Researchers achieve record quantum entanglement with 14 photons at once

This will be very useful in progressing the field of quantum computers and communication.
Ameya Paleja
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A single rubidium atom is trapped in an optical resonator consisting of two highly reflective mirrors. Repeated excitation of the atom causes several entangled single photons to be emitted in succession.

Max Planck of Quantum Optics 

Researchers at the Max Planck Institute of Quantum Optics set a new record after achieving a quantum entanglement of 14 photons, the largest on record so far, an institutional press release said.

Quantum entanglement, famously described by Albery Einstein as "spooky action at a distance" is a phenomenon where particles become intertwined in such a way that they cease to exist individually, and changing the specific property of one results in an instant change of its partner, even if it is far away.

Even though science fails to explain this, experiments successfully demonstrate that quantum entanglement exists and has now even become the basis of upcoming technologies like quantum computing, where entangled particles are used to store and process information. Following computing parlance, these are called quantum bits or qubits.

Quantum entangling photons

Scientists have previously managed to entangle trillions of atoms of gas. While this might be useful to demonstrate the phenomenon, it cannot be used for purposes of computing where a more controlled entanglement is required.

Researchers at the Max Planck Institute of Quantum Optics, therefore, set about to achieve this. They placed a single rubidium atom in an optical cavity so that it be bombarded with light particles and bounce off electromagnetic waves. When the atom was struck by a laser at a particular frequency, it prepared it to have a certain property. Then a separate control pulse was beamed at it, which caused it to emit a photon that was entangled with the atom.

The process was then repeated until a whole chain of photons was produced that were all entangled with each other. Between each emission, the atom was rotated which helped in the entangling of the 14 photons, the press release said.

The researchers claim not only claim that this is the largest number of photons entangled with an atom in a laboratory but also that it is the most efficient process developed so far, with a 43 percent source-to-detection efficiency.

In plain speak, it means that for every second push of the button to fire a laser, the researchers were able to generate, one photon of light that could be used for a specific application. This has solved the long-standing obstacle on the path of scalable, measurement-based quantum computing, the researchers claim.

Where will this help?

The quantum entanglement of 14 photons generated using this method may seem too low when compared to other methods. However, photons created on those methods are generated randomly and cannot be bundled. Since a single atom was used by the researchers in this method, they can produce photons in a highly deterministic way, which is necessary for quantum applications.

Apart from quantum computing, the research can also help in advancing quantum communication, where information sent through optic fiber won't be prone to tapping. The method developed by the researchers will allow quantum information to be sent over entangled photons, which will not only survive certain amounts of light loss but also secure communication, the press release said.

The researchers are now working to generate photons from two atoms to take their work forward.

The results of the study were published in the journal Nature.

Abstract

The central technological appeal of quantum science resides in exploiting quantum effects, such as entanglement, for a variety of applications, including computing, communication, and sensing1. The overarching challenge in these fields is to address, control and protect systems of many qubits against decoherence2. Against this backdrop, optical photons, naturally robust and easy to manipulate, represent ideal qubit carriers. However, the most successful technique so far for creating photonic entanglement3 is inherently probabilistic and, therefore, subject to severe scalability limitations. Here we report the implementation of a deterministic protocol4,5,6 for the creation of photonic entanglement with a single memory atom in a cavity7. We interleave controlled single-photon emissions with tailored atomic qubit rotations to efficiently grow Greenberger–Horne–Zeilinger (GHZ) states8 of up to 14 photons and linear cluster states9 of up to 12 photons with a fidelity lower bounded by 76(6)% and 56(4)%, respectively. Thanks to a source-to-detection efficiency of 43.18(7)% per photon, we measure these large states about once every minute, which is orders of magnitude faster than in any previous experiment3,10,11,12,13. In the future, this rate could be increased even further, the scheme could be extended to two atoms in a cavity14,15, or several sources could be quantum mechanically coupled16, to generate higher-dimensional cluster states17. Overcoming the limitations encountered by probabilistic schemes for photonic entanglement generation, our results may offer a way toward scalable measurement-based quantum computation18,19 and communication20,21.

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