Complete coherent control of a single electron spin in a quantum dot using ultrafast optical pulses

摘要

We demonstrate a complete set of fast, all-optical single-qubit operations on a single electron spin confined in a semiconductor quantum dot (QD). Optical initialization and measurement of the single spin are accomplished by optical pumping in a 3.4 ns timescale with 92±7% fidelity. The spin is coherently manipulated by a single red-detuned broadband laser pulse with 4 picosecond duration. We achieve over six complete Rabi oscillations between the two spin states by varying the rotation pulse's intensity. The fidelity of π/2 and π rotations both exceed 90%. Next we use two sequential rotation pulses, separated by a variable time delay, to demonstrate a complete set of Ramsey fringes. This two-pulse sequence is sufficient to achieve an arbitrary rotation of the spin and thus serves as a universal single-qubit gate.