Lecture 19 Jeffrey H. Shapiro Optical and Quantum Communications - - PDF document

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Optical and Quantum Communications Group www.rle.mit.edu/qoptics November 17, 2016

6.453 Quantum Optical Communication Lecture 19 Jeffrey H. Shapiro

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6.453 Quantum Optical Communication - Lecture 19 § Announcements

§ Pick up lecture notes, slides

§ Continuous-Time Photodetection

§ Noise spectral densities in direct detection § Semiclassical theory of coherent detection § Quantum theory of coherent detection § Coherent-detection signatures of non-classical light

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Semiclassical versus Quantum Photodetection § Semiclassical Theory: Given

§ is an inhomogeneous Poisson Impulse Train § Rate function

§ Quantum Theory:

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Stationary Statistics for Continuous-Wave Sources § Stationary Mean and Covariance Functions: § Semiclassical Photodetection: § Quantum Photodetection:

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Photocurrent Noise Spectral Density § Photocurrent Noise Spectral Density: § Propagation Through a Linear Time-Invariant Filter: § Physical Interpretation: = mean-squared fluctuation strength per unit bilateral bandwidth (in Hz) in frequency components of

ω

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Direct-Detection Signatures of Non-Classical Light § Semiclassical Theory: § Quantum Theory: § Sub-Shot-Noise Non-Classical Signature:

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Balanced Homodyne Detection § Signal = , LO = § Low-Pass Filter: LPF

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Balanced Homodyne Detection (Within Passband) § Semiclassical Statistics in Strong Local Oscillator Limit:

§ Gaussian-process local oscillator shot noise:

§ Quantum Statistics in Strong Local Oscillator Limit:

§ Gaussian-process sub-unity quantum efficiency noise:

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Balanced Heterodyne Detection § Signal = § LO = § Bandpass Filter: BPF

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Balanced Heterodyne Detection (Within Passband) § Semiclassical Statistics in Strong Local Oscillator Limit:

§ Gaussian-process local oscillator shot noise:

§ Quantum Statistics in Strong Local Oscillator Limit:

§ Gaussian-process sub-unity quantum efficiency noise:

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Coherent-Detection Non-Classical Light Signatures § Semiclassical Theory (within filter passband): § Quantum Theory (within filter passband): § Sub-Shot-Noise Spectra (in passband) are Non-Classical:

Sihomihom(ω) ≥ Siηiη(ω) = q2η(1 − η)PLO ~ω0

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Coming Attractions: Lecture 20 § Lecture 20: Nonlinear Optics of Interactions

§ Maxwell’s equations with a nonlinear polarization § Coupled-mode equations for parametric downconversion § Phase-matching for efficient interactions

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6.453 Quantum Optical Communication

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