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

Future communication and computation technologies that exploit quantum information require robust and well-isolated qubits. Electron spins in III-V semiconductor quantum dots, although promising candidate qubits, see their dynamics limited by undesirable hysteresis and decohering effects of the nuclear spin bath. Replacing electrons with valence-band holes should suppress the hyperfine interaction and consequently eliminate strong nuclear effects. Such suppression was recently observed in optical initialization and coherent population trapping experiments, but complete control over the phase of an arbitrary hole superposition-the essence of a hole-based qubit-has not yet been achieved. Using picosecond optical pulses, we now demonstrate complete coherent control of a single hole qubit and examine both free-induction and spin-echo decay. In moving from electrons to holes, we observe the effects of the reduced hyperfine interactions in the re-emergence 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.