Spectroscopy of Spin-Orbit Quantum Bits in Indium Antimonide Nanowires

Abstract

Double quantum dot in the few-electron regime is achieved using local gating in an InSb nanowire. The spectrum of two-electron eigenstates is investigated using electric dipole spin resonance. Singlettriplet level repulsion caused by spin-orbit interaction is observed. The size and the anisotropy of singlet-triplet repulsion are used to determine the magnitude and the orientation of the spin-orbit effective field in an InSb nanowire double dot. The obtained results are confirmed using spin blockade leakage current anisotropy and transport spectroscopy of individual quantum dots.PACS numbers: 73.63. Kv, 85.35.Be The spin-orbit interaction (SOI) describes coupling between the motion of an electron and its spin. In one dimension, where electrons can move only to the left or to the right, the SOI couples this left or right motion to either spin-up or spin-down. An extreme situation occurs in what is called a helical liquid [1] where, in the presence of magnetic field, all spin-up electrons move to the left and all spin-down electrons to the right. As proposed recently [2,3], a helical liquid in proximity to a superconductor can generate Majorana fermions [4]. The search for Majorana fermions in 1D conductors is focused on finding the best material in terms of a strong spin-orbit interaction and large Landé g-factors. The latter is required for a helical liquid to exist at magnetic fields that do not suppress superconductivity. High g-factors of the order 50, strong SOI and the ability to induce superconductivity put forward InSb nanowires [5,6] as a natural platform for the realization of 1D topological states.The SOI can be expressed as an effective magnetic field B SO that depends on the electron momentum. An electron moving through the wire undergoes spin precession around B SO with a π rotation over a distance l SO called the spin-orbit length (see Fig. 1(a)). The length l SO is a direct measure of the SOI strength: a stronger SOI results in a shorter l SO . In this letter, we use spin spectra of single electrons in quantum dots [7] to extract l SO and the direction of B SO . In quantum dots, the SOI hybridizes states with different spin [5,8,9]. For a single electron, the SOI-hybridized spin-up and spin-down states form a spin-orbit qubit [10,11]. For two electrons SOI hybridization induces level repulsion between singlet and triplet states. The resulting level-repulsion gap between the well-defined qubit states can be used to measure the SOI: the gap size is determined by l SO [5,8,9] and the gap anisotropy indicates the direction of B SO [12][13][14]. Double quantum dots in InSb nanowires are defined by local gating (Figs. 1(b),1(c)). A finite voltage is applied across the source and drain electrodes; and the current through the nanowire is measured. Five gates underneath the wire create the confinement potential and control the electron number on the two dots [9,15]. We focus on the (1,1) charge configuration ( Fig. 1(d)), in which both the left and the right dot contain exactly one electron, each of them...

Maximal Rabi frequency of an electrically driven spin in a disordered magnetic field

“…Subharmonic spin resonances have recently been observed [3][4][5][6][7] in electrically driven quantum dots (QDs) [8][9][10][11][12]. In these systems, electrical driving might be favorable over magnetic excitation, as the former allows for selective addressing of spin-based quantum bits in a multi-quantum-dot register.…”

To Screen or Not to Screen, That is the Question!

“…The interest in such new materials relies on the wealth of different phenomena they present (Kondo effect, 6,7 spin-orbit coupling, [8][9][10] Luttinger liquid behavior 11 ) and their interplay when coupled to superconducting reservoirs. Further interest in this field has been prompted by recent theoretical predictions on the existence of Majorana fermions at the edge of a S-X structure, where X is a one-dimensional semiconductor with strong spin-orbit interaction.…”

Anisotropic exchange coupling in a nanowire double quantum dot with strong spin-orbit coupling

“…The semiconductor nanowire materials, e.g., InAs [6,[17][18][19] and InSb nanowire [7,20], provide an ideal platform for realizing such a qubit. Indeed, a large Rabi frequency of ∼100 MHz was reported recently for single-qubit operations [21].…”

“…Recently, a hybrid qubit, the spin-orbit qubit [6,7], was achieved in a nanowire quantum dot with strong spin-orbit coupling (SOC). A distinct advantage of this spin-orbit qubit is its manipulability via an electric field (an effect called electric-dipole spin resonance [6][7][8][9][10][11][12][13][14][15]) because a local electric field can be generated in experiments much more easily than a local magnetic field [16].…”