Superconducting qubits, the building blocks of quantum computers, are not immune to noise, including qubit decoherence and imperfect operations, which limit their computational abilities. A study on an IBM Quantum system investigated the error dynamics of these qubits, specifically focusing on measurement-induced state transitions (MIST). The research found that the qubit error rate changes abruptly during specific time intervals due to resonant transition between fluctuating dressed states of the qubits. These findings are crucial for improving quantum computer performance and highlight the need for further research into MIST dynamics and error mitigation techniques.
What are Superconducting Qubits, and Why Are They Important?
Superconducting qubits are artificial atoms that serve as the fundamental building blocks of quantum computers. Quantum computers, which leverage the principles of quantum mechanics, are expected to exceed the computational abilities of classical computers far. Superconducting qubits have gained significant attention due to their relatively long coherence times and the ability to implement fast gate operations. They are well described by the Jaynes-Cummings model, a mathematical model that describes the interaction between light and matter.
However, existing superconducting quantum computers are not immune to noise, including qubit decoherence and imperfect qubit operations. These factors ultimately limit the computational abilities and degrade the fidelity of qubit outputs. Several surveys have revealed that qubit errors fluctuate over time, which presents a significant challenge for current error mitigation techniques. Therefore, it is crucial to investigate the error dynamics of superconducting qubit systems.
What is the Measurement-Induced State Transition (MIST) in Superconducting Qubits?
Previous reports have extensively studied the mechanism of measurement-induced state transitions (MIST). MIST occurs when the measurement stimulus is injected into the readout cavity, causing qubit-dressed states to come into resonance and the qubit to be excited beyond the computational subspace. It was reported that the resonance shows a noisy behavior when measured repeatedly, which can be attributed to a fluctuating offset charge. However, the early studies are limited to a system of superconducting qubits coupled with low-frequency readout resonators. In addition, the dynamics of MIST has not been fully investigated.
How was the Study Conducted?
This study conducted a time-resolved MIST experiment for qubits in an IBM Quantum system coupled with high-frequency readout resonators. The experiment was performed for a total duration of approximately 2.7 x 10^5 seconds, and the occurrence rate and the duration of MIST were analyzed. The researchers probed how dressed state energy fluctuates over time and temporarily resonates with other energy levels.
The experiments were performed on ibm-kawasaki, an IBM Quantum system. This processor had 27 transmon qubits, and qubit 7 in this processor was used. The qubit frequency is ω01/2π = 5.457 GHz with the anharmonicity η/2π=336.6 MHz and the energy relaxation time is 104.9µs. The qubit is capacitively coupled to a readout resonator with its fundamental frequency ωr/2π = 7.117 GHz and the decay rate κ = 1/209 ns. The coupling strength between the qubit and the resonator is g/2π = 868.5 MHz. The readout assignment error for this qubit is 1.46%.
What are the Findings of the Study?
The researchers found that the qubit error rate abruptly changes during specific time intervals. Each high error state persists for several tens of seconds and exhibits an on-off behavior. The observed temporal instability can be attributed to qubit transitions induced by a measurement stimulus. The resonant transition between fluctuating dressed states of the qubits and high-frequency resonators can be responsible for the error-rate change.
What are the Implications of the Study?
The findings of this study are significant as they provide insights into the dynamics of measurement-induced state transitions in superconducting qubits. Understanding these dynamics is crucial for improving the performance of quantum computers. The study also highlights the need for further research to fully understand the dynamics of MIST and develop effective error mitigation techniques.
“Dynamics of measurement-induced state transitions in superconducting
qubits”, was published in arXiv (Cornell University) on 2024-02-08; the authors are Yuta Hirasaki, Shunsuke Daimon, Naoki Kanazawa, Toshinari Itoko, Masao Tokunari, and Eiji Saitoh. Find more at https://doi.org/10.48550/arxiv.2402.05409
