Room-temperature manipulation and decoherence of a single spin in diamond

We report on room-temperature coherent manipulation of the spin of a single nitrogen-vacancy center in diamond and a study of its coherence as a function of magnetic field. We use magnetic resonance to induce Rabi nutations and apply a Hahn spin echo to remove the effect of low-frequency dephasing. A sharp rise in the decoherence rate is observed at magnetic fields where the nitrogen-vacancy center spin couples resonantly to substitutional nitrogen spins via the magnetic dipolar coupling. Finally, we find evidence that away from these energy resonances spin flips of nitrogen electrons are the main source of decoherence.

Figure 1

(a) Electronic level structure of the N-V center. The excited ${}^{3}E$ state is $1.945\mathrm{eV}$ above the ${}^{3}A$ ground state. The spin sublevels of the electronic ground state are manipulated in this work. (b) Electron spin resonance (ESR) between the $m_S=0$ and $m_S=-1$ spin levels of N-V14 at $B=100\mathrm{G}$.

Figure 2

(Color) Coherent manipulation of the electron spin of a single N-V center. (a) Three-step sequence applied: the first laser pulse (typically $5\mu \mathrm{s}$ long) initializes the spin, then the spin manipulation is carried out in the dark, and finally the spin state is read out by a second laser pulse (typically $2\mu \mathrm{s}$ long) (Ref. 21). The sequence is typically repeated 1000 times to increase the signal. Laser power is $500\mu \mathrm{W}$. (b) Driven coherent oscillations (Rabi nutations) of N-V14 at $B=850\mathrm{G}$. The spin is rotated between the $m_S=0$ and the $m_S=-1$ levels, leading to alternating high and low $I_{PL}$. The Rabi nutation frequency is proportional to the square root of the applied rf power, as expected. Curves are offset for clarity. (c) Hahn spin echo pulse sequence. (d) Hahn spin echo signal of N-V14 at $B=850\mathrm{G}$ as a function of the total delay ${\tau }_1+{\tau }_2$.

Figure 3

(Color) Dependence of the coherence on the applied magnetic field $B$. (a) Decoherence rate $1∕T_2^{\prime }$ of N-V14 as a function of $B$. (b) Energy levels of the N-V center and of N electron spin as a function of $B$ along the N-V symmetry axis. An energy resonance occurs around $B=514\mathrm{G}$. (c) $I_{PL}$ of N-V14 as a function of $B$. The dips reflect the reduced spin polarization of the N-V center due to resonant spin exchange with the N electron spin through magnetic dipolar interaction (Refs. 12, 14). (d) $1∕T_2^{\prime }$ of N-V14 as a function of magnetic field, showing stronger decoherence at the fields where $I_{PL}$ dips. The dashed line depicts the average off-resonance value of $1∕T_2^{\prime }$. The red lines in (c) and (d) are Lorentzian fits. (e) $T_2^{\prime }$ at $B=850\mathrm{G}$ versus normalized amplitude of the dip in $I_{PL}$ for five different N-V centers.