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A Photonic System for Generating Unconditional Polarization-Entangled Photons Based on Multiple Quantum Interference
Published on: September 5, 2019
Nonclassical photon pair production in a voltage-biased Josephson junction
Juha Leppäkangas1, Göran Johansson, Michael Marthaler
1Microtechnology and Nanoscience, MC2, Chalmers University of Technology, SE-412 96 Göteborg, Sweden.
Physical Review Letters
|July 16, 2013
Summary
Quantum fluctuations in superconducting transmission lines generate photon pairs from Josephson junctions. This nonclassical behavior, observed below the Josephson frequency, violates classical inequalities and can be enhanced using stepped transmission lines.
Area of Science:
- Quantum optics
- Condensed matter physics
- Superconductivity
Background:
- Josephson junctions are key quantum devices exhibiting unique electromagnetic properties.
- Quantum fluctuations in superconducting circuits can lead to observable phenomena.
Purpose of the Study:
- To investigate electromagnetic radiation emitted by voltage-biased Josephson junctions coupled to superconducting transmission lines.
- To explore the role of quantum fluctuations in generating radiation below the Josephson frequency.
- To provide evidence for nonclassical photon pair production.
Main Methods:
- Theoretical analysis using an input-output formalism for microwave fields.
- Calculation of photon-flux spectra and Cauchy-Schwarz inequality for two-mode correlations.
- Consideration of stepped transmission lines to enhance signal-to-noise ratio.
Main Results:
- Observed extra radiation below the Josephson frequency, driven by quantum fluctuations.
- Identified symmetric photon-flux spectra around half the Josephson frequency, indicating photon pair creation.
- Demonstrated violation of the classical Cauchy-Schwarz inequality, confirming nonclassical photon pair production.
- Showed that resonances in stepped transmission lines improve signal-to-noise ratio.
Conclusions:
- Quantum fluctuations in transmission lines are crucial for generating nonclassical photon pairs from Josephson junctions.
- The observed phenomena highlight the quantum nature of electromagnetic radiation in superconducting circuits.
- Stepped transmission lines offer a promising avenue for enhancing experimental detection of these quantum effects.
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