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Weak qubit measurement with a nonlinear cavity: beyond perturbation theory
1Physics Department, McGill University, Montreal, Quebec, Canada.
Physical Review Letters
|September 26, 2012
Summary
We show that increasing coupling strength in nonlinear cavities improves qubit measurement efficiency, approaching the quantum limit. This is due to non-Gaussian photon number fluctuations, offering insights for quantum measurement experiments.
Area of Science:
- Quantum Information Science
- Quantum Optics
- Superconducting Circuits
Background:
- Continuous measurement of qubits is crucial for quantum information processing.
- Nonlinear cavities offer unique properties for quantum measurements.
- Understanding measurement backaction is key to improving qubit control.
Purpose of the Study:
- To analyze the use of a driven nonlinear cavity for continuous qubit measurement.
- To calculate backaction dephasing and measurement rates beyond leading-order perturbation theory.
- To investigate the impact of increasing coupling strength on measurement efficiency.
Main Methods:
- Utilized a driven nonlinear cavity coupled dispersively to a qubit.
- Employed a phase-space approach to calculate rates beyond leading-order perturbation theory.
- Accounted for cavity noise squeezing and non-Gaussian photon number fluctuations.
Main Results:
- Observed that increasing coupling strength beyond linear response improves measurement efficiency.
- Found that efficiency can approach the quantum limit.
- Interpreted this enhancement through nonlinear cavity photon number fluctuations.
Conclusions:
- Nonlinear cavities can significantly enhance qubit measurement efficiency.
- The study provides a theoretical framework for understanding measurement in nonlinear systems.
- Results are relevant for superconducting quantum circuit experiments.
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