A few-electron quadruple quantum dot in a closed loop

Abstract

We report the realization of a quadruple quantum dot device in a square-like configuration where a single electron can be transferred on a closed path free of other electrons. By studying the stability diagrams of this system, we demonstrate that we are able to reach the few-electron regime and to control the electronic population of each quantum dot with gate voltages. This allows us to control the transfer of a single electron on a closed path inside the quadruple dot system. This work opens the route towards electron spin manipulation using spin-orbit interaction by moving an electron on complex paths free of electrons. PACS numbers:Controlling the path of a single electron in semiconducting nanostructures is an interesting tool in the context of spin qubits systems. In particular, it opens the route towards the transport of quantum information on a chip and represents a potential strategy to scale up the number of spin qubits in interaction [1]. In addition, in presence of spin-orbit interaction, it represents an interesting way to manipulate coherently the spin of a single electron [2][3][4]. Recently, fast and efficient single electron transport could be obtained by assisting the transport through a 1D-channel electrostatically defined with surface acoustic waves on AlGaAs heterostructures [5,6]. Nevertheless, such a technique is restricted to displacements on a straight line. To perform more complex displacements, engineering the path of the electron with series of quantum dots is a promising alternative. In this context, it has been demonstrated that topological spin manipulation can be obtained if the electron is transported adiabatically on a closed path under spin-orbit interaction [7,8].In order to preserve spin information during transport, all other electrons of the heterostructure potentially present along the electron path have to be removed. Therefore all dots have to be emptied and one needs to control them in the so called "few-electron regime". 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. Moreover, the tunability of the four-dot system allows a single electron to be transported along a closed path isolated from the other electrons of the structure. The quantum dot system is fabricated using a GaAs/AlGaAs heterostructure grown by molecular beam epitaxy, with a two-dimensional electron gas (2DEG) 100nm below the surface (density 2 × 10 11 cm −2 and mobility 1 × 10 6 V −1 s −1 ). By applying negative voltages to the meta...

Quantum simulation of a Fermi–Hubbard model using a semiconductor quantum dot array

“…Advances in device size, connectivity and homogeneity are underway as well in the pursuit of scalable quantum computing, the results of which can be directly leveraged. Examples include scalable gate layouts for 1D arrays [37,38] as well as square [39] and triangular [40] geometries, industrial-grade fabrication processes [41] and magnetically quiet 28 Si substrates [42], that open up further possibilities for quantum simulation experiments with quantum dots.…”

Computer-automated tuning of semiconductor double quantum dots into the single-electron regime

“…Future experiments will also address the automated tuning of more than two dots and the tuning of the tunnel couplings in between dots and their reservoirs, which are key parameters for operating dots as qubit devices. Finally, we expect that the same algorithm can be applied with minor modifications to a wide variety of gatedefined quantum dot devices, whether operating in depletion mode 1,4,5,8,11,13,15 or accumulation mode, 9,10 and whether they are based on 2D or 1D 6,7,17 electron systems. In particular, the main steps (identify pinch-off voltages, use those to create single dots, and use those as the starting point for double dots) apply in spirit across all such realizations.…”

“…[4][5][6][7][8][9][10] Enabled by advances in device technology, the number of quantum dots that can be accessed is quickly increasing from very few to many. 11,12 Up to date, all these quantum dots have been tuned by "hand." This is a slow process whereby gate voltages are tweaked carefully, first to reach a regime with one electron in each of the dots and then to adjust the strength of all the tunnel barriers.…”

Minimal Self-Contained Quantum Refrigeration Machine Based on Four Quantum Dots

“…Quadridots in GaAs/AlGaAs heterostructures have been implemented for Cellular-Automata computation [23] and for single-electron manipulation [24]. Strongly capacitively-coupled QDs with interdot capacitance energy (U ⊥ and U ) up to 1/3 of the intra-dot charging energy (taken to be infinite in our model) can be fabricated with current lithographic techniques [25].…”