22
December
2023
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07:57 AM
America/New_York

Scientists Focus on Understanding Source of Noise--A Major Issue in Quantum Computing

Washington, D.C.–December 22, 2023. In a recent paper published in Physical Review Letters,  Universities Space Research Association's Filip Wudarski and his team showed that understanding the source of noise is of primary importance for quantum computers.

Graph displaying outcome distributions of different number of measurement observations (different colors). In the nonergodic limit (when the number of measurements is slow) the distribution displays a fine structure that is characteristic to coupling with two-level-systems. When the number of measurements is sufficiently long (the ergodic limit, orange curve), the distribution takes smooth pseudo-binomial shape.

Outcome distributions of different number of measurement observations (different colors). In the nonergodic limit (when the number of measurements is slow) the distribution displays a fine structure that is characteristic to coupling with two-level-systems. When the number of measurements is sufficiently long (the ergodic limit, orange curve), the distribution takes smooth pseudo-binomial shape.

The paper discusses how scientists can study the specific features of low-frequency noise in a quantum bit (qubit) using relatively short measurements. These measurements are shorter than the time it takes for the noise source to explore all its possible states, and thus reach the ergodic limit.

Nonergodic measurements provide a snapshot of the noise source's distribution across its states with the information usually averaged out in long measurements. Therefore, nonergodic measurements are sensitive to both the origin of the noise and the parameters of the noise source. This sensitivity is especially noticeable when dealing with noise from two-level systems, which are considered a significant cause of low-frequency noise in qubits.

The paper also reveals that the transition to a quasi-ergodic limit (a state where the system behaves similarly to an ergodic system) can happen before the noise source explores all its states. This transition can strongly depend on how the measurements are conducted.

Additional Resources: (https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.131.230201).

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Founded in 1969, under the auspices of the National Academy of Sciences at the request of the U.S. Government, the Universities Space Research Association (USRA) is a nonprofit corporation chartered to advance space-related science, technology, and engineering. USRA operates scientific institutes and facilities and conducts other major research and educational programs. USRA engages the university community and employs in-house scientific leadership, innovative research and development, and project management expertise. More information about USRA is available at www.usra.edu.