lecture 5 quantum information 1: quantum communication & quantum cryptography

Purdue University Spring 2014 Prof. Yong P. Chen ([email protected]) Lecture 5 (2/3/2014) Slide 1

Introduction to Quantum Optics & Quantum Photonics

PHYS522 ECE695

(“Coherent Optics & Quantum Electronics”) http://www.physics.purdue.edu/academic_programs/courses/phys522/

Lecture 5Quantum Information 1:

Quantum Communication & Quantum Cryptography

Note: HWK2 posted on course web, due next Wed 2/12 in class



PHYS522 ECE695


Lectures Topics Lecture 1 (1/13) Overview (FQ1+) Lecture 2 (1/15) Review Classical Optics (FQ2; FS1-2) No Class on 1/20 Monday (MLK day) Lecture 3 (1/22) Review Quantum Mechanics, birth of photons (FQ3+) Lecture 4 (1/27) Quantum Information, cryptography & communication (FQ12) Lecture 5 (1/29) Radiative Transitions in Atoms & Molecules (FQ4; FS8.2) Lecture 6 (2/03) Radiative/Inter-band transition in solids (FS3, FS7.3.2) Lecture 7 (2/05) Masers & Lasers: CW, pulsed, frequency comb, Xasers Lecture 8 (2/10) Photon Statistics (FQ5) Lecture 9 (2/12) Photon Correlation (FQ6), extension to other (quasi)particles Lecture 10 (2/17) Coherent, Squeezed & Number states (FQ7,8) Lecture 11 (2/19) Resonant Light-atom interaction, density matrices, Rabi oscillation (FQ9) Lecture 12 (2/24) Solid state quantum structures: wells, wires and dots (FS6) Lecture 13 (2/26) Laser cooling of atoms & solids (FQ11+) Lecture 14 (3/03) Cold atoms & atom optics, atom lasers (given by TA R. Niffenegger) Lecture 15 (3/05) TBD (Special topics/APS/coherent control) Lecture 16 (3/10) Excitons and Polaritons (FS4+) Lecture 17 (3/12) Luminescence, Luminescence/NV centers & quantum emitters (FS5,9+) No classes on 3/17 & 3/19 (Spring Break) Lecture 18 (3/24) EIT, slow light (Agarwal) & coherent control Lecture 19 (3/26) Quantum entanglement, memory & teleportation (FQ14) Lecture 20 (3/31) Atoms in cavities, Jaynes-Cummings model (FQ10) Lecture 21 (4/02) Cavity QED/circuit QED, optomechanics Lecture 22 (4/07) Quantum Computing, photon based QC (FQ13+) Lecture 23 (4/09) Quantum Computing systems: ions, Rydberg atoms, molecules Lecture 24 (4/14) Quantum Computing systems: superconductor/cQED, quantum dots, NMR Lecture 25 (4/16) Photonics with nanomaterials: CNT, graphene & 2D materials (FS8+) Lecture 26 (4/21) Phonons/Vibrons and Raman spectroscopy, CARS (FS10) Lecture 27 (4/23) Special topics: Quantum Sensing & Photodetectors, applications Lecture 28 (4/28) Special topics: Optically synthetic gauge fields/topological/quantum

matter, quantum emulation, student presentations Lecture 29 (4/30) Special topics: Casimir, (quantum) plasmonics etc. student presentations Final Exam on (TBD)

Course OutlinePart 1: basic review:Optics+Quantum;

Part 2: Basic Light-matter interaction; laser;

Part 3: Quantum Optics of photons

Part 4: More advanced light-matter interaction

Part 5: Quantum information/photonics/applications

Subject to change;Check updates on course web/wiki



PHYS522 ECE695


This Lecture• Quantum Information Science 1: quantum (secure)

communication & quantum cryptography (photon based) (cf. *FQ Chap12)

Shapiro-Wong Group: http://www.rle.mit.edu/qoptics/

MIT 6.453 course on quantum communicationhttp://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-453-quantum-optical-communication-fall-2008/

Learn more:

M. Le Blanc: A Short Introduction to Quantum Information and Quantum ComputationChuang & Nielson, QCQIDavid Mermin, Quantum Computer Science: An Introduction

Good to reach on beach or train: J. Dowling’s Schrodinger’s Killer AppL. 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: http://quantuminformation.physi.uni-heidelberg.de/pic/LEC430.pdf



PHYS522 ECE695


http://researcher.watson.ibm.com/researcher/files/us-bennetc/QInfWeb.pdfFrom :C. Bennett lecture “Information is quantum” [highly recommended to read]

See also http://www.youtube.com/watch?v=tKfyw-uAgac



PHYS522 ECE695




PHYS522 ECE695


Classical Cryptography (Secure Communication)

ENIGMA

RSARSA-100 =15226050279225333605356183781326374297180681149613 80688657908494580122963258952897654000350692006139

RSA-100=37975227936943673922808872755445627854565536638199× 40094690950920881030683735292761468389214899724061

Earn $200,000 to factorize RSA-2048

Later quantum computing will break this



PHYS522 ECE695


The purpose of quantum cryptography is toprovide a reliable method for transmitting a secret key and knowing thatno-one has intercepted it along the way.

The method is founded on thefundamental 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.



PHYS522 ECE695


Classical communication & evesdropper



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Photon polarization qbits



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Review 2-state QM (d=2 Hilbert space)

R2 representation

1 0,

0 1

y

x

11 1( )

12 2

11 1( )

12 2

1 1( ), ( )

2 2



PHYS522 ECE695


Quantum No Cloning Theorem

http://courses.cs.washington.edu/courses/cse599d/06wi/lecturenotes4.pdf

U



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QKD by BB84 Protocol

(ex.12.3)

http://researcher.watson.ibm.com/researcher/view.php?person=us-bennetc

http://www.noodls.com/view/C72E62DBAF2DB94324F14C95042A47D40F3E72EF

Interesting read on B&B

(also discovered q. teleportation)

http://www1.cse.wustl.edu/~jain/cse571-07/ftp/quantum/index.html



PHYS522 ECE695




PHYS522 ECE695


Reality Complications

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

Reduced key length

General Read: “Quantum cryptography: Seeking absolute security”http://www.nature.com/nature/journal/v447/n7143/full/447372a.html



PHYS522 ECE695


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



PHYS522 ECE695


Transmission Media for quantum communication/cryptography

Subject to environmental noise (air turb. stray light etc.) <possible project/essay>

Subject to loss and birefringence (at long distance)

Phase (vs polarization) encoding



PHYS522 ECE695




PHYS522 ECE695


See also : http://qwcap.com

(potential essay topic, explain how these work, or market analysis)



PHYS522 ECE695


Quantum communication in space

http://www.nature.com/news/data-teleportation-the-quantum-space-race-1.11958

(use entanglement)

(another example potential essay topic, explain how this work)



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QKD based on entanglement

(Eckert protocol)



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Entanglement based QKD

Entanglement’s Benefit Survives an Entanglement-Breaking ChannelZheshen Zhang, Maria Tengner, Tian Zhong, Franco N. C. Wong, and Jeffrey H. ShapiroPhys. Rev. Lett. 111, 010501 (2013)

Viewpoint: Don’t Cry over Broken Entanglement

http://physics.aps.org/articles/v6/74

A secure communication channel that relies on quantum entanglement survives despite the noisy break up of the entanglement itself.

Related to idea of “quantum illumination” (entanglement enhanced quantum sensing/detection) S. Lloyd, “Enhanced Sensitivity of Photodetection via Quantum Illumination,” Science 321, 1463 (2008).

A modern example



PHYS522 ECE695


Next Lecture (5): Light Matter Interaction --- Radiative Transition in Atoms

• FQ Chap 4

lecture 5 quantum information 1: quantum communication & quantum cryptography

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