Sergei Studenikin

National Research Council Canada
Talk title
Hyperfine Effects in GaAs Single Hole Qubits
Abstract Invited

Valence band holes involve over an order of magnitude weaker interaction with nuclei compared to electrons due to the p-type character of the hole wavefunction orbitals.[1] While this is promising for applications involving hybrid quantum systems where qubits defined in direct bandgap materials are required, in this talk experiments will be described which reveal that nuclei-hole spin interactions cannot be neglected in understanding the properties of GaAs hole spin qubits. A double quantum dot circuit tuned to the single hole regime was used in the experiments. We show that under certain conditions the hyperfine coupling remains strong enough to effect nuclear spins flips during the hole EDSR excitation process. Using EDSR in combination with slow magnetic field sweeps we were able to controllably polarize the nuclear field and achieve a maximum polarization of about 25%. The direction of the resultant Overhauser field was fully reversible, achieved by sweeping the applied magnetic field in opposite directions. To gain further insight into the hyperfine phenomena and their consequence on the hole spin parameters additional more complex experiments were performed and will be described in detail. A nuclear spin relaxation time, $T_1$, of ~ 90s was measured using a pump-probe technique. A double-pulse measurement technique which involved alternating microwave bursts and readout pulses revealed B-field dependent oscillations of the Overhauser field vs the delay time between the pulses. The period of these oscillations was found to coincide with the Larmor precession frequency of the 75As nuclear isotopes. Previously we introduced the concept of charge latching for both enhancing the signal to noise during spin readout and for enabling measurements of fast relaxation processes. [2,3]  These have now become commonly used in the field. In the present experiments we employed a variation of this approach to probe coherence times, $T_2^*$ and $T_2$.  The results obtained from Rabi, Ramsey, Hahn-echo, and CPMG pulse sequences will be presented and discussed.

[1] P. Philippopoulos, S. Checi, and Coish, Phys. Rev. B 101, 115302 (2020).
[2] S. Studenikin et al., Appl. Phys. Lett. 101, 233101 (2012).
[3]  A. Bogan et al., Comm. Phys. 2, 17 (2019).