Spin Qubits and Quantum Dot Circuits
Our research on gate-controlled quantum dots focuses on the experimental implementation of spin qubit arrays in various material systems with the aim of understanding fundamental interactions in solids and deriving applications in quantum simulations and quantum computing. Key resources include access to high-quality quantum materials, nanofabrication facilities (both in-house and external), and the ability to couple quantum dots locally via gate-voltage pulses and over larger distances via superconducting resonators.
We study spin qubits in several semiconductor material platforms to extend this research field toward larger and well-controlled qubit networks, as well as to investigate fundamental questions in condensed matter physics . For example, gallium-arsenide (GaAs) heterostructures allow us to study in great detail the dynamics of nuclear spins [2,3] and electron-electron correlations [4,5], whereas spin qubits made from isotopically-purified silicon-28 (28Si) display excellent coherence times and provide a natural quantum material platform compatible with industrial fabrication and engineering . To learn more about our involvement with quantum large-scale integration in silicon, visit the QLSI homepage.
Arrays of quantum dots not only provide a suitable platform for quantum computing, but can also simulate the mechanics of the tiniest building blocks of the universe. Indeed, quantum dots display discrete electronic states similar to quantum states of atoms and molecules, making it possible to accelerate the understanding of biochemical processes and, eventually, lead to the development of new medicine.
While all activities involve a fruitful collaboration between experimental physics and theory, we are also exploring synergies with computer science in optimization, automation, and machine learning [7,8]. This enables us to complement a deepening understanding of spin phenomena with increasing control complexity in larger and larger quantum-dot circuits.
Our experiments are performed in dilution refrigerators below 100 mK and in the presence of magnetic fields up to 6 T, exploiting high-frequency control and measurement techniques that may find applications in other research fields, for instance, Topological Quantum Systems.
 Chatterjee, A., Stevenson, P., De Franceschi, S., Morello, A., de Leon, N. P., & Kuemmeth, F. (2021). Semiconductor qubits in practice. Nature Reviews Physics, 3(3), 157–177. https://doi.org/10.1038/s42254-021-00283-9
 Notch filtering the nuclear environment of a spin qubit, F. K. Malinowski, F. Martins, P. D. Nissen, E. Barnes, M. S. Rudner, S. Fallahi, G. C. Gardner, M. J. Manfra, C. M. Marcus, F. Kuemmeth, Nature Nanotechnology 12, 16 (2016). https://doi.org/10.1038/nnano.2016.170
 Spectrum of the Nuclear Environment for GaAs Spin Qubits, F. K. Malinowski, F. Martins, Ł. Cywiński, M. S. Rudner, P. D. Nissen, S. Fallahi, G. C. Gardner, M. J. Manfra, C. M. Marcus, F. Kuemmeth, Phys. Rev. Lett. 118, 177702 (2017). https://doi.org/10.1103/PhysRevLett.118.177702
 Negative spin exchange in a multielectron quantum dot, F. Martins, F. K. Malinowski, P. D. Nissen, S. Fallahi, G. C. Gardner, M. J. Manfra, C. M. Marcus, F. Kuemmeth, Phys. Rev. Lett. 119, 227701 (2017). https://doi.org/10.1103/PhysRevLett.119.227701
 Spin of a multielectron quantum dot and its interaction with a neighboring electron, K. Malinowski, F. Martins, T. B. Smith, S. D. Bartlett, A. C. Doherty, P. D. Nissen, S. Fallahi, G. C. Gardner, M. J. Manfra, C. M. Marcus, F. Kuemmeth, Phys. Rev. X 8, 011045 (2018). https://doi.org/10.1103/PhysRevX.8.011045
 Ansaloni, F., Chatterjee, A., Bohuslavskyi, H., Bertrand, B., Hutin, L., Vinet, M., & Kuemmeth, F. (2020). Single-electron operations in a foundry-fabricated array of quantum dots. Nature Communications, 11(1), 6399. https://doi.org/10.1038/s41467-020-20280-3
 Estimation of Convex Polytopes for Automatic Discovery of Charge State Transitions in Quantum Dot Arrays, O. Krause, T. Rasmussen, B. Brovang, A. Chatterjee, F. Kuemmeth, arXiv:2108.09133 (2021). https://arxiv.org/abs/2108.09133
 Chatterjee, A., Ansaloni, F., Rasmussen, T., Brovang, B., Fedele, F., Bohuslavskyi, H., Krause, O., & Kuemmeth, F. (2021). Autonomous estimation of high-dimensional Coulomb diamonds from sparse measurements. ArXiv:2108.10656 [Cond-Mat]. http://arxiv.org/abs/2108.10656
 Fedele, F., Chatterjee, A., Fallahi, S., Gardner, G. C., Manfra, M. J., & Kuemmeth, F. (2021). Simultaneous Operations in a Two-Dimensional Array of Singlet-Triplet Qubits. PRX Quantum, 2(4), 040306. https://doi.org/10.1103/PRXQuantum.2.040306
 Fast Charge Sensing of Si/SiGe Quantum Dots via a High-Frequency Accumulation Gate, C. Volk, A. Chatterjee, F. Ansaloni, C. M. Marcus, F. Kuemmeth, Nano Letters 19, 5628 (2019). https://doi.org/10.1021/acs.nanolett.9b02149
 Fast spin exchange across a multielectron mediator, F. K. Malinowski, F. Martins, T. B. Smith, S. D. Bartlett, A. C. Doherty, P. D. Nissen, S. Fallahi, G. C. Gardner, M. J. Manfra, C. M. Marcus, F. Kuemmeth, Nature Communications 10, 1196 (2019). https://doi.org/10.1038/s41467-019-09194-x
 Symmetric Operation of the Resonant Exchange Qubit, F. K. Malinowski, F. Martins, P. D. Nissen, S. Fallahi, G. C. Gardner, M. J. Manfra, C. M. Marcus, F. Kuemmeth, Phys. Rev. B 96, 045443 (2017). https://doi.org/10.1103/PhysRevB.96.045443