Multi-Level Noise Spectroscopy for Quantum Systems
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Solution Overview
Problem
Existing quantum noise spectroscopy protocols are limited in their ability to distinguish between underlying noise processes in quantum systems, particularly when applied to multi-level systems like weakly anharmonic qubits, which are crucial for scalable quantum information processors.
Innovation Solution
A spin-locking-based quantum noise spectroscopy protocol that utilizes the multi-level energy structure of superconducting qubits to identify and distinguish contributions from various noise sources by probing higher-excited states, expanding the spectral range and enabling the identification of different noise mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing quantum noise spectroscopy protocols are used, then noise spectral content can be extracted, but the ability to distinguish between underlying noise processes is limited
Solution Approach 1:
The patent segments the quantum system into multiple energy levels (ground state, first excited state, second excited state) and uses transitions between different level pairs (|0⟩-|1⟩ and |1⟩-|2⟩) to probe different aspects of the noise spectrum. This segmentation allows the system to extract both the power spectral density and the cross-spectral density between different noise sources, thereby distinguishing between underlying noise processes while maintaining accurate spectral content extraction.
2Device complexity
If two-level system approximation is used, then QNS protocols are simpler to implement, but bandwidth is limited when applied to weakly anharmonic qubits
Solution Approach 1:
The patent transitions from the traditional two-level system approximation to a multi-level system approach by incorporating the second excited state |2⟩. This dimensional expansion allows the system to access higher frequency components of the noise spectrum through the |1⟩-|2⟩ transition, thereby increasing the effective bandwidth for noise spectroscopy on weakly anharmonic qubits while maintaining a manageable increase in experimental complexity.
3Loss of information
If multi-level structure is utilized, then noise contributions from various sources can be distinguished, but the quantum system complexity increases
Solution Approach 1:
The patent employs a feedback mechanism where the measured quantities (populations of energy levels and transition rates) are used to reconstruct the noise spectrum through an inverse problem formulation. By measuring the steady-state populations and transition rates between different levels, and then using these measurements to infer the underlying noise spectral density, the system achieves noise source discrimination without requiring direct observation of the noise sources themselves, thereby managing the increased system complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for the extraction of noise contributions from multiple sources, improving the coherence and performance of quantum systems by providing detailed noise spectra information, which can be used to enhance hardware design and reduce noise-related limitations.
Implementation Method 1
measuring values of one or more observables of the quantum system that quantify the quantum system's response to the noise sources and the one or more applied control signals
Implementation Method 2
extracting noise spectra information associated with the noise sources from the measured values
Data Source
AI summary
According to some embodiments, a method can identify and discriminate contributions from one or more noise sources using the multi-level structure of a quantum system with three or more levels. The method can include: preparing the quantum system in a predetermined state; applying one or more control signals to the quantum system; measuring values of one or more observables of the quantum system that quantify the quantum system's response to the noise sources and the one or more applied control signals; extracting noise spectra information associated with the noise sources from the measured values; and identifying contributions from the one or more noise sources based on the noise spectra information.