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

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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

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Optical and Quantum Communications Group www.rle.mit.edu/qoptics November 15, 2016

6.453 Quantum Optical Communication Lecture 18 Jeffrey H. Shapiro

www.rle.mit.edu/qoptics 2

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

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www.rle.mit.edu/qoptics 3

Real Photodetection Systems

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“Ideal” Photodetection System: Efficiency < 1

η< 1

PHOTO-

DETECTOR

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www.rle.mit.edu/qoptics 5

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

www.rle.mit.edu/qoptics 6

§ Semiclassical Theory: Given

§ is an inhomogeneous Poisson Counting Process § Rate function

§ Quantum Theory: Semiclassical versus Quantum Photodetection

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www.rle.mit.edu/qoptics 7

Inhomogeneous Poisson Counting Process (IPCP) § Definition: is an IPCP with rate

§ Starts counting at zero: § Has statistically independent increments § Increments are Poisson distributed

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§ Semiclassical Photocount and Photocurrent Mean Functions: § Semiclassical Covariance Functions: Mean and Covariance: Deterministic Illumination

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www.rle.mit.edu/qoptics 9

§ Semiclassical Photocount and Photocurrent Mean Functions: § Semiclassical Covariance Functions: Mean and Covariance: Random Illumination

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Mean and Covariance Functions: Quantum Case § Quantum Photocount and Photocurrent Mean Functions: § Quantum Covariance Functions:

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www.rle.mit.edu/qoptics 11

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:

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Direct-Detection Signatures of Non-Classical Light § Photocurrent Noise Spectral Density for CW Sources: § Semiclassical Theory: § Quantum Theory: § Sub-Shot-Noise Non-Classical Signature:

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www.rle.mit.edu/qoptics 13

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

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

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6.453 Quantum Optical Communication Lecture 18 Jeffrey H. Shapiro

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

Real Photodetection Systems

“Ideal” Photodetection System: Efficiency < 1

η< 1

DETECTOR

3

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

§ Semiclassical Theory: Given

§ is an inhomogeneous Poisson Counting Process § Rate function

§ Quantum Theory: Semiclassical versus Quantum Photodetection

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Inhomogeneous Poisson Counting Process (IPCP) § Definition: is an IPCP with rate

§ Starts counting at zero: § Has statistically independent increments § Increments are Poisson distributed

§ Semiclassical Photocount and Photocurrent Mean Functions: § Semiclassical Covariance Functions: Mean and Covariance: Deterministic Illumination

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§ Semiclassical Photocount and Photocurrent Mean Functions: § Semiclassical Covariance Functions: Mean and Covariance: Random Illumination

Mean and Covariance Functions: Quantum Case § Quantum Photocount and Photocurrent Mean Functions: § Quantum Covariance Functions:

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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:

Direct-Detection Signatures of Non-Classical Light § Photocurrent Noise Spectral Density for CW Sources: § Semiclassical Theory: § Quantum Theory: § Sub-Shot-Noise Non-Classical Signature:

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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

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6.453 Quantum Optical Communication

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