Abstract
Quantum repeaters are nodes in a quantum communication network that allow reliable transmission of entanglement over large distances. It was recently shown that highly entangled photons in so-called graph states can be used for all-photonic quantum repeaters, which require substantially fewer resources compared to atomic-memory-based repeaters. However, standard approaches to building multiphoton entangled states through pairwise probabilistic entanglement generation severely limit the size of the state that can be created. Here, we present a protocol for the deterministic generation of large photonic repeater states using quantum emitters such as semiconductor quantum dots and defect centers in solids. We show that arbitrarily large repeater states can be generated using only one emitter coupled to a single qubit, potentially reducing the necessary number of photon sources by many orders of magnitude. Our protocol includes a built-in redundancy, which makes it resilient to photon loss.
2 More- Received 29 January 2017
DOI:https://doi.org/10.1103/PhysRevX.7.041023
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
Quantum communication relies on the properties of quantum mechanics to provide inherent security to transmitted information. This information will be carried by quantum states of photons traveling via optical fibers. In classical telecommunications, repeaters are used to amplify signals at intermediate points so that the information can cover longer distances than what is possible with only optical fibers. Quantum repeaters have been suggested to play a similar role in quantum communication, but the nature of quantum states requires a distinct approach. It was recently shown that states of many photons with a specific type of entanglement can be used for all-photonic quantum repeaters. The generation of such states, however, remains probabilistic even in principle, limiting practical implementations. We provide a deterministic approach based on solid-state emitters which, when controlled appropriately, can generate photons readily in the required highly entangled “repeater” state.
We show that with only a single emitter coupled to one qubit, it is possible to generate repeater states with arbitrarily many photons. This is achieved by applying a particular sequence of operations between each photon emission event, including rotations and measurements on the emitter, and photon polarizations and entanglement operations between the emitter and qubit. These operations ensure that the emitted photons already carry the correct entanglement structure, bypassing the need for probabilistic photon manipulations.
Communication fidelity grows as the number of photons in the repeater state is increased, so the fact that only a single emitter is needed, regardless of photon number, is promising for scalability. Our approach thus constitutes a paradigm shift that could potentially reduce the resources needed to build a quantum communication network by orders of magnitude.