Steady-state Entanglement of Spin Qubits Via Chiral Magnons Achieves Coupling over Microns

The pursuit of stable quantum connections between distant qubits represents a significant challenge in building powerful quantum technologies, and researchers are now exploring innovative methods to achieve this crucial link. Martijn Dols, Mikhail Cherkasskii, and colleagues, including Victor A. S. V. Bittencourt, Carlos Gonzalez-Ballestero, Durga B. R. Dasari, and Silvia Viola Kusminskiy, demonstrate a promising approach using magnons, wave-like excitations in magnetic materials, to create and sustain entanglement between spin qubits. This team proposes a hybrid system where specially engineered magnons mediate a unidirectional coupling between qubits, driving them towards a maximally entangled state, and importantly, they have benchmarked a protocol accounting for real-world limitations like qubit decay and dephasing. Their numerical tests, utilising nitrogen-vacancy centres coupled to magnetic films, reveal that qubit dephasing currently limits the distance over which this stable entanglement can be maintained, but also pinpoint the necessary technological advancements to extend these connections over several microns, paving the way for robust, long-range quantum communication and computation using magnonic networks.

The study focuses on magnons exhibiting non-reciprocity and chirality, properties that allow for unidirectional propagation and a defined sense of rotation, respectively. These characteristics are crucial for establishing robust and directional qubit interactions, minimizing decoherence and enhancing entanglement fidelity. The team demonstrates that carefully engineered magnon modes can facilitate sustained entanglement, even in the presence of environmental noise, offering a pathway towards scalable quantum information processing.

Scientists have developed a hybrid quantum system where a magnetic material supporting non-reciprocal or chiral magnons mediates the coupling of spin qubits. The team drives the qubits to establish a steady state, resulting in a maximally entangled Bell state, and devised a protocol benchmarked considering qubit decay and dephasing. This method involves carefully controlling the interactions between the qubits and the magnons, allowing for the creation and maintenance of entanglement, and offers a pathway towards robust quantum information processing as the unidirectional coupling helps protect the entangled state from environmental noise.

Spin Qubits and Quantum Coherence Studies

Current research reveals a strong focus on quantum information, materials science, and spintronics, with key themes including quantum computing and spin qubits utilizing nitrogen-vacancy (NV) centers in diamond due to their relatively long coherence times and potential for scalability. Research also explores quantum memory using rare-earth-doped antiferromagnets and yttrium iron garnet (YIG), and investigates entanglement purification and remote quantum registers to build quantum networks, with a central focus on protecting qubits from decoherence through dynamical decoupling and quantum jumps.

Spintronics and magnonics represent a significant secondary theme, with numerous studies dealing with spin waves, their generation, propagation, and manipulation. YIG is a key material, explored for its low damping and potential for long-distance spin wave propagation, and achieving non-reciprocal propagation of spin waves is a recurring theme, crucial for building isolators and circulators essential for quantum circuits. The use of exceptional points to enhance sensing and control is also under investigation.

Materials science plays a vital role, with research exploring van der Waals magnets with tunable chiral symmetry and heterostructures combining different materials to create novel functionalities. Quantum sensing, utilizing spin qubits for detecting magnetic and electric fields, is a key application, and these areas are converging to create hybrid quantum systems, such as integrating NV centers with YIG for long-distance quantum communication or combining NV centers with 2D materials to enhance coherence times.

Current research emphasizes the development of long-lived quantum memories, exploring topological protection to shield quantum information from decoherence, and utilizing exceptional points to enhance sensing, control, and non-reciprocity. Exciting areas for future work include scalable quantum networks based on NV centers and magnonics, on-chip quantum circuits based on magnonics, hybrid quantum memories, topological quantum computing with magnonic materials, quantum sensing with enhanced sensitivity, and exploiting exceptional points for quantum control and sensing.

This collection of research demonstrates a growing interest in hybrid quantum systems, non-reciprocal magnonics, and the development of scalable quantum technologies, with a noteworthy emphasis on materials science and the integration of different quantum platforms suggesting promising avenues for future advancements in quantum information science.

Magnons Sustain Long-Distance Qubit Entanglement

This research demonstrates a new method for coupling spin qubits using magnons to achieve a stable, maximally entangled state. Scientists have developed a hybrid system where qubits interact via these magnons, enabling a unidirectional coupling crucial for maintaining the quantum link between them. Through detailed modelling, the team shows that this approach can facilitate entanglement over distances exceeding microns, a significant step towards scalable quantum technologies.

The work identifies qubit dephasing as a key limitation, but the results confirm the viability of using magnonic networks to establish and sustain entanglement between solid-state spins over relatively long distances. The team benchmarked the protocol, considering factors like qubit decay and dephasing, and successfully demonstrated the potential for creating a robust quantum connection, expanding the toolkit available for quantum information processing and opening avenues for exploring alternative materials and platforms for building future quantum devices.

The authors acknowledge that qubit dephasing currently limits the achievable entanglement distance, and future work will focus on mitigating this effect, suggesting that the principles demonstrated could be extended to other qubit types and materials, offering a versatile pathway for developing advanced quantum technologies.