The spin of a single hole confined in a planar gated double quantum dot system is manipulated at subharmonic frequencies of the electric dipole spin resonance. This is achieved by taking advantage of the intrinsic strong spin–orbit coupling that exists in the hole system. In our experiments, a single-hole spin is initially placed in one of the quantum dots, while the other dot is kept empty. The hole spin rotations are stimulated due to multiple anti-crossing events with empty spin levels of the other dot during the Landau–Zener–Stückelberg–Majorana interference. Using this technique, we are able to excite and detect spin-flip transitions occurring at high subharmonic frequencies, up to the 12th order.

Germanium (Ge) and silicon (Si), group IV semiconductors, as innovative epitaxial structures, continue to offer improved properties and enhanced parameters for applications in classical and quantum electronics as well as spintronics. The mobility of free carriers is one such parameter that defines the ultimate performance of electronic devices. The dependence of two-dimensional hole gas (2DHG) mobility on 2DHG density in an undoped gate controlled compressively strained Ge quantum well (QW) grown on Si (cs-GoS), with QW thicknesses of 15 and 30 nm, is studied and compared at T = 0.3 K. Experimental results show that 2DHG mobility is higher in the thinner QW. 2DHG mobilities of 3.1 × 106 and 1.55 × 106 cm2 V−1 s−1 are measured in 15 and 30 nm QWs, respectively, with the same carrier density of 0.9 × 1011 cm−2. The results are explained by the existing theory of carriers' scattering on background ionized impurities.

In this paper, we explore alternative approaches to integrate acoustic wave functionalities into non-piezoelectric group IV materials, notably, germanium within germanium-on-silicon (GoS) heterostructures. This material system is promising as a spin qubit platform for scalable quantum computing architectures. We investigate the potential of surface acoustic waves (SAWs) inducing strain as an interaction mechanism that can be used for the manipulation of spin quantum states in lateral gated quantum dot (QD) devices. Using the Bir–Pikus formalism and k · p theory, we describe the theoretical basis for strain-induced modulation of the valence band in the GoS heterostructures. Our simulations demonstrate that the Rayleigh-type SAWs operating at GHz frequencies can create strain profiles that effectively modulate energy levels in quantum dots. Furthermore, replacing the piezoelectric material (AlN in this work) with a non-piezoelectric counterpart (Al2O3) preserves high-quality acoustic wave propagation while enabling purely mechanical coupling mechanisms, thus enhancing qubit coherence by reducing charge noise, which in piezoelectric materials stems from direct coupling between charge fluctuations and phonons. Proxy simulations with a double-plunger-gate system and floating potentials confirm the sensitivity of QD charge configuration energies to induced strain. These findings support SAW-driven detuning and align with recent predictions on strain-mediated spin–orbit coupling in hole spin qubits. This study highlights the promise of SAW-based strain engineering for scalable quantum control in CMOS-compatible platforms, paving the way for future experimental validation and integration with phononic crystals to advance mechanically enabled quantum architectures.

The concurrent achievement of the record-low resistance charge transport and compatibility with spin qubit technology in solid-state materials is a critical milestone for advancing high-speed, energy-efficient classical and quantum electronics technologies. Here, we demonstrate that holes, the positively charged counterparts of electrons, can propagate with exceptional ease in a nanometres-thin compressively strained germanium layer epitaxially grown on a silicon substrate. Through precise material engineering, we achieve a record-breaking hole mobility of 7.15 x 106 cm2V-1s-1 at a density of 1.7 x 1011 cm-2, establishing a new benchmark for hole transport in group-IV semiconductor materials, importantly, epitaxially grown on a silicon substrate. Our work outlines a design strategy for realising an ultra-clean, low-dimensional system that confines highly mobile holes within a quantum well, while maintaining excellent electrostatic tunability. Crucially, the observed high hole mobility is achieved in gated Hall-bar devices, demonstrating their practical viability for scalable cryogenic classical and quantum electronics applications. These findings unlock new opportunities for a high-performance semiconductor platform capable of underpinning the next generation of quantum information processing, cloud data centres, AI-driven technologies and energy-efficient electronics.

Spin exchange between confined holes and nuclei has been demonstrated for zero-dimensional quantum dots by optical techniques but has not been observed for gated planar structures. Here, enabled by strong spin-orbit interaction, and under microwave (MW) illumination, we report hyperfine interaction and dynamic polarization of the nuclei with confined heavy-holes in a GaAs/AlGaAs double quantum dot device. Distinct signatures of the resultant hyperfine field on the electron dipole spin resonance (EDSR) signal include: hysteresis on sweeping the magnetic (B-) field up and down with characteristics that are strongly dependent on both MW power and B-field sweep rate; free bidirectional dragging of the EDSR condition; stable locking on resonance on a timescale of hours; slow temporal change as the hyperfine field decays (T1 nuclear decay time ~ 100 s); and oscillations in time commensurate with Larmor precession of the 75As nuclei. We attain pumped nuclear (Overhauser) fields ~ 25 mT (~20% nuclear polarization).

This corrects the article DOI: 10.1103/PhysRevLett.120.207701.

With the emergence of the quantum computing era, the spin physics of engineered semiconductor materials with large and tuneable effective g* -factor, which is a measure of the interaction between the magnetic field and the spin of the particle, has become of great interest because it offers new physics and engineering tools for spin’s manipulation and its addressable control. Here we suggest a semi-empirical method to determine out of plane effective g *-factor in high mobility 2D hole heterostructures. We experimentally study the electric-field tuneablity of effective g* -factor of holes in a strained germanium quantum well heterostructure. As a result of the material’s engineering, the g* -factor can be tuned in a large range from 13 to 24 that corresponds to the tuneable Zeeman spin splitting of heavy holes in the range from smaller, to equal, and to larger than the orbital Landau level quantization gap.

We present an experimental study of the coherence properties of a single heavy-hole spin qubit formed in one quantum dot of a gated GaAs/AlGaAs double quantum dot device. We use a modified spin-readout latching technique in which the second quantum dot serves both as an auxiliary element for a fast spin-dependent readout within a 200 ns time window and as a register for storing the spin-state information. To manipulate the single-spin qubit, we apply sequences of microwave bursts of various amplitudes and durations to make Rabi, Ramsey, Hahn-echo, and CPMG measurements. As a result of the qubit manipulation protocols combined with the latching spin readout, we determine and discuss the achieved qubit coherence times: T1, TRabi, T2*, and T2CPMG vs. microwave excitation amplitude, detuning, and additional relevant parameters.

We report on non-linear transport phenomena at high filling factor and DC current-induced electronic hydrodynamics in an ultra-high mobility (mu=20x10^6 cm^2/Vs) two-dimensional electron gas in a narrow (15 micron wide) GaAs/AlGaAs Hall bar for DC current densities reaching 0.67 A/m. The various phenomena and the boundaries between the phenomena are captured together in a two-dimensional differential resistivity map as a function of magnetic field (up to 250 mT) and DC current. This map, which resembles a phase diagram, demarcate distinct regions dominated by Shubnikov-de Haas (SdH) oscillations (and phase inversion of these oscillations) around zero DC current; negative magnetoresistance and a double-peak feature (both ballistic in origin) around zero field; and Hall field-induced resistance oscillations (HIROs) radiating out from the origin. From a detailed analysis of the data near zero field, we show that increasing the DC current suppresses the electron-electron scattering length that drives a growing hydrodynamic contribution to both the differential longitudinal and transverse (Hall) resistivities. Our approach to induce hydrodynamics with DC current differs from the more usual approach of changing the temperature. We also find a significant (factor of two to four) difference between the quantum lifetime extracted from SdH oscillations, and the quantum lifetime extracted from HIROs. In addition to observing HIRO peaks up to the seventh order, we observe an unexpected HIRO-like feature close to mid-way between the first-order and the second-order HIRO maxima at high DC current.

The performance of a semiconductor quantum-electronic device ultimately depends on the quality of the semiconductor materials it is made of and on how well the device is isolated from electrostatic fluctuations caused by unavoidable surface charges and other sources of electric noise. Current technology to fabricate quantum semiconductor devices relies on surface gates which impose strong limitations on the maximum distance from the surface where the confining electrostatic potentials can be engineered. Surface gates also introduce strain fields which cause imperfections in the semiconductor crystal structure. Another way to create confining electrostatic potentials inside semiconductors is by means of light and photosensitive dopants. Light can be structured in the form of perfectly parallel sheets of high and low intensity which can penetrate deep into a semiconductor and, importantly, light does not deteriorate the quality of the semiconductor crystal. In this work, we employ these important properties of structured light to form metastable states of photo-sensitive impurities inside a GaAs/AlGaAs quantum well structure in order to create persistent periodic electrostatic potentials at large predetermined distances from the sample surface. The amplitude of the light-induced potential is controlled by gradually increasing the light fluence at the sample surface and simultaneously measuring the amplitude of Weiss commensurability oscillations in the magnetoresistivity.

Subharmonics of electric dipole spin resonance (EDSR) mediated by Landau-Zener-Stuckelberg-Majorana tunneling transitions are studied numerically and analytically in a Zeeman-split four-level system with strong spin-orbit coupling that can be realized, for example, in a GaAs-based double quantum dot in a single-hole regime. The spin qubit is formed in one of the dots and the second dot is used as an auxiliary element to enhance functionality of the spin qubit. In particular, it is found that the spin rotation rate can be essentially enhanced due to the tunnel coupling with the auxiliary dot on both the main EDSR frequency and at its high subharmonics allowing the coherent spin it rotations on a 10-ns timescale. Spin manipulation on high subharmonics is promising for new time-efficient schemes of the spin control and readout in qubit devices operating at high magnetic fields where the main harmonic is inaccessible due to hardware limitations.

We study experimentally and theoretically the in-plane magnetic field dependence of the coupling between dots forming a vertically stacked double dot molecule. The InAsP molecule is grown epitaxially in an InP nanowire and interrogated optically at millikelvin temperatures. The strength of interdot tunneling, leading to the formation of the bonding-antibonding pair of molecular orbitals, is investigated by adjusting the sample geometry. For specific geometries, we show that the interdot coupling can be controlled in-situ using a magnetic field-mediated redistribution of interdot coupling strengths. This is an important milestone in the development of qubits required in future quantum information technologies.

Single-spin state evolution induced by the Landau-Zener-Stuckelberg-Majorana (LZSM) interference in a Zeeman-spit four-level system in a periodically driven double quantum dot is studied theoretically by the Floquet stroboscopic method. An interplay between spin-conserving and spin-flip tunneling processes with the electric dipole spin resonance (EDSR) that is induced in an individual dot and enhanced by the LZSM multiple level crossings with the neighboring quantum dot is investigated as a function of the microwave (MW) frequency, driving amplitude, interdot detuning, and magnetic field. A number of special points in the parameter space are identified, out of which all three features are merged. Under this triple-crossing resonance condition, the interdot tunneling is combined with a fast spin evolution in each dot at the EDSR frequency. Harmonics of the EDSR are revealed in the spin-dependent tunneling maps versus variable magnetic field and MW frequency. The results are applicable for both electron and hole systems with strong spin-orbit interaction and may be useful for developing new time-efficient schemes of the spin control and readout in qubit devices.

Illumination is performed at low temperature on dopant-free two-dimensional electron gases (2DEGs) of varying depths, under unbiased (gates grounded) and biased (gates at a positive or negative voltage) conditions. Unbiased illuminations in 2DEGs located more than 70 nm away from the surface result in a gain in mobility at a given electron density, primarily driven by the reduction of background impurities. In 2DEGs closer to the surface, unbiased illuminations result in a mobility loss, driven by an increase in surface charge density. Biased illuminations performed with positive applied gate voltages result in a mobility gain, whereas those performed with negative applied voltages result in a mobility loss. The magnitude of the mobility gain (loss) weakens with 2DEG depth, and is likely driven by a reduction (increase) in surface charge density. Remarkably, this mobility gain/loss is fully reversible by performing another biased illumination with the appropriate gate voltage, provided both $n$-type and $p$-type Ohmic contacts are present. Experimental results are modeled with Boltzmann transport theory, and possible mechanisms are discussed.

We propose a non-destructive, all-optical technique to imprint embedded lateral superlattices near semiconductor heterostructures by illuminating the samples with a stable interference pattern generated by a phase diffraction grating. We demonstrate the technique on an ultrahigh mobility GaAs/AlGaAs sample with a Si δ-doping by inducing a persistent charge redistribution at cryogenic temperatures in the doping layer containing DX-centers. Weiss commensurability oscillations in the magnetoresistance of the light-induced superlattice are observed and analyzed to obtain its characteristics.

Difference in g factors in multidot structures can form the basis of dot-selective spin manipulation under global microwave irradiation. Employing electric dipole spin resonance facilitated by strong spin-orbit interaction (SOI), we observe differences in the extracted values of the single-hole effective g factors of the constituent quantum dots of a GaAs/AlGaAs double quantum dot device at the level of similar to 5%-10%. We examine the continuous change in the hole g factor with electrical detuning over a wide range of interdot tunnel couplings and for different out-of-plane magnetic fields. The observed tendency of the quantum dot effective g factors to steadily increase on decreasing the interdot coupling or on increasing the magnetic field is attributed to the impact on the SOI of changing the dot confinement potential and heavy-hole light-hole mixing.

We analyze experimentally and theoretically the transport spectra of a gated lateral GaAs double quantum dot containing two holes. The strong spin-orbit interaction present in the hole subband lifts the Pauli spin blockade and allows to map out the complete spectra of the two-hole system. By performing measurements in both source-drain voltage directions, at different detunings and magnetic fields, we carry out quantitative fitting to a Hubbard two-site model accounting for the tunnel coupling to the leads and the spin-flip relaxation process. We extract the singlet-triplet gap and the magnetic field corresponding to the singlet-triplet transition in the double-hole ground state. Additionally, at the singlet-triplet transition we find a resonant enhancement (in the blockaded direction) and suppression of current (in the conduction direction). The current enhancement stems from the multiple resonance of two-hole levels, opening several conduction channels at once. The current suppression arises from the quantum interference of spin-conserving and spin-flipping tunneling processes.

There is rapidly expanding interest in exploiting the spin of valence-band holes rather than conduction-band electrons for spin qubit semiconductor circuits composed of coupled quantum dots. The hole platform offers stronger spin–orbit interaction (SOI), large difference between in-dot-plane and out-of-dot-plane g -factors, i.e. g -factor anisotropy, and a significantly reduced hyperfine coupling to nuclei in the host material. These attributes collectively can deliver fast all-electric coherent spin manipulation, efficient spin-flip inter-dot tunneling channels, a voltage tunable effective g -factor, a g -factor adjustable to nearly zero in an appropriately oriented external magnetic field, and long spin relaxation and coherence times. Here, we review our recent work on the physics of heavy holes confined in a planar GaAs/AlGaAs double quantum dot system with strong SOI. For a single-hole , we have performed resonant tunneling magneto-spectroscopy to extract spin-flip and spin-conserving tunneling strengths, implemented spin-flip Landau–Zener–Stückelberg–Majorana (LZSM) interferometry, determined the spin relaxation time T 1 as a function of magnetic field using a fast single-shot latched charge technique, electrically tuned the effective g -factor revealed by electric dipole spin resonance, and found signatures of the hyperfine interaction and dynamic nuclear polarization with holes. For two-holes , we have measured the energy spectrum in the presence of strong SOI (and so not limited by Pauli spin blockade), quantified the heavy-hole (HH) g -factor anisotropy on tilting the magnetic field, described a scheme to employ HHs whose g -factor is tunable to nearly zero for an in-plane magnetic field for a coherent photon-to-spin interface, and observed a well-defined LZSM interference pattern at small magnetic fields on pulsing through the singlet-triplet anti-crossing.