All posts by cmeriles_1ry5wvws

01-22: Our proposal for mw-free DNP goes live in PRL

Dynamic Nuclear Polarization (DNP) presently stands as the preferred strategy to enhance the sensitivity of nuclear magnetic resonance measurements, but its application relies on the use of high-frequency microwave to manipulate electron spins, an increasingly demanding task as the applied magnetic field grows. Here we investigate the dynamics of a system hosting a polarizing agent formed by two distinct paramagnetic centers near a level anti-crossing. We theoretically show that nuclear spins polarize efficiently under a cyclic protocol that combines alternating thermal jumps and radio-frequency pulses connecting hybrid states with opposite nuclear and electronic spin alignment. Central to this process is the difference between the spin-lattice relaxation times of either electron spin species, transiently driving the electronic spin bath out of equilibrium after each thermal jump. Without the need for microwave excitation, this route to enhanced nuclear polarization may prove convenient, particularly if the polarizing agent is designed to feature electronic level anti-crossings at high magnetic fields.

11-21: Artur’s work on charge-to-photon imaging of dark point defects accepted in Science Advances. Congrats, Artur!

The application of color centers in wide-bandgap semiconductors to nanoscale sensing and quantum information processing largely rests on our knowledge of the surrounding crystalline lattice, often obscured by the countless classes of point defects the material can host. Here we monitor the fluorescence from a negatively charged nitrogen-vacancy (NV) center in diamond as we illuminate its vicinity. Cyclic charge state conversion of neighboring point defects sensitive to the excitation beam leads to a position-dependent stream of photo-generated carriers whose capture by the probe NV leads to a fluorescence change. This “charge-to-photon” conversion scheme allows us to image other individual point defects surrounding the probe NV, including non-fluorescent “single-charge emitters” that would otherwise remain unnoticed. Given the ubiquity of color center photo-chromism, this strategy may likely find extensions to material systems other than diamond.

8-21: Artur’s work on charge transfer between individual NVs accepted in Nature Electronics! Way to go, Artur!

In these experiments, a ‘source’ NV undergoes optically-driven cycles of ionization and recombination to produce a stream of photo-generated carriers, one of which we subsequently capture via a ‘target’ NV several micrometers away. Our observations suggest the formation of bound exciton states with large orbital radii, here enabled through the action of unscreened Coulomb potentials. These states manifest in the form of giant carrier capture cross-sections, orders of magnitude greater than anticipated. Besides their fundamental interest, our results open intriguing prospects in the use of free carriers as a quantum bus to mediate effective interactions between paramagnetic defects in a solid-state chip.

11-20: Hari’s paper on charge-based storage of spin state accepted in Phys. Rev. Lett. Congratulations to Hari and his co-authors!

We articulate confocal microscopy and electron spin resonance to implement spin-to-charge conversion in a small ensemble of nitrogen-vacancy (NV) centers in bulk diamond, and demonstrate charge conversion of neighboring defects conditional on the NV spin state. We build on this observation to show time-resolved NV spin manipulation and ancilla-charge-aided NV spin state detection via integrated measurements. Our results hint at intriguing opportunities in the development of novel measurement strategies in fundamental science and quantum spintronics as well as in the search for enhanced forms of color-center-based metrology down to the limit of individual point defects.