Figure - PMC

Skip to main content

An official website of the United States government

Here's how you know

Here's how you know

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

View full-text article in PMC

. 2016 Jun 20;7:11985. doi: 10.1038/ncomms11985

Search in PMC
Search in PubMed
View in NLM Catalog
Add to search

Copyright © 2016, Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.

This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article's Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

PMC Copyright notice

(a,b) The sketch map and CCD (charge-coupled device) picture (scale bar, 250 μm) of the third sample, respectively. Two single photons with the same polarization are coupled to single-mode waveguides by two gratings, respectively. Then, they interference at the first BS (3-dB coupler) and generate a two-photon quantum NOON state, encoded on the path as . With a mode multiplexer, the state will be changed to . After propagation in the multi-mode waveguide for a distance of 30 μm, this transverse waveguide-mode NOON state is changed back to a path NOON state. Two-photon interference, or two-photon NOON state interference, is measured by using the second on-chip BS, as shown in e (red dots). Classical interference is also measured for comparison (black dots). We observe a raw interference visibility of 90.3±7.8% (94.0±8.2% with background subtraction) with a period approximately half of the classical interference. (c,d) are the sketch map and CCD picture (scale bar 250 μm) of the fourth sample, respectively. A quantum two-photon NOON state is generated by an on-chip BS and then converted between the three degrees of freedom (path, transverse waveguide mode and polarization). (f,g) HOM interference patterns between the two photons from TE and TM outputs of the sample, respectively. Error bar comes from the Poisson statistical distribution. The raw visibilities are 96.8±7.8% (98.2±7.9% with background subtraction) and 96.7±8.3% (98.3±8.5% with background subtraction), respectively. These results prove unambiguously the preservation of quantum coherence in the conversion of quantum-entangled state between different degrees of freedom. It should be noted that all the measurements of the HOM interference were performed on the path degree of freedom for the sake of simplification.

Inline graphic — (a,b) The sketch map and CCD (charge-coupled device) picture (scale bar, 250 μm) of the third sample, respectively. Two single photons with the same polarization are coupled to single-mode waveguides by two gratings, respectively. Then, they interference at the first BS (3-dB coupler) and generate a two-photon quantum NOON state, encoded on the path as . With a mode multiplexer, the state will be changed to . After propagation in the multi-mode waveguide for a distance of 30 μm, this transverse waveguide-mode NOON state is changed back to a path NOON state. Two-photon interference, or two-photon NOON state interference, is measured by using the second on-chip BS, as shown in e (red dots). Classical interference is also measured for comparison (black dots). We observe a raw interference visibility of 90.3±7.8% (94.0±8.2% with background subtraction) with a period approximately half of the classical interference. (c,d) are the sketch map and CCD picture (scale bar 250 μm) of the fourth sample, respectively. A quantum two-photon NOON state is generated by an on-chip BS and then converted between the three degrees of freedom (path, transverse waveguide mode and polarization). (f,g) HOM interference patterns between the two photons from TE and TM outputs of the sample, respectively. Error bar comes from the Poisson statistical distribution. The raw visibilities are 96.8±7.8% (98.2±7.9% with background subtraction) and 96.7±8.3% (98.3±8.5% with background subtraction), respectively. These results prove unambiguously the preservation of quantum coherence in the conversion of quantum-entangled state between different degrees of freedom. It should be noted that all the measurements of the HOM interference were performed on the path degree of freedom for the sake of simplification.