We introduce a detuning-modulated composite pulses scheme for robust quantum information processing, suitable for integrated photonics.

The advance of quantum technologies has given rise to an immediate need for feasible methods for precise state preparation and accurate state transfer. In recent years, integrated photonic circuits have emerged as a strong contender for quantum information processing (QIP) hardware due to their scalability and on-chip integration capacity. However, unavoidable fabrication errors lead to a significant decrease in the fidelity of light transfer and limit their integration in QIP applications, where the admissible error is $10^{-4}$[1].

Historically, composite pulses (CPs) have proved to be a powerful tool to correct for control errors in cross-disciplinary fields including nuclear magnetic resonance, atomic physics and nonlinear optics. Yet, these solutions could not be implemented in integrated photonic and other physical systems characterized by real coupling parameters.

This research is the first to address this limitation and derive CPs for a wider variety of qubit architectures, including integrated photonic systems. Within the coupled mode approximation [2], a coupled waveguide system is analogous to a two-level atomic system. We utilize off-resonant detunings as the control parameters to derive a new family of CPs for high-fidelity population transfer within the quantum error threshold. We derive a general approach [3] for precise quantum population transfer by N-piece detuning-modulated composite pulses, with minimal pulse overhead, achieving high-fidelity broadband and robust population transfer even for N=2, which was considered impossible until now.

Our solution is inherently stable to various systematic parameters (coupling strength, pulse duration, phase jitter and detuning), and achieves fidelities well above the QIP gate error threshold within the temporal lifetime of the system. We believe that our method will be a cornerstone for high-fidelity quantum operations for QIP, and particularly for integrated photonic systems.

[1] M. Nielsen and I. Chuange, Quantum Computation and Quantum Information (Cambridge University Press, Cambridge, 2000).
[2] A. Yariv, IEEE J. Quantum Electronics 9, 9 (1973).
[3] E. Kyoseva, H. Greener and H. Suchowski, “Detuning-modulated composite pulses for high-fidelity robust quantum control”, Phys. Rev. A 100 (3), 032333 (2019).