Adiabatic pulse shaping for capacitively coupled hybrid qubits and optimization of modular entangling sequences

Abstract

Implementation of logical entangling gates is an important step towards realizing a quantum computer. In this work, we theoretically examine the implementation of two-qubit logical entangling gates in noisy environments. We begin by using a gradient-based optimization approach to find single-qubit rotations which can be interleaved between applications of a noisy nonlocal gate to dramatically suppress arbitrary logical and leakage errors, while steering the evolution operator towards the perfectly entangling subset of SU(4) gates. The modularity of the approach allows for application to any two-qubit system, regardless of the Hamiltonian or details of the experimental implementation. This approach is effective for both quasi-static logical and leakage noise, as well as time-dependent 1/f logical noise. We then examine capacitive coupling between two quantum dot hybrid qubits, each consisting of three electrons in a double quantum dot, as a function of the energy detuning of the double dot potentials. We show that a shaped detuning pulse can produce a two-qubit maximally entangling operation in ?50ns without having to simultaneously change tunnel couplings. Simulations of the entangling operation in the presence of experimentally realistic charge noise yield two-qubit fidelities over 90%.