Photon-assisted tunneling through a quantum dot

Abstract

We study single-electron tunneling in a two-junction device in the presence of microwave radiation. We introduce a model for numerical simulations that extends the Tien-Gordon theory for photon-assisted tunneling to encompass correlated single-electron tunneling. We predict sharp current jumps which reflect the discrete photon energy h f, and a zero-bias current whose sign changes when an electron is added to the central island of the device. Measurements on split-gate quantum dots show microwave-induced features that are in good agreement with the model. An oscillating potential with frequency f changes the energy F. of an electron state into a set of energies E+nhf with n=0,~1,~2, . . . . These so-called sideband energies can lead to electron tunneling that involves the emission (n&0) and absorption (n)0) of photons. The formation of sidebands has been important for many time-dependent transport studies addressing issues such as photon-assisted tunneling of quasiparticles in superconducting junctions, the tunneling time, and time-dependent resonant tunneling. Recent theoretical work has begun to focus on the effects of an oscillating potential on transport through small capacitance devices where the charging energy regulates the tunnel processes. For instance, Bruder and Schoeller have calculated the photoresponse of a two-level system. However, little theoretical work exists on realistic systems, e.g. , quantum dots with many quantum levels, and no experiments have been reported except at very low frequencies. "In this paper, we present numerical simulations and experiments on photon-assisted tunneling through a quantum dot. We assume a continuous single-particle density of states, i.e. , a metallic system with an equivalent single electron circuit shown in the inset of Fig. 1 . Our model extends theTien-Gordon theory' to include the correlated tunneling of single electrons through a two-junction device. This model predicts discrete photon features, and is in agreement with measurements on split-gate quantum dot devices irradiated by 19-GHz microwaves.We model the microwaves as an oscillating potential V cos(2mft) of the central island relative to the source and drain leads. To allow for an asymmetry in the ac coupling, we model the microwave amplitude by two parameters a; =eV;/h f, i =s,d where V, and Vd are the ac voltage drops across the source and drain junctions. Analogous to the Tien-Gordon description, we write the tunnel rate I; in the presence of microwaves in terms of the rate 1; without microwaves as

Photon Assisted Tunneling in Quantum Dots

“…Structure due to photon energies below this value is washed out by the thermal energy k B T . The frequency scaling firmly establishes PAT as the transport mechanism [9,[11][12][13][14]. The observation that the sidebands move linearly with frequency, while the ground and excited state resonances stay fixed, supports our identification of the different peaks.…”

“…In 1993 PAT features were seen in the current-voltage characteristics of a GaAs/AlGaAs superlattice under THz irradiation from a free-electron laser [11]. Starting in 1994, PAT was also found in experiments on single-electron transport through semiconductor quantum dots [12][13][14][15][16]. The quantum dots in Ref.…”

“…However, this is only true when the ac voltage drop is the same for both barriers. When the ac voltage drops across the two barriers are unequal, the dot acts as an electron pump [3,12,27]. The resulting pumped current makes the resonances discussed above less clear.…”

“…A direct inclusion of the Tien and Gordon equations [9] in a master equation that takes into account Coulomb blockade [22] can be made by writing the tunnel rate through each barrier in the presence of microwaves Γ(E) in terms of the rates without microwaves Γ(E) [12]:…”

Charge transport through open driven two-level systems with dissipation

“…When the time-dependence is slow, this can give rise to a variety of adiabatic phenomena such as charge pumping 10,11,12,13,14,15,16,17,18,19 , adiabatic control of state vectors 20,21 , or operations relevant for quantum information processing in a condensedmatter setting 22,23,24,25,26,27,28 . Different physics occurs in the high frequency regime where monochromatic timevariation induces photo-excitations, such as for coupling of AC fields to quantum dots 29,30,31,32,33,34 , which has been tested experimentally 35,36,37,38,39,40 recently.…”