Engineering ultralong spin coherence in two-dimensional hole systems at low temperatures

Abstract

For the realisation of scalable solid-state quantum-bit systems, spins in semiconductor quantum dots are promising candidates. A key requirement for quantum logic operations is a sufficiently long coherence time of the spin system. Recently, hole spins in III-V-based quantum dots were discussed as alternatives to electron spins, since the hole spin, in contrast to the electron spin, is not affected by contact hyperfine interaction with the nuclear spins. Here, we report a breakthrough in the spin coherence times of hole ensembles, confined in so called natural quantum dots, in narrow GaAs/AlGaAs quantum wells at temperatures below 500 mK. Consistently, time-resolved Faraday rotation and resonant spin amplification techniques deliver holespin coherence times, which approach in the low magnetic field limit values above 70 ns. The optical initialisation of the hole spin polarisation, as well as the interconnected electron and hole spin dynamics in our samples are well reproduced using a rate equation model.

Terahertz magneto-optical spectroscopy of a two-dimensional hole gas

“…This makes spin coherence very fragile, which can destroy information before it can be processed [8,9]. In this regard, a 2DHG would have an advantage, as the p-type hole valence band has a reduced hyperfine interaction with the nuclei, leading to longer spin coherence times for holes [10,11]. Furthermore, the Rashba effect (electric-field-induced spin splitting) can be made much stronger in a 2DHG than in a 2DEG [12].…”

“…From the slopes of the subbands at the Fermi level, one can determine the semiclassical cyclotron masses. Assuming non-parabolic subbands, we then obtained an approximate effective mass of 0.28m e from the slope of the highest HH band by averaging over the [11] and [10] directions. However, as was shown in ref.…”

Controlling hole spin dynamics in two-dimensional hole systems at low temperatures

“…The resulting g factor inhomogeneity leads to ensemble dephasing with applied magnetic field. This is observed as a characteristic 1/Bdependence of the SDT in 2D hole systems [8]. With increased carrier density close to the 2DHG regime, increased averaging over all holes occurs, leading to a decreased g factor inhomogeneity.…”

“…The techniques used are time resolved Kerr rotation (TRKR) and resonant spin amplification (RSA) [7]. The optical experiments are performed using a pulsed Ti-Sapphire laser system, details of the experiment are published elsewhere [6,8].…”

Resonant spin amplification of hole spin dynamics in two-dimensional hole systems: experiment and simulation

“…It is mounted in an optical cryostat with a 3 He insert, allowing for sample temperatures below 500 mK and magnetic fields of up to 10 Tesla in the sample plane. Optical experiments are performed using a pulsed Ti-Sapphire laser system, details of the experiment are published elsewhere [10]. No RSA maximum is observed in zero field, and for finite fields, the amplitude of the RSA maxima first increases, then decreases again, leading to a butterfly-like shape of the signal, which stems from the complex initialization process of a resident hole spin polarization using optical orientation [10].…”