Continuous quantum measurement with independent detector cross correlations.

Area of Science:

• Quantum Information Science
• Quantum Optics
• Condensed Matter Physics

Background:

• Continuous quantum measurement is crucial for monitoring quantum systems.
• Detector performance, especially in single-shot and weak measurement regimes, is a key challenge.
• Understanding correlations between detectors is vital for advancing measurement precision.

Purpose of the Study:

• To explore the benefits of employing two independent linear detectors for continuous quantum measurement.
• To analyze the impact of detector correlations on measurement limitations and signal-to-noise ratios.
• To investigate the joint weak measurement of noncommuting observables and its frequency dependence.

Main Methods:

• Theoretical analysis of continuous quantum measurement using two independent linear detectors.
• Investigation of single-shot measurement scenarios with identical ('twin') detectors.
• Analysis of cross-correlations in weak continuous measurements to assess signal-to-noise ratios.
• Study of joint weak measurements of noncommuting observables, examining frequency-dependent cross-correlations.

Main Results:

• Identical detectors can lead to quantum-limited performance in single-shot measurements.
• Cross-correlations between detectors enable violation of the Korotkov-Averin bound for signal-to-noise ratio in weak measurements.
• The cross-correlation sign changes with frequency, indicating a transition from incoherent relaxation to coherent oscillations.
• Application of these principles to a double quantum-dot charge qubit measured by quantum point contacts.

Conclusions:

• Two independent linear detectors offer significant advantages for continuous quantum measurement.
• Detector cross-correlations provide a powerful tool to enhance measurement precision and probe quantum dynamics.
• The findings are directly relevant to experimental implementations using quantum dot systems.