Few-hole double quantum dot in an undoped GaAs/AlGaAs heterostructure

Abstract

We demonstrate a hole double quantum dot in an undoped GaAs/AlGaAs heterostructure. The interdot coupling can be tuned over a wide range, from formation of a large single dot to two well-isolated quantum dots. Using charge sensing, we show the ability to completely empty the dot of holes and control the charge occupation in the few-hole regime. The device should allow for control of individual hole spins in single and double quantum dots in GaAs.One of the leading candidates for a solid-state quantum bit is the spin of a single electron confined in a semiconductor 1 . The pioneering initial experiments demonstrating coherent control of individual electron spins in quantum dots utilized high-mobility twodimensional (2D) electron systems in GaAs/AlGaAs heterostructures 2,3 . The major source of decoherence in such experiments is coupling between electron spins and nuclear spins in the host GaAs semiconductor 2,4 . It has been proposed that hole spins in GaAs would be better suited for such experiments due to a lesser coupling between hole and nuclear spins 5-8 . The stronger spin-orbit interaction for holes, as compared to electrons, may also provide a means for electrical spin manipulation 9,10 .To date, experiments on single spins in semiconductor quantum dots have primarily focused on electron spins. Confinement of single hole spins in nanowire devices 10,11 and self-assembled quantum dots 6-8 has been demonstrated, but fabrication of quatum dots using conventional 2D heterostructures has potential advantages in terms of flexibility of tuning the confinement potential and for fabrication of mulitple dot devices 12,13 . One of the main reasons for the lack of experiments on hole quantum dots in GaAs is the difficulty of fabricating electrically stable nanostructures (such as quantum dots) in p-doped GaAs/AlGaAs heterostructures 14-16 . However, undoped, enhancement-mode devices provide an alternate route to fabricating p-type nanostructures in GaAs. High-mobility two-dimensional hole systems have already been demonstrated in undoped devices [17][18][19] and recent results have shown that a stable many-hole quantum dot can be formed in an enhancement-mode device in a (311)A oriented heterostructure with a p-doped cap layer 20 .In this article, we report fabrication and measurement of a hole double quantum dot (DQD) in an undoped (100) oriented GaAs/AlGaAs heterostructure. The mean free path in similarly processed bulk 2D devices at T = 4 K, at density of p = 2 × 10 11 cm −2 is ∼1 µm, which is larger than typical nanostructure dimensions, aiding in the formation of low-disorder few-hole nanostructures. The gate design 21 provides a high degree of tunability, allowing for independent control over individual dot occupation and tunnel barriers, as well as the ability to use a nearby quantum point contacts (QPCs) to sense dot charge occupation. We show the ability to control the coupling between dots, tuning the device across the transition from one large dot to two well-isolated quantum dots. Using charge sensing, we...

Spin-orbit interactions in inversion-asymmetric two-dimensional hole systems: A variational analysis

“…The search for semiconductor systems with strong spin-orbit coupling has led naturally to lowdimensional hole systems. [7][8][9] Despite the promising advances of recent years, in particular in the experimental state of the art, [10][11][12][13][14][15][16][17][18][19][20][21][22] functional hole spin-based devices are yet to be realized. In particular, a comprehensive understanding of the interaction between a hole's spin and its solid-state environment is far from complete.…”

Double-layer-gate architecture for few-hole GaAs quantum dots

“…However, due to the large effective mass (m * h /m * e ∼ 3 − 13) [12], hole quantum dots need to have much smaller dimensions compared to electron dots to show similar single particle energy scales since the orbital energies E orb ∼ 1/m * A dot , which is hard to achieve by simply duplicating the design for electron quantum dots. Even though the operation of GaAs single hole transistors has been demonstrated [13,14,15], to date it has not been possible to observe Zeeman splitting of the single particle levels, which is a prerequisite for measurements of the T 1 and T * 2 spin lifetimes, and for coherent spin manipulation.…”

Consequences of Spin-Orbit Coupling at the Single Hole Level: Spin-Flip Tunneling and the Anisotropic g Factor

“…We explore high-bias magneto-transport properties of a ptype AlGaAs/GaAs DQD [10]. Charge detection is used to tune the DQD to the two-hole regime, where certain tunneling transitions requiring spin flips are subject to Pauli spin blockade [11].…”