Observing the quantum behavior of light in an undergraduate laboratory

Abstract

While the classical, wavelike behavior of light (interference and diffraction) has been easily observed in undergraduate laboratories for many years, explicit observation of the quantum nature of light (i.e., photons) is much more difficult. For example, while well-known phenomena such as the photoelectric effect and Compton scattering strongly suggest the existence of photons, they are not definitive proof of their existence. Here we present an experiment, suitable for an undergraduate laboratory, that unequivocally demonstrates the quantum nature of light. Spontaneously downconverted light is incident on a beamsplitter and the outputs are monitored with single-photon counting detectors. We observe a near absence of coincidence counts between the two detectors—a result inconsistent with a classical wave model of light, but consistent with a quantum description in which individual photons are incident on the beamsplitter. More explicitly, we measured the degree of second-order coherence between the outputs to be g(2)(0)=0.0177±0.0026, which violates the classical inequality g(2)(0)⩾1 by 377 standard deviations.

First quantized electrodynamics

“…That is, owing to the Cauchy-Schwarz inequality, the correlation of intensity for classical beams must be greater than unity. Correlations less than unity are routinely observed [32] at very low levels of illumination, and such antibunching can be explained [27] with QTR. It appears that only QTR can explain the sub-Poisson statistics which are detected again in very weak light beams [27].…”

Uma abordagem conceitual e fenomenológica dos postulados da física quântica

“…onde é a constante de Planck e a frequência da luz (GRANGIER et al, 1986;THORN et al, 2004;GALVEZ et al, 2005), ou seja, são, de fato, quanta de energia.…”

Quantum Plasmonics: From Quantum Statistics to Quantum Interferences

“…Additionally, these accidental coincidences lead to a value of g (2) (0) higher than zero. One can show [74] that the offset on g (2) (0) due to accidental coincidences is:…”

“…This plot shows the vital role of the detection of photons in mode A for the conditional measurements of the statistics of the out-coupled light from the waveguides. Without this 'heralding' of the photons, the statistics of the light arriving at the detectors are those of a thermal field [74]. It should be noted that the theoretically expected peak of g (2) c (0)=2 for a thermal field is challenging to observe in quantum optics experiments [82], as instead of reaching the value of 2, its height above unity is effectively proportional to the ratio of the coherence time of the singlephoton source to the response time of the detection, which in our experiment is ≈ 10 −5 .…”