Individually addressable double quantum dots formed with nanowire polytypes and identified by epitaxial markers

Abstract

Double quantum dots (DQDs) hold great promise as building blocks for quantum technology as they allow for two electronic states to coherently couple. Defining QDs with materials rather than using electrostatic gating allows for QDs with a hard-wall confinement potential and more robust charge and spin states. An unresolved problem is how to individually address these quantum dots, which is necessary for controlling quantum states. We here report the fabrication of double quantum dot devices defined by the conduction band edge offset at the interface of the wurtzite and zinc blende crystal phases of InAs in nanowires. By using sacrifical epitaxial GaSb markers selectively forming on one crystal phase, we are able to precisely align gate electrodes allowing us to probe and control each QD independently. We hence observe textbook-like charge stability diagrams, a discrete energy spectrum and electron numbers consistent with theoretical estimates and investigate the tunability of the devices, finding that changing the electron number can be used to tune the tunnel barrier as expected by simple band diagram arguments.When electrons are spatially confined in semiconductor quantum dots (QDs), they form bound states with discrete energy levels. These systems have drawn much attention both experimentally and theoretically [1,2] as they form atom-like structures in solid-state. One system of particular importance is the double quantum dot (DQD) where two discrete electronic states couple coherently, making it the building block of charge and spin qubits [1][2][3][4][5][6]. QDs are also elemental in other semiconductor quantum systems that are promising for use in quantum computers and quantum systems in general [4,5,7], such as Majorana fermions [8][9][10][11]. QDs are commonly defined by gate depletion [2,5,12], but progress has been made in material-defined QDs as well [13][14][15]. The material-defined approach allows for more well-defined features and less coupling to external noise. In this letter, we utilize recently developed InAs polytype bandgap engineering [15][16][17] to define DQDs with a hard-wall potential. With epitaxial markers, we gain control of the individual dots and, demonstrate the honeycomb-shaped charge stability diagrams of material-defined DQDs and the robustness of the system with a wide range of electron populations.The most common approach to forming quantum dots for transport experiments is to start from a material system that is already structurally confined in one or two dimensions and use electrostatic gating to confine the remaining dimensions.Examples here include two-dimensional electron gases [2,5], one-dimensional carbon nanotubes and semiconductor nanowires [12]. These partially gate-defined QDs have a smoothly changing confinement potential and hence their size *

Efficient and continuous microwave photoconversion in hybrid cavity-semiconductor nanowire double quantum dot diodes

“…Our photodiode device contains a crystal phase-defined double quantum dot (DQD) in a semiconductor InAs nanowire 20 embedded in a superconducting coplanar microwave resonator (Fig. 1 ).…”

“… 34 and the integration of the DQD to the device was done by following the recipe of ref. 20 . Gold pads were used as interconnects to obtain conducting contacts between the resonator and the DQD lines.…”

“…After fabricating the resonator, the process continued as in ref. 20 : InAs nanowires were transferred on the designated spots with pre-patterned alignment marks by pick and drop method. In the next step, electron-beam lithography was opted to connect one side of nanowire with the microwave resonator that serves as source reservoir and the other end of nanowire is connected to a metallic DC pad, which acts as drain reservoir.…”

Quantum Fokker-Planck master equation for continuous feedback control

“…A promising platform for exploring feedback control within quantum thermodynamics is solid state electronic systems [50], ranging from semiconductor quantum dots [51] to superconducting qubits [52]. Key features in these systems are large and fast tunability of system properties [53][54][55] and time resolved measurements [56,57]. Moreover, both discrete [29,58,59] and continuous [6,27] feedback protocols have been demonstrated experimentally.…”

Gate control, g-factors and spin orbit energy of p-type GaSb nanowire quantum dot devices

“…Consequently, an important step toward the realization of GaSb nanowire based spintronic devices is the development of device architectures allowing the formation and characterization of small QDs. For the more common nanowire material InAs the development of local bottom-gates [14] and later epitaxially defined InP-InAs-InP [15,16] as well as Wz-Zb-Wz polytype structures [17,18] have enabled small, tunable and flexible high quality QD and serial double quantum dot (DQD) devices, which are now widely used for various transport studies. For GaSb nanowires, epitaxially defined QD structures are not yet experimentally available and the design of flexible, local gate architectures is challenging for Schottky contacted nanowires.…”