Special Seminar
Name: Dr. Sagar Paul
Affiliation: Karlsruhe Institute of Technology (KIT), Germany
Title: “Single Molecule Magnets for Quantum Computation: Insights from Micro-SQUID-EPR”
Date & Time: Tuesday, 16th December at 11:00 a.m.
Venue: Rajarshi Bhattacharyya Memorial Lecture Hall, Chemical Sciences Buidling
Abstract:
Single-molecule magnets (SMMs) possess robust quantum states that can be reproducibly prepared and tuned by engineering magnetic anisotropy at the molecular level. These systems can exhibit ultraslow relaxation [1] and resonant quantum tunneling of magnetization (QTM), enabling a wide range of quantum applications [2]—from quantum sensing and memory to multilevel quantum bits (qudits) and fault-tolerant quantum computation. The hyperfine levels detected via micro-SQUID (M(H)) measurements and single-electron-spin-transistors, which enable nuclear spin-based quantum computation [3], along with observations of long decoherence times for electronic spin states in single-ion magnets [4], have reignited interest in these systems. A detailed mapping of the spin manifold in SMMs—via orientation and frequency scans—is vital for their integration into quantum technologies. The combined micro-SQUID-EPR technique [5] uniquely probes spin states by exciting single crystals with microwaves while simultaneously measuring magnetism (Scheme. 1). Using this method, M(H) loops recorded across the 30 mK–5 K range and under varying microwave frequencies reveal absorption peaks corresponding to specific spin transitions. Plotting these peak positions against RF frequency (0.1–40 GHz) and field orientation enables full reconstruction of the system’s spin Hamiltonian [5] and direct observation of anti-level crossings between spin states. The latter has recently enabled a spectroscopic pathway to directly visualize topologically quenched tunneling regimes—a manifestations of geometric phase in spin-systems, advancing prospects for holonomic, fault-tolerant quantum computation based on 4f-SMMs.
References:
1. “Ultraslow Relaxation of Toroidal State in Ferrotoroidal Dysprosium Complex”, J. Am. Chem. Soc. (10.1021/jacs.5c12742) (2025).
2. “Molecular spin qudits for quantum algorithms”, Chem. Soc. Rev., 47, 501 (2018).
3. “Operating Quantum States in Single Magnetic Molecules: Implementation of Grover’s Quantum Algorithm” Physical review letters 119, 187702 (2017).
4. “Molecular spins for quantum computation”, Nature Chemistry 11, 301 (2019).
5. “Direct determination of high-order transverse ligand field parameters via µSQUID-EPR in a Et4N[160GdPc2] SMM”, Nature Communications 14, 3361 (2023); doi: 10.1039/D5QI01387A.