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arXiv:1809.07380 · Applied Physics Letters

Spin readout via spin-to-charge conversion in bulk diamond nitrogen-vacancy ensembles

Harishankar Jayakumar, Siddharth Dhomkar, Jacob Henshaw, Carlos A. Meriles

Published Sep 17, 2018• 26 citations
arXivHTMLPDF

Abstract

We demonstrate the optical readout of ensembles of nitrogen-vacancy (NV) center spins in a bulk diamond sample via spin-to-charge conversion. A high power 594 nm laser is utilized to selectively ionize these paramagnetic defects in the mS=0 spin state with a contrast of up to 12%. In comparison to the conventional 520 nm spin readout, the spin-to-charge-conversion-based readout provides a higher signal-to-noise ratio, with tenfold sensing measurement speedup for millisecond long pulse sequences. This level of performance was achieved for an NV− ionization of only 25%, limited by the ionization and readout laser powers. These observations pave the way to a range of high-sensitivity metrology applications where the use of NV− ensembles in bulk diamond has proven useful, including sensing and imaging of target materials overlaid on the diamond surface.

DOI
10.1063/1.5040261

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We demonstrate the optical readout of ensembles of nitrogen-vacancy (NV) center spins in a bulk diamond sample via spin-to-charge conversion. A high power 594 nm laser is utilized to selectively ionize these paramagnetic defects in the mS=0 spin state with a contrast of up to 12%. In comparison to the conventional 520 nm spin readout, the spin-to-charge-conversion-based readout provides a higher signal-to-noise ratio, with tenfold sensing measurement speedup for millisecond long pulse sequences. This level of performance was achieved for an NV− ionization of only 25%, limited by the ionization and readout laser powers. These observations pave the way to a range of high-sensitivity metrology applications where the use of NV− ensembles in bulk diamond has proven useful, including sensing and imaging of target materials overlaid on the diamond surface.
Nanodiamonds containing nitrogen-vacancy (NV) centers offer a versatile platform for sensing applications spanning from nanomagnetism to in vivo monitoring of cellular processes. In many cases, however, weak optical signals and poor contrast demand long acquisition times that prevent the measurement of environmental dynamics. Here, we demonstrate the ability to perform fast, high-contrast optical measurements of charge distributions in ensembles of NV centers in nanodiamonds and use the technique to improve the spin-readout signal-to-noise ratio through spin-to-charge conversion. A study of 38 nanodiamonds with sizes ranging between 20 and 70 nm, each hosting a small ensemble of NV centers, uncovers complex, multiple time scale dynamics due to radiative and nonradiative ionization and recombination processes. Nonetheless, the NV-containing nanodiamonds universally exhibit charge-dependent photoluminescence contrasts and the potential for enhanced spin readout using spin-to-charge conversion. We use the technique to speed up a T 1 relaxometry measurement by a factor of 5.
We propose and experimentally demonstrate a method to strongly increase the sensitivity of spin measurements on nitrogen-vacancy (NV) centers in diamond, which can be readily implemented in existing quantum sensing experiments. While charge state transitions of this defect are generally considered a parasitic effect to be avoided, we show here that these can be used to significantly increase the NV center's spin contrast, a key quantity for high sensitivity magnetometry and high fidelity state readout. The protocol consists of a two-step procedure, in which the charge state of the defect is first purified by a strong laser pulse, followed by weak illumination to obtain high spin polarization. We observe a relative improvement of the readout contrast by 17 %, and infer a reduction of the initialization error of more than 50 %. The contrast enhancement is accompanied by a beneficial increase of the readout signal. For long sequence durations, typically encountered in high-resolution magnetometry, a measurement speedup by a factor of >1.5 is extracted, and we find that the technique is beneficial for sequences of any duration. Additionally, our findings give detailed insight into the charge and spin polarization dynamics of the NV center, and provide actionable insights for direct optical, spin-to-charge, and electrical readout of solid-state spin centres.
The nitrogen-vacancy (NV) center in diamond is a heavily studied defect due to its potential applications to quantum metrology and computation, particularly in ambient conditions. The key mechanism to using the NV in any application lies in the ability to read out the spin state of the defect which is typically done optically. The optical contrast is then the key metric for electron spin readout fidelity and one of the key limiting factors in the NV's overall performance. We present a mechanism for high contrast readout using the spin-to-charge conversion mechanism in conjunction with an electrode to improve the spin contrast by altering the NV energy levels relative to the diamond conduction band. Theoretical modeling predicts an optical spin contrast at 42% which would be the highest optical contrast for the NV at room temperature and the technique opens up a range of alternative research pathways for the NV which are discussed.
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.
We utilize nonlinear absorption to design all-optical protocols that improve both charge-state initialization and spin readout for the nitrogen-vacancy (NV) center in diamond. Nonmonotonic variations in the equilibrium charge state as a function of visible and near-infrared optical power are attributed to competing multiphoton absorption processes. In certain regimes, multicolor illumination enhances the steady-state population of the NV's negative charge state above 90%. At higher NIR intensities, selective ionization of the singlet manifold facilitates a protocol for spin-to-charge conversion that dramatically enhances the spin readout fidelity. We demonstrate a sixfold increase in the signal-to-noise ratio for single-shot spin measurements and demonstrate a pathway towards single-shot electron spin readout at room temperature.
Efficient readout of individual electronic spins associated with atomlike impurities in the solid state is essential for applications in quantum information processing and quantum metrology. We demonstrate a new method for efficient spin readout of nitrogen-vacancy (NV) centers in diamond. The method is based on conversion of the electronic spin state of the NV to a charge-state distribution, followed by single-shot readout of the charge state. Conversion is achieved through a spin-dependent photoionization process in diamond at room temperature. Using NVs in nanofabricated diamond beams, we demonstrate that the resulting spin readout noise is within a factor of 3 of the spin projection noise level. Applications of this technique for nanoscale magnetic sensing are discussed.