Driven coherent oscillations of a single electron spin in a quantum dot

The ability to control the quantum state of a single electron spin in a quantum dot is at the heart of recent developments towards a scalable spin-based quantum computer. In combination with the recently demonstrated controlled exchange gate between two neighbouring spins, driven coherent single spin rotations would permit universal quantum operations. Here, we report the experimental realization of single electron spin rotations in a double quantum dot. First, we apply a continuous-wave oscillating magnetic field, generated on-chip, and observe electron spin resonance in spin-dependent transport measurements through the two dots. Next, we coherently control the quantum state of the electron spin by applying short bursts of the oscillating magnetic field and observe about eight oscillations of the spin state (so-called Rabi oscillations) during a microsecond burst. These results demonstrate the feasibility of operating single-electron spins in a quantum dot as quantum bits. One of the most promising approaches to realizing a practical quantum bit is to use spin states of single electrons in semiconductor quantum dots. A detailed proposal for such spin qubits was published about ten years ago; since then, all the necessary ingredients to realize it, such as long-lived spin states and the initialization of electron spins, have been reported one by one. Now the last, most difficult step has been accomplished, that of driving coherent spin oscillations for individual electrons, which is necessary to carry out quantum operations. This is achieved by applying oscillating magnetic fields that are resonant with the precession frequencies of the electron spins, generated on-chip near a double quantum dot system. All is now ready to design universal quantum logic gates.