Photon-assisted-tunneling in a coupled double quantum dot under high microwave excitation powers

Abstract

ABSTRACT：We perform photon-assisted-tunneling (PAT) experiments on a GaAs double quantum dot device under high microwave excitation power. Photon-assisted absorption of up to 14 photons is observed, when electron temperature (>1K) are far above the lattice temperature. Signatures of Landau-Zener-Stückelberg (LZS) interference are found even in this non-equilibrium PAT spectrum. In addition, the charge state relaxation time ~8 measured in this out of thermal equilibrium double quantum dot is in agreement with other previous reports.2 Electro-statically-defined semiconductor quantum dot (QD) devices serve as an excellent platform of testing the properties of tunable two-level quantum systems as charge and spin qubits [1][2][3][4][5] . Among a variety of useful characterization and manipulation techniques, spectroscopy of microwave excited transport, known as photon assisted tunneling (PAT), are now used routinely to study the energy spectra and dynamic effects in QDs 6-8 .In this Letter, we report the study of a GaAs double quantum dot (DQD) device under high microwave power. In the presence of such strong excitation, the electron system is not in thermal equilibrium with the crystal lattice and thus they have different temperature. Thermal non-equilibrium effect in mesoscopic system has attracted increasing attention recently since the small scale of current electronic devices makes it possible for them to be driven out of thermal equilibrium using small power. We would like to see how various interesting dynamic effects (such as energy relaxation) of the two-level system change in thermal non-equilibrium cases where the electron temperature is significantly different from the lattice temperature.Our sample is fabricated on aheterostructure which contains a two-dimensional electron gas (2DEG) lying 100nm below the wafer surface with electron density 2.0 10 and mobility 6 10 · ⁄ . This sample is placed in a Helium-3 refrigerator 10 which could reach a base temperature of 240mK and hold on to it for 2-3 days until it has to be warmed up to 10K and cooled down again. Gates 1-6 shown in Fig.1 (a) form a typical DQD by depleting the electrons in 2DEG with Ti/Au top gates and gate 7 modulates the quantum point contact (QPC) channel to detect the charge state in the DQD by reading out the QPC differential current using a standard lock in measurement.(N, M) is used to represent the state with N electrons in the left dot and M electrons in the right dot. We estimate that there are about 10 electrons in each dot by measuring the charging energy. Of course, in principle, many-body states exist in this coupled DQD. However, we can still simply describe the system as a two-level one in which the topmost level of each dot is occupied by one electron and the others stay in their respective ground states.When the frequency of microwave photon matches the energy separation of the two-level system at zero DQD source-drain bias, electrons on the lower (upper) energy level can absorb (emit) one photon and jumped to the upper (low...

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