Superconducting Quantum Processors Face Radiation Threat to Stability

As scientists push the boundaries of quantum computing, a critical challenge has emerged: the impact of high-energy particles from background radioactivity or cosmic-ray muons on superconducting quantum processors. These particles can generate energetic phonons that travel throughout the substrate, leading to widespread quasiparticle formation and affecting qubit stability. Researchers have developed numerical models to simulate these dynamics, revealing the importance of considering phonon-mediated quasiparticle poisoning in device design and operation. To mitigate this threat, scientists are exploring strategies such as radiation-hardened materials, optimized geometries, and advanced error correction techniques – essential steps toward realizing fault-tolerant quantum computers.

Can Superconducting Quantum Processors Survive Ionizing Radiation?

The operation of superconducting quantum processors is plagued by a significant challenge: ionizing radiation. High-energy particles from background radioactivity or cosmic-ray muons impacting superconducting qubit arrays can cause correlated errors, making it difficult to implement a fault-tolerant quantum processor. A typical gamma ray from background radioactive contamination hitting the qubit chip deposits energy of order 100 keV in the Si substrate, generating a significant number of electron-hole pairs near the impact site.

These electron-hole pairs can recombine or travel distances of a few hundred µm before trapping on defects in the Si, causing a reconfiguration of the offset-charge environment for any qubits near the impact site. This can lead to rearrangements of the local two-level system defects near a qubit, shifting its frequency and affecting its coherence. Moreover, the generation of these electron-hole pairs is accompanied by the emission of many energetic athermal phonons that travel throughout the entire volume of the substrate.

These phonons generally have energies well above the superconducting energy gap on the device layer when emitted, which can lead to quasiparticle excitations in the qubit electrodes. This temporary reduction in qubit coherence is significant and can cause errors on a large fraction of the qubits in an array simultaneously. The many energetic phonons produced by a particle impact travel efficiently throughout the device substrate and generate quasiparticles with high probability, thus causing errors on a large fraction of the qubits in an array simultaneously.

What are Quasiparticle Excitations and How Do They Affect Qubit Coherence?

Quasiparticle excitations refer to the temporary reduction in qubit coherence caused by the emission of energetic phonons. These phonons can travel throughout the device substrate, generating quasiparticles with high probability. The many energetic phonons produced by a particle impact can lead to significant errors on a large fraction of the qubits in an array simultaneously.

The generation of these electron-hole pairs is accompanied by the emission of many energetic athermal phonons that travel throughout the entire volume of the substrate. These phonons generally have energies well above the superconducting energy gap on the device layer when emitted, which can lead to quasiparticle excitations in the qubit electrodes. This temporary reduction in qubit coherence is significant and can cause errors on a large fraction of the qubits in an array simultaneously.

The many energetic phonons produced by a particle impact travel efficiently throughout the device substrate and generate quasiparticles with high probability, thus causing errors on a large fraction of the qubits in an array simultaneously. This phenomenon is known as phonon-mediated quasiparticle poisoning, which can have significant implications for the operation of superconducting quantum processors.

How Do Researchers Model Phonon-Mediated Quasiparticle Poisoning?

Researchers have developed a comprehensive strategy for the numerical simulation of phonon and quasiparticle dynamics in the aftermath of an impact. This approach involves comparing simulations with experimental measurements of phonon-mediated QP poisoning, demonstrating that modeling captures the spatial and temporal footprint of the QP poisoning for various configurations of phonon downconversion structures.

The researchers used a combination of theoretical models and numerical simulations to study the behavior of phonons and quasiparticles in superconducting qubit arrays. They found that the many energetic phonons produced by a particle impact travel efficiently throughout the device substrate, generating quasiparticles with high probability. This phenomenon is known as phonon-mediated quasiparticle poisoning.

The researchers’ modeling strategy involves simulating the behavior of phonons and quasiparticles in superconducting qubit arrays, taking into account various configurations of phonon downconversion structures. They compared their simulations with experimental measurements of phonon-mediated QP poisoning, demonstrating that modeling captures the spatial and temporal footprint of the QP poisoning.

What are the Implications of Phonon-Mediated Quasiparticle Poisoning for Superconducting Quantum Processors?

The phenomenon of phonon-mediated quasiparticle poisoning has significant implications for the operation of superconducting quantum processors. The many energetic phonons produced by a particle impact can lead to temporary reductions in qubit coherence, causing errors on a large fraction of the qubits in an array simultaneously.

This phenomenon is known as phonon-mediated quasiparticle poisoning, which can have significant implications for the operation of superconducting quantum processors. The researchers’ modeling strategy involves simulating the behavior of phonons and quasiparticles in superconducting qubit arrays, taking into account various configurations of phonon downconversion structures.

The implications of phonon-mediated quasiparticle poisoning are far-reaching, with significant consequences for the operation of superconducting quantum processors. The researchers’ modeling strategy provides a valuable tool for understanding this phenomenon and developing strategies to mitigate its effects.

Can Superconducting Quantum Processors Be Made Fault-Tolerant?

The challenge of implementing a fault-tolerant quantum processor is significant, given the impact of ionizing radiation on superconducting qubit arrays. However, researchers are exploring various strategies to mitigate this effect and make superconducting quantum processors more robust.

One approach involves developing materials with improved radiation resistance, which can help reduce the impact of ionizing radiation on superconducting qubit arrays. Another strategy involves designing qubit architectures that are less susceptible to errors caused by phonon-mediated quasiparticle poisoning.

Researchers are also exploring new materials and technologies that can help mitigate the effects of phonon-mediated quasiparticle poisoning. These include advanced materials with improved radiation resistance, as well as novel qubit architectures that are designed to be more robust against errors caused by this phenomenon.

While significant challenges remain, researchers are making progress in developing strategies to make superconducting quantum processors more fault-tolerant. The development of new materials and technologies holds promise for improving the reliability and performance of these devices.