DEMETRA: Suppression of the Relaxation Induced by Radioactivity in Superconducting Qubits

Abstract

Non-equilibrium quasiparticles can deteriorate the performance of superconducting qubits by reducing their coherence. We are investigating a source of quasiparticles that has been too long neglected, namely radioactivity: cosmic rays, environmental radioactivity and contaminants in the materials can all generate phonons of energy sufficient to break Cooper pairs and thus increase the number of quasiparticles. In this contribution, we describe the status of the project and its perspectives.

Sensor-assisted fault mitigation in quantum computation

“…Recent reports [1][2][3] show deleterious effects in superconducting kinetic inductance devices and superconducting transmon qubits correlated with ionizing radiation levels, identifying yet another mechanism causing decoherence. As others have [4], we postulate these observed phenomena stem from the same underlying process: the instantaneous injection of energy into the superconducting device and the device's substrate as a result of impinging ionizing radiation. It is possible to reduce the rate of ionizing radiation energy injections by shielding against naturally occurring radiation sources in the laboratory and by placing systems underground to shield against cosmic rays.…”

“…10(a) & (e) ), suggesting error inducing effects beyond simple Poisson statistical variation. 4 The noise model for the Yorktown backend (Fig. 10(b) & (f) ), however, shows Poissonian statistical variation, as expected for a fixed, deterministic simulation process.…”

Extending superconducting qubit lifetimes: What’s Next?

“…As a final side note, it is interesting to see that qubit coherence times have gotten long enough that in the near future, cosmic rays and radioactive decay events may become a limiting factor that will require amelioration [22]. A number of recent experiments in MKIDs (bolometers based on kinetic inductance changes) [23,24] and in superconducting qubits and qubit arrays [25][26][27] have seen convincing evidence for cosmic ray energy deposition causing burst events in which one or multiple qubits temporarily fail due to an excess of broken Cooper pairs created by the energy deposition. Correlated errors, which are especially are dangerous for quantum error correction, come about across large distances because it is hard for the superconducting quasiparticles to thermalize and fall back into the superconducting condensate.…”

Strain-spectroscopy of strongly interacting defects in superconducting qubits

“…To date, such a coupled system constitutes the building block for the state-of-the-art prototypes of solid-state-based quantum processors [2]. Unfortunately, it is still challenging to preserve the qubits' coherence for a long time due to the unavoidable interaction with their environment [3,4], including cosmic rays [5,6]. A dominant source of decoherence is the random formation of natural defects at circuit interfaces and inside the Josephson junctions (JJs), whereby a qubit is highly sensitive [7][8][9][10].…”