriers remain in an eigenstate of the temporal potential.In this Letter, we present nonadiabatic transitions in a lithographically defined DQD under irradiation of coherent SAWs. We observe resonant phonon assisted tunneling, where transport is well described by considering absorption and emission of one or multiple phonons during the tunneling process [7]. The present results unambiguously indicate a finite contribution of SAWs to the bosonic environment of a quantum two-level system formed by a DQD. Moreover, these transport measurements allow us to determine extremely small amplitudes of the local piezoelectric potential.

Universal Quantum Transducers Based on Surface Acoustic Waves

“…The electron's charge e couples to the piezoelectric potential; the deformation coupling is much smaller than the piezoelectric coupling and can therefore safely be neglected [47]. Since the quantum dot is small compared to the SAW wavelength, we neglect potential effects coming from the structure making up the dots (heterostructure and metallic gates); for a detailed discussion, see Appendix I.…”

“…Here, we assume λ ≈ 2l, such that the geometrical factor sin ðπl=λÞ ≈ 1 [47]. In principle, the coupling strength g ch could be further enhanced by additionally depositing a strongly piezoelectric material such as LiNbO 3 on the GaAs substrate.…”

Pulse-induced acoustoelectric vibrations in surface-gated GaAs-based quantum devices

“…In a double-quantum-dot system, this could lead to inelastic tunneling between the adjacent dots. 16 Figure 2͑a͒ also shows the ability of the surface acoustic wave modes to propagate for at least 4 m along the surface with no decay in amplitude. The mentioned 4 m is only a limit of the computational domain, and we would expect the induced surface acoustic wave to propagate over much longer distances.…”

Phonon-induced relaxation of a two-state system in solids

“…2 to the study of two-phonon Raman processes in double-well structures. [3][4][5][6][7][8] Such processes can dominate relaxation at higher temperatures. [9][10][11] We will show that in the temperature range bounded by the level splitting from below and by the Debye temperature from above, the rate of the Raman process for a biased rigid double well is given by a universal expression, very much like the rate of the direct one-phonon process.…”