Abstract
Advanced quantum technologies, as well as fundamental tests of quantum physics, crucially require the interference of multiple single photons in linear-optics circuits. This interference can result in the bunching of photons into higher Fock states, leading to a complex bosonic behavior. These challenging tasks timely require to develop collective criteria to benchmark many independent initial resources. Here we determine whether n independent imperfect single photons can ultimately bunch into the Fock state | n ⟩ . We thereby introduce an experimental Fock-state bunching capability for single-photon sources, which uses phase-space interference for extreme bunching events as a quantifier. In contrast to autocorrelation functions, this operational approach takes into account not only residual multi-photon components but also a vacuum admixture and the dispersion of individual photon statistics. We apply this approach to high-purity single photons generated from an optical parametric oscillator and show that they can lead to a Fock-state capability of at least 14. Our work demonstrates a novel collective benchmark for single-photon sources and their use in subsequent stringent applications.
Highlights
Beyond its fundamental significance, the Hong–Ou–Mandel (HOM) effect [1], where two single photons interfere on a beam splitter, has been central to the development of quantum technologies
We show that the Fock state capability nonlinearly decreases with photon loss, providing a more stringent characterization than g (2)(0), which is independent of photon loss, and more than the negative Wigner function that decreases only linearly
Our results indicate that despite the negative impact of multi-photon contributions typically reported using g (2)(0), they prevent the bunching of single-photon states into a respective Fock state less severely than optical loss
Summary
The Hong–Ou–Mandel (HOM) effect [1], where two single photons interfere on a beam splitter, has been central to the development of quantum technologies. The elementary example is the appearance of the Fock state |2 based on the HOM effect, as demonstrated in experiments with optical photons and with microwave photons [16,36], phonons in trapped ions [37], or surface plasmons [38,39] This extreme bunching event, i.e., the result of a clear operational procedure, enables to introduce a strong benchmark for single-photon states that evaluates their ability to undergo multi-photon interference [40]. This Fockstate bunching capability relies on negativities of the resulting Wigner function that provide a very sensitive signature of the non-classicality of the generated higher Fock states [41,42]. Our results indicate that despite the negative impact of multi-photon contributions typically reported using g (2)(0), they prevent the bunching of single-photon states into a respective Fock state less severely than optical loss
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