Nonzero temperature effects on antibunched photons emitted by a quantum point contact out of equilibrium

Electrical current fluctuations in a single-channel quantum point contact can produce photons (at frequency omega close to the applied voltage Vxe/h) which inherit the sub-Poissonian statistics of the electrons. We extend the existing zero-temperature theory of the photostatistics to nonzero temperature T. The Fano factor F (the ratio of the variance and the average photocount) is < 1 for T < T(c) (antibunched photons) and > 1 for T > T(c) (bunched photons). The crossover temperature T(c)similar or equal to Delta omega xh/k(B) is set by the bandwidth Delta omega of the detector, even if h Delta omega < eV. This implies that narrow-band detection of photon antibunching is hindered by thermal fluctuations even in the low-temperature regime where thermal electron noise is negligible relative to shot noise.