A team of international researchers has made a significant breakthrough in quantum information by integrating a zincblende InAs nanowire double-quantum dot with a high-quality resonator, resulting in strong spin-photon coupling. This development has previously only been achieved with weak spin-photon coupling. The team used deterministically grown wurtzite tunnel barriers to achieve quantum confinement in the nanowire. Their experiments allowed them to identify relevant spin states and measure spin decoherence rates and spin-photon coupling strengths. This research could have significant implications for scalable quantum information processing.
Strong Coupling Between Microwave Photon and Singlet-Triplet Qubit
A team of researchers, including J.H. Ungerer, A. Pally, A. Kononov, S. Lehmann, J. Ridderbos, P.P. Potts, C. Thelander, K.A. Dick, V.F. Maisi, P. Scarlino, A. Baumgartner, and C. Schönenberger, have made significant progress in the field of quantum information by integrating a zincblende InAs nanowire double-quantum dot with a high-quality resonator. This integration has resulted in strong spin-photon coupling, a development that has previously only been achieved with weak spin-photon coupling.
The team from the Department of Physics at the University of Basel, the Swiss Nanoscience Institute, Solid State Physics and NanoLund at Lund University, the Institute of Physics and Center for Quantum Science and Engineering at Ecole Polytechnique Fédérale de Lausanne, and the MESA Institute for Nanotechnology at the University of Twente, used deterministically grown wurtzite tunnel barriers to achieve quantum confinement in the nanowire.
Quantum Confinement and Spin States
The researchers’ experiments on even charge parity states and at large magnetic fields allowed them to identify the relevant spin states and measure the spin decoherence rates and spin-photon coupling strengths. They found an anticrossing between the resonator mode in the single photon limit and a singlet-triplet qubit with a spin-photon coupling strength of g2π1 3.94 MHz. This coherent coupling exceeds the resonator decay rate κ2π 198 02 MHz and the qubit dephasing rate γ2π 116 7 MHz, putting their system in the strong coupling regime.
Promising Candidates for Scalable Quantum Information Processing
Spin qubits in semiconductors are promising candidates for scalable quantum information processing due to long coherence times and fast manipulation. For the qubit readout circuit, quantum electrodynamics based on superconducting resonators allows a direct and fast measurement of qubit states and their dynamics.
Achieving Strong Coupling
The team demonstrated that the strong coupling regime between a singlet-triplet qubit and a single photon in a superconducting resonator can be reached. They achieved this strong coupling by carefully designing the resonator and by using a DQD defined by in-situ grown tunnel barriers in a semiconductor with a large spin-orbit interaction.
Device Characterization and Results
The resonator-qubit system of device A, including a false-colored SEM image of the crystal-phase defined NW DQD, was measured in a dilution refrigerator with a base temperature of 70 mK. The DQD forms in the 490 and 370 nm long zincblende segments, separated by 30 nm long wurtzite red tunnel barriers with a conduction band offset of 100 meV.
The researchers prepared the DQD in an even charge configuration in the many-electron regime, described by a two-electron Hamiltonian. They observed a characteristic honeycomb pattern of the charge stability diagram of a DQD. Using a capacitance model, they extracted the gate-to-dot capacitance.
An article titled “Strong coupling between a microwave photon and a singlet-triplet qubit” was published in Nature Communications on February 5, 2024. The research was conducted by a team of scientists including Jann Hinnerk Ungerer, Alessia Pally, A. Kononov, Sebastian Lehmann, Joost Ridderbos, Patrick P. Potts, Claes Thelander, Kimberly A. Dick, Ville F. Maisi, Pasquale Scarlino, A. Baumgärtner, and Christian Schönenberger. The article can be accessed through its DOI reference.
