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Sensing Single Spins in Dense Spin Baths

Published on May 12th, 2020

The detection of an external single nuclear spin in a noisy spin environment opens up new possibilities for future quantum technologies.

A team of researchers from the University of Stuttgart, Germany, in collaboration with Beijing Computational Science Research Center, China, have been able to detect an external single silicon-29 (29Si) nuclear spin using  the electron spin of a rare-earth ion, located in a dense nuclear-spin bath of yttrium orthosilicate (Y2SiO5 or YSO).

When trying to implement quantum systems in quantum communications, isolated systems are essential to prevent any kind of decoherence, that is, the destruction of the quantum state. Nuclear spins have shown to be very small sizes, have small magnetic moments and are more isolated than electron spins. Hence, these properties enable these systems to have longer coherence times, something much needed and very valued for storing quantum information.

On the other hand, rare-earth related electron spins in crystals are ideal elements for quantum information, because they can interact with nuclear spins in their environment and be used as valuable quantum memory resources. But, so far, the detection of environmental/nearby/etc nuclear spins, and in particular single environmental/nearby/etc nuclear spins, had only been achieved in dilute material systems, such as few dilute nuclear spin bath host systems, like nitrogen-vacancy center in diamond or the silicon vacancy in silicon carbide. Thus, the detection of nearby individual nuclear spins remained a challenge for rare-earths in their host materials.

In the work recently published in Physical Review Letters, the team of scientists has opened the door to quantum memory applications in rare-earth ion related systems, potentially useful for quantum error correction schemes.

The researchers used a YSO crystal, holding a 5% of 29Si single nuclear spins, to investigate the nuclear environment of individual rare-earth Ce3+ electron spins. In their experiment, they first used circularly polarized laser pulses to excite individual Ce3+-related electron spins into a specific spin state. By using a microwave field, they were able to control the spin state of the rare-earth element and by driving it into a superposition state, they were able to detect nearby nuclear spins from 29Si. The team found that these 29Si nuclear spins could be detected for about 20% of Ce3+ ions where 29Si nuclear spin is the nearest lattice neighbour.

The results of the study prove that single 29Si nuclear spins, located within a dense crystal structure, could be detected, and potentially initialized and used as quantum memories. Additionally, the use of a rare-earth Ce3+ sensor spin and their interaction with the nuclear spins can enable active quantum processing, such as quantum error correction. They have shown that these systems could be incorporated into a large number of materials, enabling a wider range of materials accessible for future applications in quantum technologies. Such previously inaccessible materials could serve as valuable quantum memory resources, a key for building a quantum computer. They could also be used to build a quantum repeater, which will allow a secure transmission of citizen’s data.

The study has been conducted with funding from the Quantum Flagship’s SQUARE project. The SQUARE project is part of the basic science segment and aims at establishing a new platform for quantum computing, quantum networking and quantum communication. In particular, they want to show that rare earth ions in solids could serve as a material that allows high-density integration of the elementary building blocks of quantum computers – qubits – and their efficient local and long-range interconnection via light. To do so, they will demonstrate the basic elements of a multifunctional quantum processor node and develop scalable device elements.

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