Figure 1

This simple energy level scheme describes the observed optical properties of the defect center in diamond as two coupled two-level systems (TLS). In the first TLS, the center can be excited with a red light of wavelength 680 nm, responding with a Stokes shifted fluorescence of rate $k_b^{-1}=5.5\mathrm{ns}$. The second TLS is excited with a green light of wavelength 514 nm and decays nonradiatively with rate $k_d$. Since these nanosecond transitions are not resolved, the first TLS appears as bright whereas the second TLS is dark. Depending on the intensity of the red excitation light, the bright TLS decays with another rate $b$ into the dark TLS, from which it can be pumped back with rate $a$ using the green laser. The transition rates $a$ and $b$ between the two TLSs are several orders of magnitude smaller than $k_b$ and $k_d$ and depend linearly on the intensities of the green (rate $a$) and red (rate $b$) laser, respectively, (data not shown). Hence, it is sufficient to consider the whole system as one effective TLS with a dark and a bright state.Reuse & Permissions

Figure 2

Experimental test of the fluctuation theorem (2). The main frame shows mean $⟨\exp (-R)⟩$ for trajectories of length $t$, for three different parameter values: (1) $a_0^{-1}=26\mathrm{ms}$, $b_0^{-1}=31\mathrm{ms}$, $t_{\mathrm{m}}=50\mathrm{ms}$, $\gamma =0.07$ for 1000 traces; (2) $a_0^{-1}=27\mathrm{ms}$, $b_0^{-1}=31\mathrm{ms}$, $t_{\mathrm{m}}=50\mathrm{ms}$, $\gamma =0.14$ for 1100 traces; (3) $a_0^{-1}=64\mathrm{ms}$, $b_0^{-1}=30\mathrm{ms}$, $t_{\mathrm{m}}=20\mathrm{ms}$, $\gamma =0.23$ for 4000 traces. The inset shows both the modulated intensity of the green laser and the fluorescence signal with the filtered trajectory $n(\tau )$ of an example trace of experiment (2).Reuse & Permissions

Figure 3

Comparison of the numerically calculated probability distribution $P(R)$ with the experimentally obtained normalized histogram at times (a) $\tau =60\mathrm{ms}$ and (b) $\tau =200\mathrm{ms}$. (In both cases: $a_0^{-1}=64\mathrm{ms}$, $b_0^{-1}=30\mathrm{ms}$, $t_{\mathrm{m}}=20\mathrm{ms}$, and $\gamma =0.23$.)Reuse & Permissions

Figure 4

Test of the moment relation (13) for the second ($k=2$) and fourth ($k=4$) moment. The plots show the ratio $⟨R^k{e}^{-R}⟩/⟨R^k⟩$ over trajectory length $t$ for $t_{\mathrm{m}}=20\mathrm{ms}$. At the vertical dashed lines the protocol becomes symmetric; see Eq. (11). (a) Experimental data; (b) numerical data. (Parameters are as in Fig. 3.)Reuse & Permissions