Abstract
As superconducting quantum circuits scale to larger sizes, the problem of frequency crowding proves a formidable task. Here we present a solution for this problem in fixed-frequency qubit architectures. By systematically adjusting qubit frequencies post-fabrication, we show a nearly tenfold improvement in the precision of setting qubit frequencies. To assess scalability, we identify the types of “frequency collisions” that will impair a transmon qubit and cross-resonance gate architecture. Using statistical modeling, we compute the probability of evading all such conditions, as a function of qubit frequency precision. We find that, without post-fabrication tuning, the probability of finding a workable lattice quickly approaches 0. However, with the demonstrated precisions it is possible to find collision-free lattices with favorable yield. These techniques and models are currently employed in available quantum systems and will be indispensable as systems continue to scale to larger sizes.
Highlights
Realizing robust large-scale quantum information processors is one of the foremost challenges in quantum science
Many practical applications have been proposed for robust quantum computers, including estimating the ground state energy of chemical compounds and implementing machine learning algorithms[1,2,3,4,5,6,7,8]
Degeneracies among the j0i ! j1i, j1i ! j2i, and j0i ! j2i transitions of nearby qubits can all contribute to frequency collisions
Summary
Realizing robust large-scale quantum information processors is one of the foremost challenges in quantum science. Quantum advantage relative to classical computers can be realized without full fault tolerance, but requires large quantum circuits that a classical computer cannot simulate[9]. Recent demonstrations have shown qubit circuits nearly at the threshold for demonstrating quantum advantage[10]. Much work remains in order to realize fault-tolerant quantum processors; scaleup of solid-state quantum circuits has shown consistent and ongoing progress[11,12,13,14,15,16,17,18,19,20]. Fixed-frequency transmons are largely insensitive to charge or flux noise and have achieved coherence times of 100 μs and growing. High on the list of such challenges is the issue of “frequency crowding.”
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