Tramea

Temperature-dependent transport measurements are performed on the same
set of chemical vapor deposition (CVD)-grown WS₂ single- and bilayer devices
before and after atomic layer deposition (ALD) of HfO₂. This isolates the influence
of HfO₂ deposition on low-temperature carrier transport and shows that
carrier mobility is not charge impurity limited as commonly thought, but due
to another important but commonly overlooked factor: interface roughness.
This finding is corroborated by circular dichroic photoluminescence spectroscopy,
X-ray photoemission spectroscopy, cross-sectional scanning transmission
electron microscopy, carrier-transport modeling, and density functional
modeling. Finally, electrostatic gate-defined quantum confinement is demonstrated
using a scalable approach of large-area CVD-grown bilayer WS₂
and ALD-grown HfO₂. The high dielectric constant and low leakage current
enabled by HfO₂ allows an estimated quantum dot size as small as 58 nm.
The ability to lithographically define increasingly smaller devices is especially
important for transition metal dichalcogenides due to their large effective
masses, and should pave the way toward their use in quantum information
processing applications.

C. S. Lau, J. Y. Chee, Z.-E. Ooi, S. W. Tong, M. Bosman, F. Bussolotti,
T. Wang, S. L. Teo, C. P. Y. Wong, J. W. Chai, Z. M. Zhang, K.-W. Ang, and
K. E. J. Goh
Adv. Mater. 2021, 2103907

The non-trivial topology of three-dimensional topological insulators dictates the appearance of gapless Dirac surface states. Intriguingly, when made into a nanowire, quantum confinement leads to a peculiar gapped Dirac sub-band structure. This gap is useful for, e.g., future Majorana qubits based on TIs. Furthermore, these sub-bands can be manipulated by a magnetic flux and are an ideal platform for generating stable Majorana zero modes, playing a key role in topological quantum computing. However, direct evidence for the Dirac sub-bands in TI nanowires has not been reported so far. Here, using devices fabricated from thin bulk-insulating (Bi_1−xSb_x)₂Te₃ nanowires we show that non-equidistant resistance peaks, observed upon gate-tuning the chemical potential across the Dirac point, are the unique signatures of the quantized sub-bands. These TI nanowires open the way to address the topological mesoscopic physics, and eventually the Majorana physics when proximitized by an s-wave superconductor.

F. Münning, O. Breunig, H. F. Legg, S. Roitsch, D. Fan, M. Rößler, A. Rosch, and Y. Ando
Nat Commun 12, 1038 (2021)

A controllable and coherent light-matter interface is an essential element for a scalable quantum information processor. Strong coupling to an on-chip cavity has been accomplished in various electron quantum dot systems, but rarely explored in the hole systems. Here we demonstrate a hybrid architecture comprising a microwave transmission line resonator controllably coupled to a hole charge qubit formed in a Ge/Si core/shell nanowire (NW), which is a natural one-dimensional hole gas with a strong spin–orbit interaction (SOI) and lack of nuclear spin scattering, potentially enabling fast spin manipulation by electric manners and long coherence times. The charge qubit is established in a double quantum dot defined by local electrical gates. Qubit transition energy can be independently tuned by the electrochemical potential difference and the tunnel coupling between the adjacent dots, opening transverse (σx) and longitudinal (σz) degrees of freedom for qubit operation and interaction. As the qubit energy is swept across the photon level, the coupling with resonator is thus switched on and off, as detected by resonator transmission spectroscopy. The observed resonance dynamics is replicated by a complete quantum numerical simulation considering an efficient charge dipole-photon coupling with a strength up to 2π × 55 MHz, yielding an estimation of the spin-resonator coupling rate through SOI to be about 10 MHz. The results inspire the future researches on the coherent hole-photon interaction in Ge/Si nanowires.

R. Wang, R. S. Deacon, J. Sun, J. Yao, C. M. Lieber and K. Ishibashi
Nano Lett. 2019, 19, 2, 1052-1060