Ultrafast coherent control and suppressed nuclear feedback of a single quantum dot hole qubit

Abstract

Future communication and computation technologies that exploit quantum information require robust and well-isolated qubits. Electron spins in III-V semiconductor quantum dots, while promising candidates, see their dynamics limited by undesirable hysteresis and decohering effects of the nuclear spin bath. Replacing electrons with holes should suppress the hyperfine interaction and consequently eliminate strong nuclear effects. Using picosecond optical pulses, we demonstrate coherent control of a single hole qubit and examine both free-induction and spin-echo decay. In moving from electrons to holes, we observe significantly reduced hyperfine interactions, evidenced by the reemergence of hysteresis-free dynamics, while obtaining similar coherence times, limited by non-nuclear mechanisms. These results demonstrate the potential of optically controlled, quantum dot hole qubits. arXiv:1106.5676v1 [quant-ph]

Polarization-correlated photons from a positively charged quantum dot

“…Without applied magnetic field some experiments suggest the hole spin T h 1 time is 13 ns [8]. Several studies have now estimated the hole dephasing time, T h 2 in magnetic field is approximately 1 µs [3,17].…”

“…Optical measurements have demonstrated spin preparation [1, 2] coherent spin control [3] and electron-spin − photon entanglement [4,5]. There are also proposals for achieving photon entanglement [6] and non-destructive measurement of photons [7] using charged QDs.…”

“…Without applied magnetic field some experiments suggest the hole spin T h 1 time is 13 ns [8]. Several studies have now estimated the hole dephasing time, T h 2 in magnetic field is approximately 1 µs [3,17].We study here the emission from the X + state in a dot deterministically charged with a hole using a diode * Electronic address: anthony.bennett@crl.toshiba.co.uk ( Figure 1a). We show photons from this transition display polarization correlation over a timescale one order of magnitude greater than the radiative lifetime when excited by a linearly polarized laser.…”

Hole spin relaxation in InAs/GaAs quantum dot molecules

“…This is inspite of their promising prospects for the development of quantum information architectures. [10,15,19] Understanding the hole spin dynamics in DQDs is also of relevance for recently proposed exciton spin based qubits, [33] since hole relaxation usually determines the excitonic spin lifetime.…”

“…[3,4] Additionally, the p-type symmetry of the valence band orbitals causes a weak hyperfine interaction with the lattice nuclei, thus giving rise to decoherence times potentially longer than those of electron spins. [5,6,7,8,9,10,11] This has enabled successful hole spin initialization [12] and coherent control [10,13]. Double quantum dots (DQDs) are a natural extension which should facilitate the use of independent optical transitions for spin preparation, manipulation and readout, [14] as well as the scalability towards multiple qubit architectures.…”