Real-time two-axis control of a spin qubit

Fabrizio Berritta; Torbjørn Rasmussen; Jan A Krzywda; Joost van der Heijden; Federico Fedele; Saeed Fallahi; Geoffrey C Gardner; Michael J Manfra; Evert van Nieuwenburg; Jeroen Danon; Anasua Chatterjee; Ferdinand Kuemmeth

doi:10.1038/s41467-024-45857-0

Real-time two-axis control of a spin qubit

Nat Commun. 2024 Feb 23;15(1):1676. doi: 10.1038/s41467-024-45857-0.

Authors

Fabrizio Berritta¹, Torbjørn Rasmussen², Jan A Krzywda³, Joost van der Heijden⁴, Federico Fedele², Saeed Fallahi^{5

6}, Geoffrey C Gardner⁶, Michael J Manfra^{5

6

7

8}, Evert van Nieuwenburg³, Jeroen Danon⁹, Anasua Chatterjee¹⁰, Ferdinand Kuemmeth^{11

12}

Affiliations

¹ Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100, Copenhagen, Denmark. fabrizio.berritta@nbi.ku.dk.
² Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100, Copenhagen, Denmark.
³ Lorentz Institute and Leiden Institute of Advanced Computer Science, Leiden University, P.O. Box 9506, 2300 RA, Leiden, The Netherlands.
⁴ QDevil, Quantum Machines, 2750, Ballerup, Denmark.
⁵ Department of Physics and Astronomy, Purdue University, West Lafayette, IN, 47907, USA.
⁶ Birck Nanotechnology Center, Purdue University, West Lafayette, IN, 47907, USA.
⁷ Elmore Family School of Electrical and Computer Engineering, Purdue University, West Lafayette, IN, 47907, USA.
⁸ School of Materials Engineering, Purdue University, West Lafayette, IN, 47907, USA.
⁹ Department of Physics, Norwegian University of Science and Technology, NO-7491, Trondheim, Norway.
¹⁰ Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100, Copenhagen, Denmark. anasua.chatterjee@nbi.ku.dk.
¹¹ Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, 2100, Copenhagen, Denmark. kuemmeth@nbi.dk.
¹² QDevil, Quantum Machines, 2750, Ballerup, Denmark. kuemmeth@nbi.dk.

Abstract

Optimal control of qubits requires the ability to adapt continuously to their ever-changing environment. We demonstrate a real-time control protocol for a two-electron singlet-triplet qubit with two fluctuating Hamiltonian parameters. Our approach leverages single-shot readout classification and dynamic waveform generation, allowing full Hamiltonian estimation to dynamically stabilize and optimize the qubit performance. Powered by a field-programmable gate array (FPGA), the quantum control electronics estimates the Overhauser field gradient between the two electrons in real time, enabling controlled Overhauser-driven spin rotations and thus bypassing the need for micromagnets or nuclear polarization protocols. It also estimates the exchange interaction between the two electrons and adjusts their detuning, resulting in extended coherence of Hadamard rotations when correcting for fluctuations of both qubit axes. Our study highlights the role of feedback in enhancing the performance and stability of quantum devices affected by quasistatic noise.