Room-temperature control and electrical readout of individual nitrogen-vacancy nuclear spins.

Nuclear spins in semiconductors are leading candidates for future quantum technologies, including quantum computation, communication, and sensing. Nuclear spins in diamond are particularly attractive due to their long coherence time. With the nitrogen-vacancy (NV) centre, such nuclear qubits benefit from an auxiliary electronic qubit, which, at cryogenic temperatures, enables probabilistic entanglement mediated optically by photonic links. Here, we demonstrate a concept of a microelectronic quantum device at ambient conditions using diamond as wide bandgap semiconductor. The basic quantum processor unit - a single 14N nuclear spin coupled to the NV electron - is read photoelectrically and thus operates in a manner compatible with nanoscale electronics. The underlying theory provides the key ingredients for photoelectric quantum gate operations and readout of nuclear qubit registers. This demonstration is, therefore, a step towards diamond quantum devices with a readout area limited by inter-electrode distance rather than by the diffraction limit. Such scalability could enable the development of electronic quantum processors based on the dipolar interaction of spin-qubits placed at nanoscopic proximity.

A Label-Free Diamond Microfluidic DNA Sensor Based on Active Nitrogen-Vacancy Center Charge State Control.

We propose a label-free biosensor concept based on the charge state manipulation of nitrogen-vacancy (NV) quantum color centers in diamond, combined with an electrochemical microfluidic flow cell sensor, constructed on boron-doped diamond. This device can be set at a defined electrochemical potential, locking onto the particular chemical reaction, whilst the NV center provides the sensing function. The NV charge state occupation is initially prepared by applying a bias voltage on a gate electrode and then subsequently altered by exposure to detected charged molecules. We demonstrate the functionality of the device by performing label-free optical detection of DNA molecules. In this experiment, a monolayer of strongly cationic charged polymer polyethylenimine is used to shift the charge state of near surface NV centers from negatively charged NV- to neutral NV0 or dark positively charged NV+. Immobilization of negatively charged DNA molecules on the surface of the sensor restores the NV centers charge state back to the negatively charged NV-, which is detected using confocal photoluminescence microscopy. Biochemical reactions in the microfluidic channel are characterized by electrochemical impedance spectroscopy. The use of the developed electrochemical device can also be extended to nuclear magnetic resonance spin sensing.

Photoelectrical imaging and coherent spin-state readout of single nitrogen-vacancy centers in diamond.

Nitrogen-vacancy (NV) centers in diamond have become an important instrument for quantum sensing and quantum information science. However, the readout of NV spin state requires bulky optical setups, limiting fabrication of miniaturized compact devices for practical use. Here we realized photoelectrical detection of magnetic resonance as well as Rabi oscillations on a single-defect level. Furthermore, photoelectrical imaging of individual NV centers at room temperature was demonstrated, surpassing conventional optical readout methods by providing high imaging contrast and signal-to-noise ratio. These results pave the way toward fully integrated quantum diamond devices.