Lecture 10 Jeffrey H. Shapiro Optical and Quantum Communications - - PDF document

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Optical and Quantum Communications Group www.rle.mit.edu/qoptics October 13, 2016

6.453 Quantum Optical Communication Lecture 10 Jeffrey H. Shapiro

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6.453 Quantum Optical Communication - Lecture 10 § Announcements

§ Turn in problem set 5 § Pick up problem set 5 solutions, problem set 6, lecture notes, slides

§ Single-Mode Photodetection

§ Signatures of non-classical light § Squeezed-state waveguide tap

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Single-Mode Semiclassical Photodetection § Photon-Units Classical Field: § Direct Detection: given , is Poisson with mean § Homodyne Detection: given , § Heterodyne Detection: given ,

a a a

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Single-Mode Quantum Photodetection § Photon-Units Field Operator:

for

§ Direct Detection: measurement § Homodyne Detection: measurement § Heterodyne Detection: measurement

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Single-Mode Random Fields: Classical vs. Quantum § Classical Field: complex random variable

§ Measurement variances

§ Quantum Field: density operator of the excited mode

§ Measurement variances where

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Signatures of Non-Classical Light § “Classical Light” = random mixture of coherent states § Sub-Poissonian Statistics: § Quadrature-Noise Squeezing: § Heterodyne-Detection Statistics Determine

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Optical Waveguide Tap — Semiclassical

§ Coupler is a beam splitter § Tap input is zero § Homodyne SNR at signal input § Homodyne SNR at signal output § Homodyne SNR at tap output Fused Fiber Coupler

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Optical Waveguide Tap — Quantum

§ Coupler is a beam splitter Fused Fiber Coupler § Tap input is in squeezed vacuum § Homodyne SNR at signal input § Homodyne SNR at signal output § Homodyne SNR at tap output

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Optical Waveguide Tap: SNR Tradeoff

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Non-Ideal Quantum Photodetection § Quantum Efficiency : § Direct Detection: measurement § Homodyne Detection: measurement § Heterodyne Detection: measurement

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Loss is a Problem for Squeezed States

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Coming Attractions: Lecture 11 § Lecture 11: Single-Mode and Two-Mode Linear Systems

§ Attenuators § Phase-Insensitive Amplifiers § Phase-Sensitive Amplifiers

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6.453 Quantum Optical Communication

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