Workshop book - Physikzentrum der RWTH Aachen - RWTH Aachen ...

Talks Tuesday February 5
Spin-orbit-mediated control of electron and hole spins in InSb nanowire
quantum dots
Vlad Pribiag, Kavli Institute of Nanoscience Delft, The Netherlands
The spin-orbit interaction allows fast control of individual spins in quantum dots
using electric fields. Narrow-gap III-V semiconductor nanowires (InAs and InSb)
exhibit strong spin-orbit coupling, which makes them a promising platform for spinbased
qubits [1,2]. In this talk I will focus on InSb nanowires, which are of high
interest both for qubits and for observing Majorana fermions.
Using electric-dipole spin resonance (EDSR) we demonstrate coherent and universal
control over the spin-orbit eigenstates of individual electrons, with Rabi
frequencies in excess of 100 MHz and estimated fidelities of ∼ 81%. The large
Zeeman energy difference between adjacent dots enables selective addressing of each
qubit. Furthermore, we use EDSR in the strong interdot coupling regime to probe
the strength and anisotropy of the spin-orbit coupling. The data in agreement with
Rashba spin-orbit coupling, with α∼ 0.23 eVÅ. Although the Rabi oscillations for
InSb nanowire qubits are considerably faster than for GaAs qubits, the coherence
times are relatively short (Techo ∼ 35 ns) and show no significant dependence on
driving frequency within the accessible range of 8-32 GHz. This is consistent with
dephasing due to a fast spin bath that likely originates from the large nuclear spins
of InSb (5/2 and 7/2 for 121Sb and 123Sb respectively, and 9/2 for In).
A promising approach to enhancing qubit coherence is to use hole spins as qubits
instead of electron spins because hole spins exhibit weaker hyperfine coupling [3].
Taking advantage of the small bandgap of InSb, we can readily gate-tune our
nanowire devices between few-electron and few-hole quantum dots [4]. Comparison
between the two regimes suggests that the holes are primarily of light character and
that the hyperfine interaction is about an order of magnitude weaker for holes than
for electrons. We demonstrate rotation of hole spin states via EDSR and use this
to extract the hole g-factor, which is about an order of magnitude smaller than for
electrons. We compare the anisotropies of the g-factor and spin blockade leakage
current for holes and electrons. The ability to control and read out hole spin states
paves the way for coherent, all-electrical hole-spin qubits.
[1] C. Flindt, A. S. Sørensen, K. Flensberg, Phys. Rev. Lett. 97 240501 (2006).
[2] S. Nadj-Perge, S. M. Frolov, E. P. A. M. Bakkers, and L. P. Kouwenhoven,
Nature 468, 1084 (2010).
[3] D. Brunner, B. D. Gerardot, P. A. Dalgarno, G. Wüst, K. Karrai, N. G. Stoltz,
P. M. Petroff, R. J. Warburton, Science 325, 70 (2009).
[4] V. S. Pribiag, S. Nadj-Perge, S. M. Frolov, J. van den Berg, I. van Weperen,
S. R. Plissard, E. P. A. M. Bakkers, and L. P. Kouwenhoven, Submitted.
38