Optical control of superconducting qubits using a photodiode array

Superconducting qubits are a leading platform for realizing fault-tolerant quantum computers. Recent years have shown a marked increase in the number of superconducting qubits hosted in quantum processing units (QPUs). However, the state-of-the-art still falls short by several orders of magnitude for practical applications^[1]. The passive heat load of the coaxial input and output lines already uses up a significant part of the cooling capacity of dilution refrigerators^[2], making this a bottleneck for further scaling of superconducting QPUs. By converting signals to the optical domain, coaxial lines can be replaced with optical fibers, which can reduce the passive heat load by more than three orders of magnitude^[3]. A fiber optic connection (optical link) between superconducting qubits and room-temperature control electronics, has been demonstrated^[4] using an electro-optic modulator and a single photodiode for up- and downconversion, respectively. In this presentation, we describe an optical link consisting of an off-the-shelf photodiode array and room-temperature control hardware. This optical link is then used to coherently control qubits. We show that by replacing coaxial input lines with these optical links, we can reduce the total heat load of the system. Together with recent demonstrations of optical readout of superconducting qubits^[4],[5],[6], this work represents a path towards all-optical control and readout of superconducting qubits, circumventing the discussed scaling bottlenecks towards fault-tolerant quantum computing.

[1] Alexeev, Y. et al. (2021), PRX Quantum 2, 017001

[2] Krinner, S. et al. (2019) EPJ Quantum Technol. 6, 2

[3] Lecocq, F. et al. (2021) Nature 591, 575–579

[4] van Thiel, T. et al. (2024) arXiv:2310.06026v3

[5] Delaney, R.D. et al. (2022) Nature 606, 489–493

[6] Arnold, G. et al. (2023) arXiv:2310.16817v1