Extending the Quantum Coherence of a Near-Surface Qubit by Coherently Driving the Paramagnetic Surface Environment

Abstract

Surfaces enable useful functionalities for quantum systems, e.g. as interfaces to sensing targets, but often result in surface-induced decoherence where unpaired electron spins are common culprits. Here we show that the coherence time of a near-surface qubit is increased by coherent radio-frequency driving of surface electron spins, where we use a diamond nitrogen-vacancy (NV) center as a model qubit. This technique is complementary to other methods of suppressing decoherence, and importantly, requires no additional materials processing or control of the qubit. Further, by combining driving with the increased magnetic susceptibility of the double-quantum basis we realize an overall fivefold sensitivity enhancement in NV magnetometry. Informed by our results, we discuss a path toward relaxation-limited coherence times for near-surface NV centers. The surface spin driving technique presented here is broadly applicable to a wide variety of qubit platforms afflicted by surface-induced decoherence. arXiv:1905.06405v1 [quant-ph]

Stability of superconducting resonators: Motional narrowing and the role of Landau-Zener driving of two-level defects

“…Such behavior is indicative of motional narrowing (motional averaging) (27), where a multilevel system transitions into a single-level system that also exhibits increased spectral stability. Motional narrowing is a common phenomenon that has been found in a wide variety of systems: nuclear magnetic resonance spectra (27,34), electron spin resonance spectra (28), gamma emissions (29), and two-level NV center defects (35,36). Li et al (37) experimentally simulated motional narrowing of the spectroscopic transition in superconducting qubits and suggested that driving the TLS would reduce qubit dephasing; otherwise, despite the similarity between an NV center and a parasitic TLS, motional narrowing has not been considered in the framework of dielectric loss, charge noise, or other TLS phenomena affecting superconducting circuits.…”

Temperature dependence of the longitudinal spin relaxation time T1 of single nitrogen-vacancy centers in nanodiamonds

“…Shedding light on the spin relaxation processes at stake for NV centers in nanodiamonds, our work opens a way to a better understanding of the origin of diamond surface impurities. Ultimately, the influence of these impurities on the relaxation could be reduced using surface cleaning techniques [31] or could be compensated using quantum control protocols [32].…”

Perspectives on deterministic control of quantum point defects by scanned probes

“…T 2 > 1 ms) are only observed for defects >20 nm below the surface [44][45][46][47]. This is attributed to electromagnetic fluctuations due to surface DB or adsorbed species associated with the chemical treatments needed to prepare the samples [45,46,48]. Proximity to the surface is desirable to enhance the coupling to nano-photonics and nanomechanical structures, to increase the sensitivity and spatial resolution in QPD-based sensing, and would also make these defects accessible to scanned probes.…”

“…Proximity to the surface is desirable to enhance the coupling to nano-photonics and nanomechanical structures, to increase the sensitivity and spatial resolution in QPD-based sensing, and would also make these defects accessible to scanned probes. Great efforts were made to mitigate the surface effects including material treatments for better surface engineering [49] and applications of various quantum control algorithms such as dynamical decoupling and double resonance measurements [45,46,48]. These methods have resulted in improved coherence times of T 2 ~ 0.1 ms for NVs only several nanometers below the surface [45,46,48], but this still falls short of the records for bulk NV centers.…”