Spin-Qubit Relaxometry Detects Half-Vortex Magnetic Fluxes of ½ in Superconductors
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Researchers are now closer to realising topological quantum computation thanks to a new method for detecting half-quantum vortices in unconventional superconductors. Gábor B Halász, Nirjhar Sarkar, and Yueh-Chun Wu, from the Materials Science and Technology Division at Oak Ridge National Laboratory, alongside Joshua T Damron, Chengyun Hua, Benjamin Lawrie et al, have demonstrated a technique using spin-qubit relaxometry to directly measure the elusive half-integer magnetic flux carried by these vortices. This is significant because half-vortices are theorised to host Majorana zero modes, potentially offering a robust platform for building quantum bits less susceptible to environmental noise. By correlating spin-qubit relaxation rates with vortex crossing frequencies, the team provides a pathway to characterise these fundamental objects and advance the search for practical topological quantum materials like UTe₂, UPt₃, and URhGe. This is significant because half-vortices are theorised to host Majorana zero modes, potentially offering a robust platform for building quantum bits less susceptible to environmental noise. This innovative approach allows for the direct quantification of magnetic flux, distinguishing between conventional vortices carrying flux quantum Φ0 = h/(2e) and the half-quantum vortices predicted to exist in spin-triplet superconductors, which carry Φ0/2. The research establishes a clear experimental signature for identifying these elusive half-quantum vortices, potentially confirming the spin-triplet nature of the superconducting state. This is particularly relevant for candidate materials such as UTe2, UPt3, and URhGe, where definitive proof of spin-triplet pairing has remained challenging. Experiments show that the setup utilizes a thin-film type-II superconducting strip with constrictions designed to guide vortex movement. The work opens possibilities for utilizing quantum sensing with spin qubits to probe the fundamental properties of exotic superconductors. By analysing the magnetic field fluctuations induced by vortex dynamics, scientists can gain insights into the microscopic mechanisms governing superconductivity and potentially harness these systems for fault-tolerant quantum computation. This detailed analysis provides crucial guidance for optimising the experimental setup and maximising the sensitivity of the spin-qubit relaxometry technique. Vortex Detection via Spin Qubit Relaxometry Researchers positioned a spin qubit directly above this pinch point to monitor the resulting magnetic field fluctuations. By applying a bias current, vortices were nucleated at one constriction and directed towards another, ensuring consistent passage beneath the qubit at a predictable speed, v. Simulations revealed that the By and Bz components exhibit distinct behaviours dependent on the distance, d, between the qubit and the superconductor’s thickness, D. Specifically, calculations showed the magnetic field modulation, 4πλ²By(t) / Φ, and 4πλ²Bz(t) / Φ, varying with the ratio v t / D, where t represents time. Neighboring features are separated by a mean time difference of T, with a variation of τ ≪T, and the time t0 satisfying −T/2 t0 T/2. The dimensionless function G(α, Φf0/V) exhibits pronounced peaks at specific frequencies f0 = n/T, corresponding to integer multiples of a fundamental frequency 1/T, with peak width ∆f0 ∼n2τ 2/T 3. Tests prove that the sharpest peak occurs at the fundamental frequency, n = 1. However, for half-quantum vortices with Φ = Φ0/2, the fundamental voltage is reduced to V1 = Φ0f0/2 ≈3 μV. Measurements confirm that with reasonable parameters like D ∼100nm, v ∼104m/s, and λ ∼1μm, the relaxation time T1 = 1/Γ ≲1ms is resolvable with spin-qubit relaxometry. Half-vortex flux detection via spin-qubit relaxometry offers high The key finding is the potential to detect half-integer-quantized magnetic fluxes, specifically Φ0/2, which would strongly suggest the presence of spin-triplet superconductivity and half-quantum vortices supporting Majorana zero modes. The authors demonstrate that a relaxation time of approximately 1 millisecond is achievable and resolvable with current spin-qubit relaxometry techniques, given appropriate experimental parameters such as qubit distance. The proposed method is considered feasible for implementation in candidate spin-triplet materials including UTe2, UPt3, and URhGe. Future research directions could focus on optimising the experimental setup and exploring the behaviour of vortices in different spin-triplet materials. This work represents a significant step towards the direct observation of half-vortices and the verification of Majorana zero modes, which are crucial for advancing topological quantum computation. 👉 More information 🗞 Detecting half-quantum superconducting vortices by spin-qubit relaxometry 🧠 ArXiv: https://arxiv.org/abs/2601.19975 Tags: Rohail T. As a quantum scientist exploring the frontiers of physics and technology. My work focuses on uncovering how quantum mechanics, computing, and emerging technologies are transforming our understanding of reality. I share research-driven insights that make complex ideas in quantum science clear, engaging, and relevant to the modern world. 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