Material Assays Project Radiation Rates for SNOLAB Qubit Measurements

Shielded by two kilometers of rock, the Cryogenic Underground TEst (CUTE) facility at SNOLAB is designed to provide an ultra-low radiation environment for probing quantum coherence in superconducting qubits. A team of researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo, including Y. Ahmed, B. Binoy, and R. Bunker, has completed an extensive material assaying program in preparation for operating superconducting qubits underground, meticulously characterizing potential sources of interference. The work reports on a thorough Monte Carlo study utilizing the Geant4 particle physics tracking code to project radiation exposure for these sensitive quantum devices. Researchers further characterized the spectral components of the projected background and identify the dominant particle interaction types, moving beyond simply measuring total radiation to pinpoint the specific challenges for qubit performance.

Researchers are not simply measuring total radiation; they are meticulously characterizing the specific sources impacting qubit performance. An extensive material assaying program was undertaken in preparation for the first underground operation of superconducting qubits, forming the basis of a detailed radiation exposure projection. This work leverages the power of the Geant4 particle physics tracking code, a sophisticated simulation tool used to model the interactions of radiation with the experimental setup. The project, spearheaded by researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo, aims to compare qubit coherence times measured on the surface to those measured deep underground, providing a controlled environment to isolate radiation’s effects. Understanding these effects is paramount, as even a single high-energy interaction can create cascades of excitations affecting multiple qubits, violating assumptions critical to quantum error correction. The research extends to crystal dynamics simulations using the G4CMP solid-state physics extension for Geant4, informing strategies to mitigate the impact of high-energy particle interactions and ultimately improve qubit resilience.

The pursuit of stable quantum coherence in superconducting qubits faces a persistent challenge: ionizing radiation. Recent work details an extensive effort to quantify and mitigate this threat, particularly for experiments conducted deep underground at SNOLAB. Researchers initiated a comprehensive material assaying program to precisely characterize the radioactivity present in components destined for CUTE, feeding these data into a sophisticated radiation exposure projection. The simulations allowed the team to estimate energy deposits from radiogenic sources expected for a quantum-device assembly. The team’s goal is to compare results of coherence times measured in surface laboratories to those deep underground at SNOLAB.

Shielded by an impressive 2 kilometers of rock overburden, CUTE offers a uniquely ultra-low radiation environment intended to isolate and study quantum coherence, a critical factor in qubit performance. This substantial depth is equivalent to 6000 meters of water coverage, creating conditions ideal for sensitive quantum experiments. This detailed analysis, combining material assays with sophisticated modeling, aims to provide a comprehensive understanding of the background radiation and its influence on the fragile quantum states of superconducting qubits, ultimately advancing the field of quantum error correction.

The pursuit of stable qubits often overlooks a critical design constraint: minimizing interaction with the very environment intended to isolate them. While superconducting transmon qubits represent a leading architecture for quantum computing, their sensitivity to ionizing radiation demands increasingly sophisticated mitigation strategies. These qubits, designed as anharmonic LC oscillators with Josephson junctions embedded in planar microwave circuitry, rely on maintaining fragile quantum states long enough to perform calculations. Improving coherence time, a key metric for qubit performance, has been a central focus, yet experimental studies have repeatedly demonstrated that even trace amounts of radiation can induce decoherence. Researchers have observed time-correlated quantum errors extending across entire device substrates, stemming from non-equilibrium quasiparticles generated by ionizing radiation. A single high-energy event can cascade, affecting multiple qubits and undermining the assumptions of most quantum error correction schemes.

The fragility of quantum states demands unprecedented control over environmental disturbances, and recent research highlights the insidious impact of ionizing radiation on superconducting qubits. Experimental studies have demonstrated that exposure to this radiation can induce decoherence, the loss of quantum information, in qubits, resonators, and SQUIDs, disrupting the delicate quantum processes necessary for computation. Critically, researchers have observed “sequences of quantum errors correlated in time” extending across entire device substrates, suggesting a systemic vulnerability. These correlated errors, stemming from the generation of non-equilibrium quasiparticles, pose a significant challenge to established quantum error correction schemes reliant on sparse, uncorrelated errors. To address this, researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo collaborated to investigate radiation’s effects on quantum technologies, focusing on coherence studies.

The pursuit of stable qubits faces a subtle but significant threat: not merely the presence of radiation, but the way it manifests as correlated errors. Shielded by 2 kilometers of rock overburden, equivalent to 6000 meters of water coverage, the CUTE facility at SNOLAB provides a unique ultra-low radiation environment to probe the performance of quantum technologies. The simulations model the remaining background and its impact on qubit coherence, informing efforts to engineer more resilient qubit designs and effective error correction schemes.

Researchers within the QUTEbits collaboration are meticulously characterizing potential radiation sources for upcoming superconducting qubit experiments housed deep underground at SNOLAB. Consisting of researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo, the University of Toronto, and Chalmers University of Technology, the project aims to understand how ionizing radiation impacts quantum coherence and error rates. A central component of their approach is a detailed analysis of materials used in the experiment itself, coupled with sophisticated modeling. The simulations enable researchers to estimate “the rates of energy deposits from radiogenic sources” expected within CUTE. Shielded by 2 kilometers of rock overburden, CUTE offers an ultra-low radiation environment, but precise modeling is still essential to interpret experimental results and refine qubit designs for resilience.

The quest for stable qubits faces a relentless adversary: ionizing radiation. Originally constructed for the SuperCDMS SNOLAB dark matter experiment, CUTE has been repurposed as a platform for probing quantum coherence, shielded by an extraordinary 2 kilometers of rock overburden equivalent to 6000 meters of water coverage. An “extensive material assaying program” underpinned the project, meticulously quantifying the radioactivity present in materials destined for the underground experiment. This detailed approach, combining material analysis with sophisticated simulation, represents a significant step towards understanding and overcoming the challenges posed by radiation in the pursuit of robust quantum computing.