Dynamical decoupling of a single-electron spin at room temperature

Here we report the increase of the coherence time $T$${}_2$ of a single-electron spin at room temperature by using dynamical decoupling. We show that the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence can prolong the $T$${}_2$ of a single nitrogen-vacancy center in diamond up to 2.44 ms compared to the Hahn echo measurement where $T$${}_2=400\hspace{0.5em}\mu$s. Moreover, by performing spin-locking experiments we demonstrate that with CPMG the maximum possible $T_2$ is reached. On the other hand, we do not observe a strong increase of the coherence time in nanodiamonds, possibly due to the short spin-lattice relaxation time $T_1=100\hspace{0.5em}\mu$s (compared to $T$${}_1$$=5.93$ ms in bulk). An application for detecting low magnetic fields is demonstrated, where we show that the sensitivity using the CPMG method is improved by about a factor of 2 compared to the Hahn echo method.

Figure 1

(a) Schematic view of the NV center in diamond. (b) Energy-level scheme of NV. A green laser excites the NV to ${}^{3}E$, from which it can fall back to ${}^{3}A$ or undergo intersystem crossing to a metastable state ${}^{1}A$. From there it decays to the $m_s=0$ ground state, thus polarizing the electron spin.

Figure 2

Pulse sequences used in the experiments. The curved lines represent the applied ac magnetic field. (a) Optical polarization and readout of the NV electron spin, (b) Hahn echo, (c) CPMG, and (d) spin locking (see text for more details).

Figure 3

Hahn echo decay (inset, $T_2=0.4\pm 0.16$ ms), CPMG (circles, $T_2^{\mathrm{CPMG}}=2.44\pm 0.44$ ms), spin locking (triangles, $T_{1\rho }=2.47\pm 0.27$ ms), and spin-lattice relaxation (squares, $T_1=5.93\pm 0.7$ ms). The solid curves are fits to the data (see text).

Figure 4

The graph represents $\delta B_{\min }$ as a function of the total measurement time per data point for Hahn echo and CPMG based magnetometry. The blue line denotes fits with the shot-noise limit $\delta B_{\min }=\frac{k}{\sqrt{t}}$. The inset shows the oscillations in the fluorescence intensity due to the applied ac magnetic field.