High-Fidelity Entangling Gate for Double-Quantum-Dot Spin Qubits

January 26, 2017

Figure 1*. [Reprinted under a Creative Commons Attribution 4.0 International License.]

Electron spins in semiconductors are promising qubits because their long coherence times enable nearly 109 coherent quantum gate operations. However, developing a scalable high-fidelity two-qubit gate remains challenging. In a new npj Quantum Information article*, members of Prof. Amir Yacoby's group, including John Nichol, Lucas Orona and Shannon Harvey, together with colleagues from Purdue University, demonstrated an entangling gate between two double-quantum-dot spin qubits in GaAs by using a magnetic field gradient between the two dots in each qubit to suppress decoherence due to charge noise. When the magnetic gradient dominates the voltage-controlled exchange interaction between electrons, qubit coherence times increase by an order of magnitude. Using randomized benchmarking, the physicists measured single-qubit gate fidelities of ~99%, and through self-consistent quantum measurement, state, and process tomography, they measured an entangling gate fidelity of 90%. In the future, operating double quantum dot spin qubits with large gradients in nuclear-spin-free materials, such as Si, should enable a two-qubit gate fidelity surpassing the threshold for fault-tolerant quantum information processing.

*See John M. Nichol, Lucas A. Orona, Shannon P. Harvey, Saeed Fallahi, Geoffrey C. Gardner, Michael J. Manfra & Amir Yacoby, "High-fidelity entangling gate for double-quantum-dot spin qubits," npj Quantum Information 3 (2017) | doi:10.1038/s41534-016-0003-1