Vanishing Zeeman energy in a two-dimensional hole gas

Abstract

A clear signature of Zeeman split states crossing is observed in a Landau fan diagram of strained germanium two-dimensional hole gas. The underlying mechanisms are discussed based on a perturbative model yielding a closed formula for the critical magnetic fields. These fields depend strongly on the energy difference between the topmost and neighboring valence bands and are sensitive to the quantum well thickness, strain, and spin-orbit interaction. The latter is a necessary feature for the crossing to occur. This framework enables a straightforward quantification of the hole-state parameters from simple measurements, thus paving the way for its use in design and modeling of hole-based quantum devices.

Nanoscale Mapping of the 3D Strain Tensor in a Germanium Quantum Well Hosting a Functional Spin Qubit Device

“…To assess the spatial variation of these quantities, we have diagonalized the bulk 6 × 6 Luttinger–Khon Hamiltonian, , at the Γ point of Brillouin’s zone, including the strain contribution described by the six independent elements of ε through the Bir–Pikus perturbative approach . To account for the possible impact of the strain on the qubit operation, we have plotted in Figure the behavior of the HH–LH energy difference, since this energy separation determines key properties of the two-dimensional hole gas such as the effective mass, g -factor, and spin–orbit coupling strength and, in turn, may influence spin qubit properties such as Rabi frequencies and coherence times . In detail, in Figure e,f we show the HH–LH band edge gap calculated at RT using the experimental and simulated strain profiles obtained for the cuts shown in Figure a and Figure c, respectively (the individual energy profiles for the HH and LH band edges are shown in Figure S13).…”

Nuclear Spin‐Depleted, Isotopically Enriched 70Ge/28Si70Ge Quantum Wells

“…[9] The latter, for instance, aims at capitalizing on the advantageous quantum environment of holes in Ge, their inherently large and tunable spinorbit interaction (SOI), and their reduced hyperfine coupling with nuclear spins to implement increasingly robust and reliable spin qubits. [10][11][12][13][14][15][16][17][18][19] Indeed, these quantum devices are now considered forefront candidates for scalable quantum processors. [9] This recent surge in developing Ge qubits makes one think that Ge may also be a key material in shaping the anticipated second quantum revolution.…”

Lightly-strained germanium quantum wells with hole mobility exceeding one million

“…The development of undoped Ge/SiGe heterostructures with low-disorder [1,2] has positioned planar Ge as a front-runner platform for hosting high-performance spin-qubit quantum processors based on quantum dots [3][4][5][6][7]. Key properties of holes in planar Ge that are appealing for quantum information processing [8] include: a light hole effective mass (∼ 0.05m e at zero density) [9,10] that gives rise to large orbital splittings in quantum dots [3], sizable and tunable spin-orbit coupling (SOC) for all-electrical fast qubit driving [4], absence of valley degeneracy [10,11], and compatibility with advanced semiconductor manufacturing [12]. Furthermore, the capability to host superconducting pairing correlations [13][14][15] is promising for the co-integration of spin-qubits with superconductors in hybrid architectures [8].…”

“…Alternatively, higher strained Ge (ε // = −1.18 %) on Si 0.25 Ge 0.75 SRBs enabled singlet-triplet spin qubits [6]. Lightly-strained Ge/SiGe heterostructures are unexplored and could offer potentially larger SOC because of the reduced energy splitting between heavy-holes (HH) and light holes (LH) [16], which is ≈ 17 meV for Ge/Si 0.1 Ge 0.9 compared to ≈ 51 meV for Ge/Si 0.2 Ge 0.8 , respectively [10,11]. As such, lightly-strained Ge is interesting for exploring faster spin-qubit driving and for topological devices.…”