Abstract
Quantum mechanics implies that a single photon can be in the superposition of two distant spatial modes and enable nonlocal interferences. The most vivid example is the two-photon coalescence on a beam splitter, known as Hong-Ou-Mandel interference. In the past decade, this experiment has been used to characterize the suitability of different single-photon sources for linear optical quantum gates. This characterization alone cannot guarantee the suitability of the photons in a scalable quantum network. As for a deeper insight, we perform a number of nonclassical interference measurements of single photons emitted by a single organic molecule that are optimized by an atomic Faraday filter. Our measurements reveal near unity visibility of the quantum interference, and a one-port correlation measurement proves the ideal Fourier limited nature of our single-photon source. A delayed choice quantum eraser allows us to observe a constructive interference between the photons, and a Hong-Ou-Mandel peak is formed additionally to the commonly observed dip. These experiments comprehensively characterize the involved photons for their use in a future quantum Internet, and they attest to the fully efficient interaction of the molecular photons with a next subsequent quantum node. They can be adapted to other emitters and will allow us to gain insights to their applicability for quantum information processing. We introduce a quality number that describes the photon’s properties for their use in a quantum network; this states that effectively 97% of the utilized molecular photons can be used in a scalable quantum optical system and interact with other quantum nodes. The experiments are based on a hybridization of solid state quantum optics, atomic systems, and all-optical quantum information processing.
- Received 22 February 2018
- Revised 10 May 2018
DOI:https://doi.org/10.1103/PhysRevX.8.031026
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Single photons will be a crucial ingredient in future quantum networks. While past experiments have focused on the “indistinguishability” of the photons, we characterize the photon’s suitability in a number of sophisticated quantum interference experiments, which are enabled by the almost ideal spectral features of photons emitted by a single organic dye molecule.
When two identical photons impinge on a beam splitter, they leave the beam splitter at one common port. This is known as Hong-Ou-Mandel interference and is caused by the single-particle nature of the photons, together with their destructive interference in the output paths of the beam splitter. In addition to observing this effect in our setup, we monitor only a single output port. Then, all characteristic features vanish, and no correlations among simultaneous and subsequent photons exist.
Photons are commonly fed orthogonally polarized to the beam splitter, to determine the correlation signal when they cannot interfere. This inhibits their interference and renders them as classical particles. Still, we are able to regain the interference effect by using a so-called quantum eraser, since the detectors cannot tell where the photons originated. This shows that a Hong-Ou-Mandel setup can interfere constructively as well as destructively (which is more widely expected). Since the coherence time and the spontaneous emission time are relevant for this effect, the vanishing correlation proves that the photons are Fourier limited.
Our experiments comprehensively characterize the photons from a single dye molecule for their use in a future quantum Internet and attest to the efficient interaction of the photons with subsequent quantum nodes.