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Nonclassical Photon Number Distribution in a Superconducting Cavity under a Squeezed Drive
S Kono1, Y Masuyama1, T Ishikawa1
1Research Center for Advanced Science and Technology (RCAST), The University of Tokyo, Meguro-ku, Tokyo 153-8904, Japan.
Physical Review Letters
|July 29, 2017
Summary
Researchers used a superconducting qubit to detect nonclassical microwave photons. The experiment revealed an even-odd photon number oscillation, confirming the nonclassical nature of light.
Area of Science:
- Quantum optics
- Circuit quantum electrodynamics
- Superconducting quantum circuits
Background:
- Superconducting qubits are sensitive probes of microwave photons.
- The strong dispersive regime reveals photon number information via qubit spectral splitting.
- Nonclassical light states are crucial for quantum information processing.
Purpose of the Study:
- To investigate the photon number distribution of a cavity driven by squeezed vacuum.
- To demonstrate the nonclassical nature of the generated microwave field.
- To utilize a superconducting qubit as a photon-number-resolving detector.
Main Methods:
- Continuous driving of a cavity with squeezed vacuum generated by a Josephson parametric amplifier.
- Measuring the superconducting qubit spectrum in the cavity.
- Fitting the qubit spectrum to a model accounting for finite excitation power.
Main Results:
- The qubit spectrum exhibited peaks corresponding to discrete photon numbers (ac Stark shift).
- The determined photon number distribution showed an even-odd oscillation.
- The results quantitatively satisfied Klyshko's criterion for nonclassicality.
Conclusions:
- The superconducting qubit effectively probed the nonclassical state of microwave photons.
- Even-odd photon number oscillations are a signature of nonclassical states.
- This method provides a robust way to verify nonclassicality in microwave fields.
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