Purdue University Spring 2014 Prof. Yong P. Chen Lecture 5 (2/3/2014) Slide Introduction to Quantum Optics & Quantum Photonics PHYS522 ECE695 (“Coherent Optics & Quantum Electronics”) Lecture 5 Quantum Information 1: Quantum Communication & Quantum Cryptography Note: HWK2 posted on course web, due next Wed 2/12 in class

Purdue University Spring 2014 Prof. Yong P. Chen Lecture 5 (2/3/2014) Slide Introduction to Quantum Optics & Quantum Photonics PHYS522 ECE695 (“Coherent Optics & Quantum Electronics”) Course Outline Part 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

Purdue University Spring 2014 Prof. Yong P. Chen Lecture 5 (2/3/2014) Slide Introduction to Quantum Optics & Quantum Photonics PHYS522 ECE695 (“Coherent Optics & Quantum Electronics”) This Lecture Quantum Information Science 1: quantum (secure) communication & quantum cryptography (photon based) (cf. *FQ Chap12) Shapiro-Wong Group: MIT course on quantum communication 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:

Purdue University Spring 2014 Prof. Yong P. Chen Lecture 5 (2/3/2014) Slide Introduction to Quantum Optics & Quantum Photonics PHYS522 ECE695 (“Coherent Optics & Quantum Electronics”) From :C. Bennett lecture “Information is quantum” [highly recommended to read] See also watch?v=tKfyw-uAgac

Purdue University Spring 2014 Prof. Yong P. Chen Lecture 5 (2/3/2014) Slide Introduction to Quantum Optics & Quantum Photonics PHYS522 ECE695 (“Coherent Optics & Quantum Electronics”)

Purdue University Spring 2014 Prof. Yong P. Chen Lecture 5 (2/3/2014) Slide Introduction to Quantum Optics & Quantum Photonics PHYS522 ECE695 (“Coherent Optics & Quantum Electronics”) Classical Cryptography (Secure Communication) ENIGMA RSA RSA-100 = RSA-100= × Earn $200,000 to factorize RSA-2048 Later quantum computing will break this

Purdue University Spring 2014 Prof. Yong P. Chen Lecture 5 (2/3/2014) Slide Introduction to Quantum Optics & Quantum Photonics PHYS522 ECE695 (“Coherent Optics & Quantum Electronics”) 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.

Purdue University Spring 2014 Prof. Yong P. Chen Lecture 5 (2/3/2014) Slide Introduction to Quantum Optics & Quantum Photonics PHYS522 ECE695 (“Coherent Optics & Quantum Electronics”) Classical communication & evesdropper

Purdue University Spring 2014 Prof. Yong P. Chen Lecture 5 (2/3/2014) Slide Introduction to Quantum Optics & Quantum Photonics PHYS522 ECE695 (“Coherent Optics & Quantum Electronics”) Photon polarization qbits

Purdue University Spring 2014 Prof. Yong P. Chen Lecture 5 (2/3/2014) Slide Introduction to Quantum Optics & Quantum Photonics PHYS522 ECE695 (“Coherent Optics & Quantum Electronics”) Review 2-state QM (d=2 Hilbert space) R 2 representation

Purdue University Spring 2014 Prof. Yong P. Chen Lecture 5 (2/3/2014) Slide Introduction to Quantum Optics & Quantum Photonics PHYS522 ECE695 (“Coherent Optics & Quantum Electronics”) Quantum No Cloning Theorem cse599d/06wi/lecturenotes4.pdf

Purdue University Spring 2014 Prof. Yong P. Chen Lecture 5 (2/3/2014) Slide Introduction to Quantum Optics & Quantum Photonics PHYS522 ECE695 (“Coherent Optics & Quantum Electronics”) QKD by BB84 Protocol (ex.12.3) Interesting read on B&B (also discovered q. teleportation)

Purdue University Spring 2014 Prof. Yong P. Chen Lecture 5 (2/3/2014) Slide Introduction to Quantum Optics & Quantum Photonics PHYS522 ECE695 (“Coherent Optics & Quantum Electronics”)

Purdue University Spring 2014 Prof. Yong P. Chen Lecture 5 (2/3/2014) Slide Introduction to Quantum Optics & Quantum Photonics PHYS522 ECE695 (“Coherent Optics & Quantum Electronics”)

Purdue University Spring 2014 Prof. Yong P. Chen Lecture 5 (2/3/2014) Slide Introduction to Quantum Optics & Quantum Photonics PHYS522 ECE695 (“Coherent Optics & Quantum Electronics”)

Purdue University Spring 2014 Prof. Yong P. Chen Lecture 5 (2/3/2014) Slide Introduction to Quantum Optics & Quantum Photonics PHYS522 ECE695 (“Coherent Optics & Quantum Electronics”) 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”

Purdue University Spring 2014 Prof. Yong P. Chen Lecture 5 (2/3/2014) Slide Introduction to Quantum Optics & Quantum Photonics PHYS522 ECE695 (“Coherent Optics & Quantum Electronics”) 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

Purdue University Spring 2014 Prof. Yong P. Chen Lecture 5 (2/3/2014) Slide Introduction to Quantum Optics & Quantum Photonics PHYS522 ECE695 (“Coherent Optics & Quantum Electronics”) Transmission Media for quantum communication/cryptography Subject to environmental noise (air turb. stray light etc.) Subject to loss and birefringence (at long distance) Phase (vs polarization) encoding

Purdue University Spring 2014 Prof. Yong P. Chen Lecture 5 (2/3/2014) Slide Introduction to Quantum Optics & Quantum Photonics PHYS522 ECE695 (“Coherent Optics & Quantum Electronics”)

Purdue University Spring 2014 Prof. Yong P. Chen Lecture 5 (2/3/2014) Slide Introduction to Quantum Optics & Quantum Photonics PHYS522 ECE695 (“Coherent Optics & Quantum Electronics”) See also : (  potential essay topic, explain how these work, or market analysis)

Purdue University Spring 2014 Prof. Yong P. Chen Lecture 5 (2/3/2014) Slide Introduction to Quantum Optics & Quantum Photonics PHYS522 ECE695 (“Coherent Optics & Quantum Electronics”) Quantum communication in space (use entanglement) (  another example potential essay topic, explain how this work)

Purdue University Spring 2014 Prof. Yong P. Chen Lecture 5 (2/3/2014) Slide Introduction to Quantum Optics & Quantum Photonics PHYS522 ECE695 (“Coherent Optics & Quantum Electronics”) QKD based on entanglement (Eckert protocol)

Purdue University Spring 2014 Prof. Yong P. Chen Lecture 5 (2/3/2014) Slide Introduction to Quantum Optics & Quantum Photonics PHYS522 ECE695 (“Coherent Optics & Quantum Electronics”) Entanglement based QKD Entanglement’s Benefit Survives an Entanglement-Breaking Channel Zheshen Zhang, Maria Tengner, Tian Zhong, Franco N. C. Wong, and Jeffrey H. Shapiro Phys. Rev. Lett. 111, (2013) Viewpoint: Don’t Cry over Broken Entanglement 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).Science 321, 1463 (2008) A modern example

Purdue University Spring 2014 Prof. Yong P. Chen Lecture 5 (2/3/2014) Slide Introduction to Quantum Optics & Quantum Photonics PHYS522 ECE695 (“Coherent Optics & Quantum Electronics”) Next Lecture (5): Light Matter Interaction --- Radiative Transition in Atoms FQ Chap 4