MIT OpenCourseWarehttp://ocw.mit.edu 6.453 Quantum Optical Communication Spring 2009 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms.November 20, 2008Optical and Quantum Communications Groupwww.rle.mit.edu/qoptics6.453 Quantum Optical CommunicationLecture 19Jeffrey H. Shapiro2www.rle.mit.edu/qoptics6.453 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 light3www.rle.mit.edu/qopticsSemiclassical versus Quantum Photodetection! Semiclassical Theory: Given! is an inhomogeneous Poisson Impulse Train! Rate function! Quantum Theory:4www.rle.mit.edu/qopticsStationary Statistics for Continuous-Wave Sources! Stationary Mean and Covariance Functions:! Semiclassical Photodetection:! Quantum Photodetection:5www.rle.mit.edu/qopticsPhotocurrent Noise Spectral Density! Photocurrent Noise Spectral Density:! Propagation Through a Linear Time-Invariant Filter:! Physical Interpretation: = mean-squared fluctuationstrength per unit bilateral bandwidth (in Hz) in frequencycomponents of6www.rle.mit.edu/qopticsDirect-Detection Signatures of Non-Classical Light! Semiclassical Theory:! Quantum Theory:! Sub-Shot-Noise Non-Classical Signature:7www.rle.mit.edu/qopticsBalanced Homodyne Detection! Signal = , LO =! Low-Pass Filter:LPF8www.rle.mit.edu/qopticsBalanced 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:9www.rle.mit.edu/qopticsBalanced Heterodyne Detection! Signal =! LO =! Band-Pass Filter:BPF10www.rle.mit.edu/qopticsBalanced 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:11www.rle.mit.edu/qopticsCoherent-Detection Non-Classical Light Signatures! Semiclassical Theory (within filter passband):! Quantum Theory (within filter passband):! Sub-Shot-Noise Spectra are Non-Classical:12www.rle.mit.edu/qopticsComing 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
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