Quantum data stored in a trapped-ion network with strong memory capacity


The University of Oxford's quantum network component "Alice." A single photon entangled with a strontium ion confined inside the vacuum chamber is collected by an objective lens. David Nadlinger is credited.

The University of Oxford researchers have successfully developed a resilient quantum memory in a node of a trapped-ion quantum network. This groundbreaking memory design was published in a Physical Review Letters paper and is believed to be capable of storing information for prolonged periods despite continuous network activity.

According to Peter Drmota, a researcher involved in the study, "We are creating a network of quantum computers that use trapped ions to hold and process quantum data. To link quantum processing devices, we use single photons released by an atomic ion and harness quantum entanglement between this ion and the photons."

Trapped ions, which are charged atomic particles confined in space using electromagnetic fields, are a popular medium for realizing quantum computations. Meanwhile, photons, or particles of light, are typically employed to transmit quantum data between distant nodes. Drmota and his team have been exploring the possibility of integrating trapped ions with photons to produce more powerful quantum technologies.

According to a recent report in Physical Review Letters, researchers at the University of Oxford have designed a highly robust quantum memory in a trapped-ion quantum network node. The research team, led by Peter Drmota, has been working on creating a network of quantum computers that can store and process quantum information. 

Scientists have used trapped ions to store quantum information and single photons to connect quantum processing devices. In the latest experiment, they combined the strengths of strontium ions and photons, and calcium ions' long-lasting memories, to generate high-quality entanglement between a strontium ion and a photon and store it in a nearby calcium ion. 

Creating a quantum memory in a network node is challenging because the memory must be durable against concurrent network activity. The research team achieved this by ensuring that the memory was extremely isolated from the network, while at the same time having a fast and reliable mechanism that couples the memory to the network when necessary.

View inside the vacuum chamber, where we use electric fields and lasers to capture strontium and calcium ions. David Nadlinger is responsible for the images.

Drmota and his team have developed a quantum memory using two different atomic species - strontium and calcium - to minimize crosstalk while establishing a network link. The mixed-species architecture allows for limited crosstalk and real-time error detection, as well as in-sequence cooling.

 To connect the network and the memory, they used mixed-species entangling gates. The coherence time is improved by using calcium-43, which has transitions that are insensitive to magnetic fields and eliminates errors due to magnetic field noise. Meanwhile, strontium-88 is ideal for generating photons for networking, but it is sensitive to magnetic field noise.

The researchers were able to prolong the entanglement between the memory ion and a photon by transferring quantum information from the sensitive strontium-88 to the robust calcium-43 in their mixed-species architecture. 

The researchers achieved over 10 seconds of entanglement preservation, which is at least 1000 times longer than the bare strontium ion and a photon. Moreover, the strontium ion can be reused to produce further entangled photons, while maintaining the fidelity of the entanglement between the memory and the previous photon, achieving robustness against network activity. This was accomplished by integrating multiple challenging techniques that were previously developed in separate setups over several years into a single experiment.

Dr. Peter Drmota and his team at the University of Oxford have created a quantum memory within a trapped-ion quantum network node that can store information for long periods of time despite ongoing network activity. 

The team combined the capabilities of calcium and strontium ions to create high-quality entanglement between a strontium ion and a photon and store this entanglement in a nearby calcium ion, achieving extreme isolation between the memory and the network. In initial tests, the quantum memory proved to be highly robust, preserving entanglement between a trapped ion and photon for at least 10 seconds.

 The team's demonstration of this quantum memory could be a significant milestone in realizing distributed quantum information processing and pave the way for scalable quantum computing systems.

Source: P. Drmota et al, Robust Quantum Memory in a Trapped-Ion Quantum Network Node, Physical Review Letters (2023). DOI: 10.1103/PhysRevLett.130.090803.


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