Scientists from the I.B.M Watson Research Center in the USA have presented research into the dynamics of superconducting qubit relaxation times, a key candidate for high-performance quantum computing. Their findings have appeared online in the journal npj Quantum Information.
Study: Dynamics of superconducting qubit relaxation times. Image Credit: Production Perig/Shutterstock.com
Quantum computing harnesses quantum mechanics phenomena, such as entanglement, interference, and superposition to solve advanced computational problems that conventional computers cannot address. Types of quantum computer models include quantum circuits, quantum annealing, Turing machines, and adiabatic quantum computation.
At the core of quantum computing techniques is the qubit, which is short for a quantum bit. This is analogous to classical “bits” used in conventional computing systems. Technically, any mathematical problem that can be solved using a quantum computer can also be solved using a conventional computer, but it would take much longer to find a solution.
Currently, quantum computing faces several key challenges, such as maintaining the qubit’s quantum states due to quantum decoherence. Therefore, currently, error correction is needed to resolve problems.
To overcome current issues with quantum computing, recent studies have proposed what are known as superconducting qubits. The development of these types of qubits has caused a five-fold order of magnitude coherence time improvement since coherent dynamics were first realized.
Further improvements are necessary to fully realize the potential of superconducting qubits to enhance the performance of quantum processors. Additionally, constructing quantum computers with optimal fault tolerance remains a key challenge in the field of quantum computing.
Recent key advances have been made in the realization of two-qubit systems with enhanced gate control. These advances have made it possible to impart quantum systems with gate fidelities that exceed fault tolerance thresholds by significantly enhancing their coherence. Research has produced systems that possess fidelities near their coherence limits.
An important theme in research is the impact on the performance of multi-qubit devices by the system’s coherence stability. This is in large part due to temporal fluctuations that superconducting qubits display. Currently, there is much focus on benchmarking device coherence and providing strategies that mitigate crucial errors which would otherwise cause issues in systems.
Two-level systems have emerged as suitable candidates in recent research because of their effects on superconducting qubit-based circuit coherence properties. These effects have been attributed to amorphous material defects. Temporal fluctuations in the frequency environment can partially explain energy relaxation time variability. A key factor in this variation is the two-level system’s spectral diffusion.
The new paper in the journal npj Quantum Information has demonstrated a novel fast spectroscopy technique for investigating these systems. The proposed technique utilizes a microwave-based approach, and a major advantage is that it requires no extra hardware.
Microwave tones that possess off-tone characteristics are utilized in the author’s approach, which provides enhanced spectral resolution of relaxation times. This significantly improves on conventional flux-based two-level system spectroscopy methods. Frequency levels are revealed by relaxation time dips, and repetitive frequency sweeps are used to investigate the system’s relaxation probability time dynamics.
Long and short-time means were correlated by the authors using this approach, both over the span of multiple months and local qubit frequencies, which were used to average short-time means across ten qubits.
Correlation strength suggested that the system displays behaviors that are quasi-ergodic in nature. Conversely, the authors observed a reduced correlation between measurements over the course of one day. It was concluded that local qubit frequency provides an enhanced and rapid correlation of long-term behavior.
Quantum computers are arguably the future of computing, offering outstanding performance and resolution of advanced mathematical problems far in excess of their conventional counterparts. However, some key challenges persist, which hinder the widespread implementation of quantum computers.
Superconducting qubits have emerged as candidates for future advanced quantum computers mainly because of their enhanced coherence. To analyze these systems, however, requires robust and reliable spectroscopy approaches.
The study’s approach, utilizing an all-microwave technique, can provide significant improvements to the field of quantum computing, revealing the dynamics and correlations in advanced superconducting qubit-based systems. Whilst bottlenecks remain, this is a step toward fully-realized fault-free quantum computing technologies.
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Carroll, M et al. (2022) Dynamics of superconducting qubit relaxation times npj Quantum Information 8 article no.: 132 [online] nature.com. Available at:
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