The future quantum internet is built on quantum memories. It would be difficult to transmit quantum information over long distances without them. The purpose of these memories is to receive the quantum information in a photon and then store it and retrieve it. Cold atoms or doped crystals can be used to realize quantum memories.
To ensure the quality of quantum communication, they need to fulfill several requirements, such as the efficiency, duration, and multiplexing of their storage capability. Design of quantum memories that can be directly integrated in the fiber-optic network is one of the requirements.
With the boom of quantum technologies, a lot of work has been done to make existing quantum memories smaller and simpler to use in a real work network. Finding a solution that preserves good coherence properties, as well as the miniaturization of the control system of the quantum memory and its interface, are some of the hurdles that come with a fully integrated approach. All of this should be done in the same way as in the standard bulk versions of the device. The current realization of fiber-integrated quantum memories is far from what can be achieved in bulk memories.
The objectives have been clear in a recent work published in Science Advances.
There is a quantum memory.
The team used a crystal to make their quantum memory. The memory was written on with a laser. The photon is guided by a canal within the crystal. Two identical optical fibers were attached to both sides of the crystal to provide a direct interface between photon and memory An all fiber connection was made between the quantum memory and a source of light.
The team used a source of entangled photon pairs where one photon is compatible with the memory and the other one is at the telecom wavelength. They were able to store photon pairs from 2 to 28 s and preserve their integrity. The result obtained is a major improvement because the team shows that the device is 1000 times longer than any other fiber-integrated device used until now.
Thanks to the fully integrated nature of the device, a more sophisticated control system was able to be used. The team proved that the system is compatible with telecommunications infrastructure and suitable for long-distance quantum communication because of the visible photon shared between the quantum memory and the telecom wavelength.
The demonstration of integrated quantum memory opens up a lot of possibilities. According to Jelena Rakonjac, "this experiment has given us great hopes in the sense that we envision that many waveguides can be fabricated in one crystal, which would allow for many photons to be stored simultaneously in a small region and maximize the capabilities of the quantum memory." The device can be interfaced with other fiber based components since it is already fiber coupled.
"We are thrilled with this result which opens a lot of possibilities for fiber integrated memories," said de Riedmatten. The way in which this material is created allows us to perform close to bulk memories. Extending the storage to spin states will allow on-demand retrieval of the stored photon and lead to long storage times. The fiber-integrated quantum memory is very promising for use in quantum networks.
More information: Jelena V. Rakonjac et al, Storage and analysis of light-matter entanglement in a fiber-integrated system, Science Advances (2022). DOI: 10.1126/sciadv.abn3919 Journal information: Science Advances
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