Characterizing and Mitigating Phononic and Photonic Poisoning in Solid-State Qubit
Abstract
Phononic and photonic poisoning mechanisms play a critical role in the operation of solid-state qubits. Poisoning due to impacts from high energy particles, such as gamma rays from background radioactivity and cosmic ray muons, results in offset-charge bursts and cascades of phonons capable of generating nonequilibrium QPs in superconductors. Light has also been shown to change the magnitude of low frequency noise in semiconductors at low temperature. In addition, mmwave photons from blackbody radiation generated in warmer parts of the cryostat that are not sufficiently filtered or shielded from the qubit are also a significant poisoning source for superconducting qubits. Besides suppressing the coherence of individual qubits, these mechanisms can also lead to correlated errors across qubit arrays, which are detrimental to current quantum error correction codes. Here we propose a comprehensive approach to characterize the spatial and temporal profile of poisoning events using both superconductor and semiconductor multi-qubit arrays, as well as alternative environmental sensors of poisoning energy depositions. Charge-sensitive transmon qubits will allow us to sense environmental offset-charge jumps in the substrate from the impact of ionizing radiation. We will characterize phonon bursts with both kinetic inductance detectors and through detecting QP parity switching in charge-sensitive transmons. We will utilize a variety of techniques for the controlled injection of poisoning radiation. For injecting high-energy phonons, we will use tunnel junctions incorporated onto the qubit chips, as well as calibrated À-ray and X-ray sources, both outside and inside the cryostat. We will use Josephson junctions located on separate chips for generating narrow-band mm-wave photons; additionally, we will employ heated thermal sources for generating blackbody photons. For injecting optical photons, we will incorporate a cryogenic laser steering system for pump-probe poisoning experiments. In semiconductors, we will study impacts from the back side of chips, to understand the degree to which defects in SiGe virtual substrates either trap carriers, possibly enhancing noise mechanisms, or serve as a barrier to mitigate the effects of radiation impacts in the bulk of a chip. We will explore several different mitigation strategies for reducing the impact of these different poisoning mechanisms and suppressing correlated errors. Building on our recent initial success with normal metal islands on the substrate back side for promoting phonon downconversion, we will study the dependence of the downconversion efficiency on the thickness and coverage of the metal islands, the electronic mean free path in the metal, and the acoustic impedance mismatch at the metal-substrate interface. We will study various approaches for superconductor gap engineering on the device layer for trapping QPs away from qubit tunnel junctions. In order to scatter high-energy phonons away from qubits, we will develop micromachined structures in the Si substrates and explore the use of alternate substrate materials and orientations. Our project will involve theoretical modeling of the various poisoning mechanisms and mitigation strategies in a close connection with the experimental efforts. The team members for our project at Syracuse University, University of Wisconsin, Madison, SLAC/Stanford, and the J¬ulich Research Center are experts in superconductor and semiconductor qubits and the associated physics of phononic and photonic poisoning mechanisms and QP dynamics. Publicly releasable C
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Oct 12, 2022
- Source ID
- W911NF2210257
Entities
People
- Britton Plourde
Organizations
- Army Contracting Command
- National Security Agency
- Syracuse University