Two-path transport measurements on a triple quantum dot

Abstract

As an advanced quantum system, a three terminal triple quantum dot with one lead attached to each dot allows us to simultaneously measure a transport along two different paths. Quadruple points with all three dots in resonance are prepared and investigated for different electron numbers in the individual quantum dots including one dot with only one or two electrons. DOI: 10.1103/PhysRevB.77.193306 PACS number͑s͒: 73.21.La, 73.23.Hk, 73.63.Kv The spin of electrons on a quantum dot is proposed as a realization of a qubit that is needed for quantum computation. 1 Therefore, quantum dots, the so-called artificial atoms, have been intensively investigated in recent years. 2 Next to single quantum dots, two coupled quantum dots ͑artificial molecules͒ have gained broad interest. 3 Coupling phenomena have been investigated in devices with parallel 4,5 as well as with serial 6-9 configurations. The ongoing technological progress has allowed the fabrication of more and more complicated setups, including charge detection with quantum point contacts ͑QPCs͒. 10,11 Recently, the technological and scientific preconditions have reached a level that allows one to go beyond single and coupled qubits. An exciting field of research is being entered: the investigation of triple quantum dots.Next to fundamental physics, the research on triple quantum dots is motivated by the fact that a triple quantum dot is the smallest system, with quantum dots being part of a qubit chain. However, despite this importance for quantum computation and further interesting theoretical predictions, 12-15 triple quantum dots have almost not been investigated so far ͑except for some basic experiments in the early 1990s 16,17 ͒ due to experimental difficulties. Now that researchers have started to overcome these difficulties, the intensive investigation of triple dots has begun with three recently published experiments. Vidan et al. 18 investigated a serial double quantum dot with a side coupled third dot as a quantum box. Gaudreau et al. 19 observed charge rearrangements on a ringlike triple quantum dot in a system that was originally designed for double quantum dots. Schröer et al. 20 created a system with three dots in a row.In this Brief Report, we present a different geometry for a lateral triple quantum dot. We created a starlike system with each dot placed next to the other two. In contrast to the formerly published works, we have three leads connected to our system, one for each quantum dot. Thus, we can simultaneously measure the transport via different paths with only two dots per path. With this setup, transitions from configurations of two dots in resonance ͑triple points͒ to configurations of all three dots in resonance ͑quadruple points͒ can be studied in transport in order to understand the formation of triple quantum dot states.To enable charge detection, we extend our device by a QPC, making the setup more flexible. With this variety of features, we decided to use an atomic force microscope ͑AFM͒ to build this unique setup, as this te...

Capacitively coupled double quantum dot system in the Kondo regime

“…[9][10][11] This interaction is responsible for several fascinating phenomena, e.g., Coulomb blockade, 11,12 and Kondo effect, 7,13,14 leading to characteristic behavior of the thermodynamical and transport properties, which depend drastically on the number of QDs, as well as on their topological configuration in the structure. In recent years, strong on-site interaction in double 13,[15][16][17][18][19][20][21][22][23][24] and triple [25][26][27][28][29][30][31][32] QD (DQD and TQD) structures have received a great deal of attention when in the Kondo regime. However, on-site electron-electron interaction does not exhaust all the possibilities in multiple QD structures, as electrons can, due to their proximity, interact with each other, even when located in different QDs.…”

Noninvasive detection of molecular bonds in quantum dots

“…The device is described in detail in Ref. 15. Figure 1 shows a charging diagram of the triple dot device as a function of the voltages applied to gates G3 and G1.…”

A few-electron quadruple quantum dot in a closed loop

“…Up to now, only three dots in series have been demonstrated to be tunable [9,10] in the few-electron regime. A triple quantum dot geometry in a star-like configuration has been demonstrated, but the geometry did not allow tunneling between all close-by dots and the few-electron regime was not reached [11].Here we present the first step towards the transfer of a single electron spin on a closed path using a series of quantum dots in a square-like geometry. We demonstrate that we are able to set the system in the few-electron regime using charge detection techniques and therefore to remove the other electrons along the path.…”