1. Lecture 21 Photon Statistics (detecting sub-poissoinian light) application 1 of single photons: quantum communication
Read: FQ5, FQ12

2. Quantum Optics of Photons
FQ’Chap5
FQ’Chap6
Chap 7-8: coherent, squeezed, & number states

3. Photon Statistics FQ’Chap5 Single photon detector:
PMT (photomultiplier tube)
APD (avalanche photodiode)

4. Subpoissonian Light But: any (random) loss will randomize the photons
(det. Subpoissonian challenging)

5. Theory of Photodetection (semiclasical)
If I(t)=I constant
If I(t) fluctuating, superpoissonian

6. Theory of Photodetection (quantum)
But: any (random) loss will
randomize the photons
(det. Subpoissonian challenging)
Key: high Q.E.

7. Noise in Photodiodes

8. Shot Noise (“quantum noise”)

10. (classical) Noise Reduction
Also: feed-forward

11. Experimental Observation of quantum nature of light: sub-poissonian light
Use sub-poissonian electrons to gernerate SubP-light
Sub-poissonian
counting statistics

12. Sub-shot noise photocurrent

13. Shapiro-Wong Group: http://www.rle.mit.edu/qoptics/
Quantum Information Science 1: quantum (secure) communication & quantum cryptography (photon based) (cf. *FQ Chap12)
Learn more:
M. Le Blanc: A Short Introduction to
Quantum Information and Quantum Computation
Chuang & Nielson, QCQI
David Mermin, Quantum Computer Science: An Introduction
Good to reach on beach or train: J. Dowling’s Schrodinger’s Killer App
L. Susskind, Quantum Mechanics: The Theoretical Minimum
(see also Stanford course lectures/videos of same title)
N. Gisin et al. Rev. Mod. Phys. 74, 145–195 (2002)
J.W.Pan Lecture:
MIT course on quantum communication
Shapiro-Wong Group:

14. See also
watch?v=tKfyw-uAgac
From :C. Bennett lecture “Information is quantum” [highly recommended to read]

16. Classical Cryptography (Secure Communication)
ENIGMA
RSA-100= ×
Earn $200,000 to factorize RSA-2048
Later quantum computing
will break this
RSA
RSA-100 =

17. The purpose of quantum cryptography is to
provide a reliable method for transmitting a secret key and knowing that
no-one has intercepted it along the way.
The method is founded on the
fundamental laws of quantum physics, and the process of sharing a secret key in a secure way is called quantum key distribution.
Two basic schemes for quantum cryptography, using
basic principles of quantum measurements on single particles (photons)
The properties of entangled photon properties of entangled states.

18. Classical communication & evesdropper

19. Photon polarization qbits

20. Review 2-state QM (d=2 Hilbert space)
R2 representation

21. Quantum No Cloning Theorem
cse599d/06wi/lecturenotes4.pdf

22. QKD by BB84 Protocol (ex.12.3) Interesting read on B&B
At 57, Gilles Brassard has won a multitude of awards, but the Nobel Prize would be a crowning achievement at an international level. The young mathematics prodigy initially discovered by his brother Robert, his elder by six years, Brassard mastered differential and integral calculus in elementary school. Université de Montréal opened its door to Brassard when he was just 13 years old, and he entered into a bachelor's program. The "mathematical elegance" of cryptography captivated him during his doctoral studies at Cornell University, and he immediately redirected his attention to the science of coding, until then the preserve of the military.
His meeting with Charles Bennett in November 1979 was decisive and is the stuff of cinema. A few days before delivering a lecture on cryptography in Puerto Rico, Brassard was bathing in the ocean when he saw a stranger swimming toward him. The man approached him saying that he knew how to duplicate banknotes that are otherwise impossible to duplicate, using quantum mechanics. "That meeting in the middle of the ocean changed my life," says Brassard.
Twelve years his elder, Bennett had read the title of Brassard's paper in the program and wanted to meet him. The two men became friends and worked together actively, leading to a famous brainstorming session in November Inspired by an article on quantum physics he had just read, Brassard invited one of the authors, William Wootters, to present his findings in Montreal. He took the occasion to invite Charles Bennett and Claude Crépeau. During the presentation, a question was raised by Bennett that Wootters was unable to answer. The researchers locked themselves in Brassard's office to discuss the matter. "Twenty-four hours later, the theory of quantum teleportation was born," recalls the scientist.
Returning to their daily lives, the researchers exchanged papers between North America, Europe, and Israel: according to Brassard, the six authors were in a continuum of movement on which the sun never set. It took only 11 days to prepare and submit the article. "I think the principle of quantum teleportation would have been discovered sooner or late because it was inevitable. Our collaboration saved a few years," he says.
Never tiring of his teaching career after 33 years - first as lecturer at the University at 24, then as full professor nine years later, becoming the youngest faculty member to receive such a promotion in the modern history of the Université de Montréal - Gilles Brassard relishes the freedom afforded by his position. As head of the Canada Research Chair in quantum computing, he continues his work in theoretical and quantum computer science. He currently supervises some ten graduate students, mostly doctoral candidates, half of whom are from abroad. His greatest professional pride comes from learning that a former student has obtained a professorship at a university somewhere in the world, a pleasure he has known more than twenty times already.
Without hesitation, he refuses offers from abroad, enjoying above all the quality of life of Montreal, his hometown. An avid cyclist and hiker, the Nobel contender also loves cooking and listening to music. Most of all, he has an undying sense of humour, peppering his remarks on quantum physics with spontaneous laughter.
- See more at:
Interesting read on B&B
(also discovered q. teleportation)

26. Reality Complications
Reduced key length
Missing photons .. Reduce # of useful bits
Birefringence (change polarization during transmission)
Detector dark counts (false click even with missing photons)
address by
(classical)
Error
correction
General Read: “Quantum cryptography: Seeking absolute security”

27. Hardware requirements/complications
(reliable) Single photon source
[multiphoton emission compromises security by giving Eve more chances to evade detection (both Eve’s detectors click  knows basis wrong)]
Attenuated single-freq laser: photon Poisson distr, subject to multi-photons
“on-demand” single photon source [current research]
(will revisit this when discussing QO)
(reliable) single photon detectors, polarization rotators, medium

28. Transmission Media for quantum communication/cryptography
Subject to environmental noise (air turb. stray light etc.)
<possible project/essay>
Phase (vs polarization) encoding
Subject to loss and birefringence (at long distance)

30. See also : http://qwcap.com
(potential essay topic, explain how these work, or market analysis)