Photon antibunching quantum field correlations

Figure 10. Illustration of eight different predictions of photon antibunching of quantum fields, corresponding to the cases analyzed in Table III and Fig. 9. The two-time signal-mode correlation functions Agi(t,t + x) (dashed curves), Agn(t,t + t) (dot-dashed), and Agni(M + f) (solid) are plotted in their dependence on the rescaled time separation kt for fixed values of the evolution time (case 1) Kt = 2.8, (2) kt = 2.6, (3) kt = 0.1, (4) kt = 0.1, (5) Kt = 1.0, (6) kt = 2.3, (7) Kt = 0.7, and (8) Kt — 1.8. Signal and idler modes are initially in Fock states with Na — 3 and Nt, = 1 in cases 2 and 3, or with Na —2 and Nb — 1 in all other cases.

Turning now to the nanosecond time regime (lower half of Fig. 11), the emitted photons from a single molecule can provide still more useful information. On the time scale of the excited state lifetime, the statistics of photon emission from a single quantum system are expected [84] to show photon antibunching, which means that the photons space themselves out in time , that is, the probability for two photons to arrive at the detector at the same time is small. This is a uniquely quantvun-mechanical effect, which was first observed for Na atoms in a low-density beam [85]. Antibunching is fundamentally measured by computing the second-order correlation of the electric field (r) (whieh is simply the normalized form of the intensity-... 

In conclusion, we have presented the Hrst high-resolution heterodyne measurement of the elastic peak in resonance fluorescence of a single ion. At identical experimental parameters we have also measmed antibunching in the photon correlation of the scattered Held. Together, both measurements show that, in the limit of weak excitation, the fluorescence light differs from the excitation radiation in the second-order correlation but not in the first order correlation. However, the elastic component of resonance fluorescence combines an extremely narrow frequency spectrum with antibunched photon statistics, which means that the fluorescence radiation is not second-order coherent as expected from a classical point of view. This apparent contradiction can be explained easily by taking into accoimt the quantum nature of light, since first-order coherence does not imply second-order coherence for quantized fields (19). The heterodyne and the photon correlation measurement are complementary since they emphasize either the classical wave properties or the quantum properties of resonance fluorescence, respectively. 

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