Watching Qubits At Work

Light can be used to study the evolution of the quantum state in defects.


As previously discussed, part of the appeal of qubits based on nitrogen-vacancy (N-V) defect centers in diamond is the ability to manipulate them with light. Light pulses can be used both to initialize the qubit array and to measure the results of quantum computations.

As recent work at The University of Chicago shows, light can also be used to study the evolution of the quantum state in these defects. The Chicago researchers used a pair of picosecond pulses of laser light to illuminate N-V centers. The first pulse excites the center, while the second measures its quantum state. By increasing the time between pulses from femtoseconds to nanoseconds, the researchers obtained a series of snapshots showing how the quantum state evolves over time.

The technique, which the authors call “time-domain quantum tomography,” is potentially applicable to many other systems: for it to work, it is only necessary that light can be used to excite an electron from the ground state.