Abstract
High-bit-rate long-distance quantum communication is a proposed technology for future communication networks and relies on high-dimensional quantum entanglement as a core resource. While it is known that spatial modes of light provide an avenue for high-dimensional entanglement, the ability to transport such quantum states robustly over long distances remains challenging. To overcome this, entanglement swapping may be used to generate remote quantum correlations between particles that have not interacted; this is the core ingredient of a quantum repeater, akin to repeaters in optical fibre networks. Here we demonstrate entanglement swapping of multiple orbital angular momentum states of light. Our approach does not distinguish between different anti-symmetric states, and thus entanglement swapping occurs for several thousand pairs of spatial light modes simultaneously. This work represents the first step towards a quantum network for high-dimensional entangled states and provides a test bed for fundamental tests of quantum science.
Highlights
Background subtractionExpected four-way coincidence: Consider a laser with a repetition rate of R pumping a nonlinear crystal to generate an entangled photon pair A and B via detected betweenspontaneous parametric downconversion (SPDC)
The first pair is an entangled state shared by Alice (A) and Bob (B); the second pair is an entangled state shared by Charlie (C) and Daisy (D)
We generate entangled photons using SPDC in 1-mm-thick β-barium borate (BBO) crystals
Summary
Background subtractionExpected four-way coincidence: Consider a laser with a repetition rate of R pumping a nonlinear crystal to generate an entangled photon pair A and B via detected betweenSPDC. Expected four-way coincidence: Consider a laser with a repetition rate of R pumping a nonlinear crystal to generate an entangled photon pair A and B via detected between. Consider the same laser pulse pumping a second crystal to generate a second pair of photons. The probability to detect/generate these two uncorrelated photon pairs from the same laser pulse, with one pair detected at detectors A and B and the other at C and D, is given by CA′ BCC′ D R2 ð9Þ. In our experiment a photon pair generated by BBO1 can be detected in coincidence by detectors A&B or A&C, and a second pair generated by BBO2 can be detected by detectors B&D or C&D, so we add all the combinations that can result in coincidence between all four detectors. The number of four-way coincidence events per second detected from two entangled photon pairs is C4′ W ÀCA′ B CC′ D
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