Nanoscale Detection of a Single Fundamental Charge in Ambient Conditions Using the $\mathrm{NV}{}^{-}$ Center in Diamond

Single charge nanoscale detection in ambient conditions is a current frontier in metrology that has diverse interdisciplinary applications. Here, such single charge detection is demonstrated using two nitrogen-vacancy (NV) centers in diamond. One NV center is employed as a sensitive electrometer to detect the change in electric field created by the displacement of a single electron resulting from the optical switching of the other NV center between its neutral ($\mathrm{NV}{}^0$) and negative ($\mathrm{NV}{}^{-}$) charge states. As a consequence, our measurements also provide direct insight into the charge dynamics inside the material.

Figure 1

(a) Schematic of the NV centers under investigation. On the right, NV $A$ is depicted as the electrometer NV, and on the left NV $B$ is responsible for the electric field. (b) Diamond unit cell containing an NV center. The latter is a $C_{3v}$ point defect (see mirror planes) consisting of a substitutional nitrogen (N)—carbon vacancy (V) pair orientated along the $⟨111⟩$ crystal ($z$) axis. The negative charge state ($\mathrm{NV}{}^{-}$) is formed from the neutral $\mathrm{NV}{}^0$ when the center traps an excess electron. The local Cartesian coordinate axes $x$, $y$ and $z$ (blue, orange, green) are shown. (c) Left: Electron spin levels affected by a transverse magnetic field $B_{\perp }$ (here, $B_y$) of varying strength. Right: Effects on energy levels of hyperfine (HF) coupled electron spin nuclear spin pair due to additionally applied electric and longitudinal magnetic fields (Stark and $B_z$, respectively). See text for discussion.

Figure 2

(a) Ramsey measurement sequence including charge state preparation of NV $B$ (red laser pulse), spin state initialization and readout of NV $A$ ($\text{green}\text{laser}+\text{fluorescence}\text{detection}$), microwave pulses for spin control (blue) and free evolution of the spin superposition state (yellow, accumulated phase $\phi$ during time $\tau$). (b) Example Ramsey spectrum revealing four pairs of resonance lines (orange, measurement data, green, multiple Gauss fit). The four pairs are split due to hyperfine interaction (see text). Inset: The splitting within each pair results from the Stark effect. (c) The relative intensity (center) of the Stark-split lines of NV $A$ (left and right inset) can be influenced by pumping NV $B$ from its negative into its neutral charge state with pumping duration ${\tau }_{\text{pump}}$. Thus demonstrating that the Stark effect originates from different charge states of NV $B$.

Figure 3

(a) Electron spin resonance frequencies as obtained from Ramsey oscillations for different auxiliary magnetic fields ($\delta \vec{B}=\mathrm{\Delta }{B}_x\widehat{x}+B_z\widehat{z}$). (b) Polar plot of the electric field shift of a single hyperfine line as the transverse magnetic field $B_{\perp }$ is rotated. (c) Superresolution microscopy image of NV $A$ and NV $B$. (d) Combination of (b),(c) and the known orientations and positions of the centers.