This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Quantum networks, systems that connect devices and allow them to exchange information encoded in the quantum states of particles, could enable more secure communications. To build these networks, physicists need to devise strategies that allow distant particles to share quantum states, preserving them long enough to perform calculations or enable communication between devices.
Researchers at the University of Oxford recently realized a quantum network with four qubits (i.e., units of quantum information) encoded in trapped ions distributed between two locations linked by optical fibers. This network, outlined in a paper published in Physical Review Letters, relied on electrically charged atoms held in place by electromagnetic fields, also known as trapped ions. "The work grew out of our efforts to build a quantum network in which each node can do more than create an entangled link to another node," Dr.
Gabriel Araneda, co-senior author of the paper, told Phys.org. "A useful network also needs to process and store quantum information locally. Different atomic species can offer different advantages, so we wanted to combine them within the same network and investigate whether we could control entanglement between them, including when they are in separate nodes." The main goal of the team's study was to combine operations performed on atoms at each node (i.e., a location containing qubits) in a network with connections between locations, to create a shared quantum state that involves several atoms.
To achieve this, the researchers used two groups of trapped ions connected by optical fibers. "Each node contains one strontium atomic ion and one calcium atomic ion," explained Dougal Main, first author of the paper. "We use the strontium ions to establish the link: each emits a photon, and the photons are brought together and measured at a central station." The term "entanglement" means that particles share a quantum state that cannot be described as independent states for each particle.
To establish entanglement between the two distant strontium ions in their network, Araneda and his colleagues performed a Bell-state measurement on the photons, or particles of light, emitted by the two ions. A particular pattern of photon detections signaled that the ions had become entangled. "We then used operations within each node to extend that entanglement to the calcium ions," said Main.
"In this way, we created entangled states involving three or four ions across the two nodes. To preserve entanglement for longer, we transferred it to calcium ions, whose chosen states are less sensitive to magnetic-field noise." The researchers' approach combines operations on ions at two distinct locations in their network with a light-based connection. This allowed them to realize a shared entangled quantum state that involved up to four ions of two different elements (i.e., strontium and calcium), distributed across the two locations.
Extract — continue reading at the source.
