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6.453 Quantum Optical Communication
Spring 2009
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October 14, 2008
6.453 Quantum Optical Communication
Lecture 10
Jeffrey H. Shapiro
Optical and Quantum Communications Group
www.rle.mit.edu/qoptics
6.453 Quantum Optical Communication - Lecture 10
! Announcements
! Turn in problem set 5
! Pick up problem set 4 graded, problem set 5 solution, problem set 6,
lecture notes, slides
! Single-Mode Photodetection
! Signatures of non-classical light
! Squeezed-state waveguide tap
2
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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
,
3
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Single-Mode Quantum Photodetection
! Photon-Units Field Operator:
for
! Direct Detection:
measurement
! Homodyne Detection:
! Heterodyne Detection:
measurement
measurement
4
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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
5
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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
6
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Optical Waveguide Tap —!Semiclassical
! Coupler is a beam splitter
Fused Fiber Coupler
! Tap input is zero
! Homodyne SNR at signal input
! Homodyne SNR at signal output
! Homodyne SNR at tap output
7
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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
8
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Optical Waveguide Tap: SNR Tradeoff
9
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Non-Ideal Quantum Photodetection
! Quantum Efficiency
! Direct Detection:
:
measurement
! Homodyne Detection:
! Heterodyne Detection:
measurement
measurement
10
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Loss is a Problem for Squeezed States
11
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Coming Attractions: Lecture 11
! Lecture 11:
Single-Mode and Two-Mode Linear Systems
! Attenuators
! Phase-Insensitive Amplifiers
! Phase-Sensitive Amplifiers
12
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