Lecture 18 Jeffrey H. Shapiro Optical and Quantum Communications - PDF document

November 15, 2016 6.453 Quantum Optical Communication Lecture 18 Jeffrey H. Shapiro Optical and Quantum Communications Group www.rle.mit.edu/qoptics 6.453 Quantum Optical Communication - Lecture 18 § Announcements § Pick up random processes notes, lecture notes, slides § Continuous-Time Photodetection § Semiclassical theory — Poisson shot noise § Quantum theory — photon-flux operator measurement § Direct-detection signatures of non-classical light 2 www.rle.mit.edu/qoptics 1

Real Photodetection Systems 3 www.rle.mit.edu/qoptics “ Ideal ” Photodetection System: Efficiency < 1 η < 1 � PHOTO- DETECTOR � 4 www.rle.mit.edu/qoptics 2

Classical Field versus Quantum Field Operator § For Semiclassical Photodetection of Narrowband Light § Illumination is a classical photon-units positive-frequency field: § Short-Time Average Power on Detector: § For Quantum Photodetection of Narrowband Light § Illumination is a photon-units positive-frequency field operator: § Only non-vacuum frequency components are within 5 www.rle.mit.edu/qoptics Semiclassical versus Quantum Photodetection § Semiclassical Theory: Given § is an inhomogeneous Poisson Counting Process § Rate function § Quantum Theory: 6 www.rle.mit.edu/qoptics 3

Inhomogeneous Poisson Counting Process (IPCP) § Definition: is an IPCP with rate § Starts counting at zero: § Has statistically independent increments § Increments are Poisson distributed 7 www.rle.mit.edu/qoptics Mean and Covariance: Deterministic Illumination § Semiclassical Photocount and Photocurrent Mean Functions: § Semiclassical Covariance Functions: 8 www.rle.mit.edu/qoptics 4

Mean and Covariance: Random Illumination § Semiclassical Photocount and Photocurrent Mean Functions: § Semiclassical Covariance Functions: 9 www.rle.mit.edu/qoptics Mean and Covariance Functions: Quantum Case § Quantum Photocount and Photocurrent Mean Functions: § Quantum Covariance Functions: 10 www.rle.mit.edu/qoptics 5

Direct-Detection Signatures of Non-Classical Light § Semiclassical Theory is Quantitatively Correct: § For coherent-state inputs § For inputs that are classically-random mixtures of coherent states § Sub-Poissonian Photon Counting: § Semiclassical theory: § Quantum theory: § Non-classical signature: 11 www.rle.mit.edu/qoptics Direct-Detection Signatures of Non-Classical Light § Photocurrent Noise Spectral Density for CW Sources: § Semiclassical Theory: § Quantum Theory: § Sub-Shot-Noise Non-Classical Signature: 12 www.rle.mit.edu/qoptics 6

Coming Attractions: Lecture 19 § Lecture 19: 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 13 www.rle.mit.edu/qoptics 7

MIT OpenCourseWare https://ocw.mit.edu 6.453 Quantum Optical Communication Fall 2016 For information about citing these materials or our Terms of Use, visit: https://ocw.mit.edu/terms.