Method of Operating a Semiconductor Spin Qubit Quantum Computer

Vladimir Privman A, Dima Mozyrsky, Israel D. Vagner

Alexander Ivlev, Damien R. Crielaard, Marcel Meyer +8 more

Semiconductor spin qubits have emerged as a promising platform for quantum computing, following a significant improvement in their control fidelities over recent years. Increasing the qubit count remains challenging, beginning with the fabrication of small features and complex fan-outs. A particular challenge has been formed by the need for individual barrier gates to control the exchange interaction between adjacent spin qubits. Here, we propose a method to vary two-qubit interactions without applying pulses on individual barrier gates while also remaining insensitive to detuning noise in first order. Experimentally we find that changing plunger gate voltages over 300 mV can tune the exchange energy J from 100 kHz to 60 MHz. This allows us to perform two-qubit operations without changing the barrier gate voltage. Based on these findings we conceptualize a spin qubit architecture without individual barrier gates, simplifying the fabrication while maintaining the control necessary for universal quantum computation.

Hans A. De Raedt, Kristel F. L. Michielsen, Anthony Hams +2 more

Qi-Pei Liu, Zheng‐Yuan Xue

Scalable quantum computation demands high-fidelity two-qubit gates. However, decoherence and control errors are inevitable, which can decrease the quality of implemented quantum operations. We propose a robust iswap gate protocol for semiconductor spin qubits, which is a promising platform for scalable quantum computing. Our scheme uses only local microwave drives on conventional exchange-coupled spin qubits. This approach simultaneously addresses two critical challenges to semiconductor quantum computing: It suppresses low-frequency noise via continuous dynamical decoupling, and it circumvents the control difficulties associated with the ac modulation of the exchange interaction. We further develop a composite pulse sequence to remove drive-strength constraints and a dynamically corrected method to provide first-order immunity to microwave amplitude errors. Numerical simulations confirm that our scheme can achieve fidelity above the fault-tolerance threshold under current experimental conditions, offering a building block for practical quantum processors.

Anasua Chatterjee, Paul Stevenson, Silvano De Franceschi +3 more

Tim Botzem, Michael Shulman, Arne Ludwig +13 more

We present efficient methods to reliably characterize and tune gate-defined semiconductor spin qubits. Our methods are developed for double quantum dots in GaAs heterostructures, but they can easily be adapted to other quantum-dot-based qubit systems. These tuning procedures include the characterization of the interdot tunnel coupling, the tunnel coupling to the surrounding leads, and the identification of various fast initialization points for the operation of the qubit. Since semiconductor-based spin qubits are compatible with standard semiconductor process technology and hence promise good prospects of scalability, the challenge of efficiently tuning the dot’s parameters will only grow in the near future, once the multiqubit stage is reached. With the anticipation of being used as the basis for future automated tuning protocols, all measurements presented here are fast-to-execute and easy-to-analyze characterization methods. They result in quantitative measures of the relevant qubit parameters within a couple of seconds and require almost no human interference.