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“ Anyone who can contemplate quantum mechanics without ge “ Anyone who can contemplate quantum mechanics without ge

“ Anyone who can contemplate quantum mechanics without ge - PowerPoint Presentation

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“ Anyone who can contemplate quantum mechanics without ge - PPT Presentation

t understood it Niels Bohr The Quantum Information Revolution Paul Kwiat DARPA Kwiats Quantum Clan 2012 Graduate Students Rebecca Holmes Aditya Sharma ID: 619245

000 quantum light photon quantum 000 photon light key information cryptography photons state atom number interference object factoring science

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Slide1

Anyone who can contemplate quantum mechanics without getting dizzy hasn

t understood it.

--Niels BohrSlide2

The Quantum Information Revolution Paul Kwiat

DARPASlide3

Kwiat’s

QuantumClan (2012)Graduate Students:

Rebecca Holmes

Aditya Sharma

Trent Graham Brad Christensen

Kevin Zielnicki

Mike Wayne

Courtney Byard

Undergraduates: Daniel Kumor

David

Schmid Jia Jun (“JJ”) Wong

Cory

Alford Joseph Nash David RhodesVisit Prof: Hee Su ParkPost-Doc: Jian WangSlide4

A New Science!

Quantum

Mechanics

Information

Science

Quantum Information Science

20th Century

21st Century

Slide5

Quantum

Information

Fundamental physics

Decoherence

Quantum

classical

Entanglement

Ultimate control over

large

systems

Quantum metrology

Measurements beyond

the classical limit

Non-invasive measurements

Measurements on quantum

systems

Quantum cryptography

Secure key distribution

(even between

non-speaking parties)

Quantum computation

Factoring

Simulating other quantum

systems (>30bits)

Error correction

Quantum communciation

Teleportation

Linking separated

quantum systems

(

q. network

)Slide6

Quantum Metrology

Quantum Computing

Quantum CryptographySlide7

Things should be made as simple as possible, but not any simpler.”Slide8

What

I do…Unravel the mysteries of the universe…

Quantum Optics

Light

???Slide9

Quantum…

very smallvery big (e.g., “quantum leap”)

an unsplittable parcel/bundle of energy

a cool buzzword to get more funding, more papers, more people at your Sat. am physics lecture, etc.all of the aboveSlide10

1905: Einstein made a ‘quantum leap’ and proposed that light was really made of particles with tiny energy given by

E = h f = h c/l

frequency

6.6 x 10

-34

J-s

wavelengthSlide11

Power input

Partially transmitting mirror

How many photons per second are emitted from a

1-mW

laser (

l

=635nm

)?

How do we reconcile this notion that light comes in

packets

with our view of an electromagnetic wave, e.g., from a laser??

Power output: P = (# photons/sec) x E

photon

Visible light

Physics 214: Lect. 7

Example

:

“Counting photons”Slide12

1

mW red laser3 x 1015 photons/sec =

This is an incredibly huge number – your eye basically cannot resolve this many individual photons (though the rods can detect single photons!

). And

you MAY be able to see just one photon!!

3,000,000,000,000,000/sec

Slide13

Formation of Optical Images

For large light intensities

, image formation by an optical system can be described by classical optics.

Exposure time

However,

for very low light intensities

, one can see the statistical and random nature of image formation.

Use an extremely sensitive CCD camera that can detect single photons.

A. Rose, J. Opt. Sci. Am. 43, 715 (1953)Slide14

"God does not play

dice with the universe."

“It seems to me that the idea of a personal God is an anthropological concept which I cannot take seriously.

Photon only detected in one output.

Equally likely to be transmitted or reflected

cannot tell which.

A

beamsplitter…

But how do we *know* there’s only ONE photon…

Quantum random-number generator!completely unpredictablepatentedcommercially available“0”“1”Slide15

The important thing is not to stop questioning.” -A. EinsteinSlide16

Quantum

Interrogation

Yes, yes, already, Warren! … There

is film in the camera!”

The problem…

Measure

-film -absorber

-atom without -exposing -heating

-exciting itSlide17

WHY was Einstein’s 1905 proposal that light was made of particles such a profound leap

that almost no one believed him?Because everyone KNEW that light was really waves.One of the strangest features of QM: all particles can behave like waves…Slide18

Interference of

waves (e.g., water, sound, …)Slide19

Superposition (adding together)

of wavesWaves add up:“Constructive interference”

Waves cancel:

“Destructive interference”Slide20

Light:

Particle or Wave?

1675: Newton

proved” the light was made of “corpuscles”

1818: French Academy science contest

Fresnel proposed interference of light.Judge Poisson

knew light was made of particles: “Fresnel’s ideas ridiculous” If Fresnel ideas were correct, one would see a bright spot in the middle of the shadow of a disk.Slide21

Judge Arago decided to actually do the experiment…

Conclusion (at the time):

Light

must be a wave, since particles don’t interfere!

Only, now we know

that they must!Slide22

Single-Photon

Interference:Question: what if we reduce the source intensity so that at most one particle (photon) is in the apparatus at a time?

Exposure time

Answer:

Just like in the

optical image formation

, given enough time, the

classical interference pattern

will gradually build up from a huge # of seemingly random

“events”!

Photons

?Slide23

Optical Interferometers

Interference arises when there are two (or more) ways for something to happen, e.g.,

sound from two speakers reaching your ear.

An interferometer is a device using mirrors and “beam splitters” (half light is transmitted, half is reflected) to give two separate paths for light to get from the source

to the detector.

Two common types: Mach-Zehnder:

Michelson :

mirror

beam-

splitter

beam-

splitter

mirrorSlide24

Quantum

Interrogation

Yes, yes, already, Warren! … There

is film in the camera!”

The problem…

Measure

-film -absorber

-atom without -exposing -heating

-exciting itSlide25

The solution…

(Elitzur & Vaidman

, 1993)Use

dual wave-particle nature of quantum objects (“wavicles”)

Single photon always shows up at D1

(complete destructive interference to D2)Slide26

Now place an absorbing object in one arm…

50% chance that photon is absorbed by object

50% chance it isn

’t  25% chance D2 fires 

“interaction-free measurement

” of objectSlide27

Quantum Interrogation

Optimizing

reflectivities

 50% efficiencyBy combining these techniques with the

“quantum Zeno effect” (making repeated very weak interactions), the efficiency can in principle be pushed to 100%: no photons absorbed by the absorbing object!

[85% demonstrated to date]

Imaging semi-transparent objects does not readily yield a gray-

scaleSlide28

Quantum Metrology

Quantum Computing

Quantum Cryptography

Wpdrval

L&wz;xcuymnzx

Slide29

Cryptography:

Make messages so that only the intended recipient can understand them…public key encryption: Standard, but not provably secure; relies on difficulty of factoring (e.g., 15 = 3x5)

secret key encryption: PROVABLY secure as long as no one else has the key

the key is never reused

Quantum Cryptography = Quantum Key DistributionSlide30

ALICE

BOB

Cipher:

…0110010110100010…

XOR(Cipher,Key)

Message

EVE

KEY:

…010001010011101001…

Quantum Cryptography

Cryptography

XOR(Message,Key)

CipherSlide31

Quantum Cryptography:

Use a different property of light– polarization!Prob(horizontally polarized photon pass horizontal polarizer): 1

Polarization: --the oscillation direction of the light--property of each photon

--can measure with polarizers, calcite, etc.

Prob(horizontally polarized photon pass vertical polarizer): 0

Prob

(diagonally pol. photon pass horizontal polarizer): 1/2

Prob

(diagonally pol. photon pass vertical polarizer): 1/2Slide32

How to Make

“Entangled” Coins

We don’t know WHICH crystal created the pair of photons, but we know they both came from the

same

crystal

 they

MUST have the same polarization.

“Spontaneous

DownConversion

”:

high energy parent photon can split into two daughter photons(with same polarization)Slide33

Entangled-Photon Quantum Cryptography

Alice & Bob randomly measure polarization in the (HV) or the (45 45) basis.

Discuss via a

public channel

which bases they used,

but not the results. Discard cases (50%) where they used different bases 

uncorrelated results. Keep cases where they used the same basis  perfectly correlated results! Define H “0

45, V “1”



45. They now share a secret key.Slide34

Eve cannot

“tap” the line

 photons that don’t make it to Bob are not part of the key

Eve cannot “clone” the photon

 forbidden by basic quantum mechanics

Measurements by Eve necessarily have a chance (25

%) to disturb the quantum state

 Alice and Bob can detect errors in the key!

If the bit error rate is too high, they simply discard the key. No message is ever compromised.What about Eavesdropping?Slide35

Current Free-Space QKD Distance Record: 144

km between LaPalma and Tenerife

Last week news item: they used the entangled photons to teleport the state of a photon between the islands – world distance record for quantum teleportation!Slide36

QKD Goes Commercial…Slide37

Since we can seemingly

“see” without “

looking” using quantum interrogation, does this mean an eavesdropper could use it to defeat quantum cryptography?

No! It turns out that even making the gentlest measurement possible, if the eavesdropper gains any information, she disturbs the state.Or if she is so gentle so as not to disturb the state, then she gets no information.Quantum key distribution is secure against any

attack allowed by the laws of physics!

Quantum Interrogation vs.

Quantum CryptographySlide38

Imagination is more important than knowledgeSlide39
Slide40

Source: Intel

Moore

s LawSlide41

The first solid-state transistor

(Bardeen, Brattain & Shockley, 1947)Slide42

INTEL

Pentium 4

transistor

The Ant and

the Pentium

~100 million transistors

Size of an atom

~ 0.1nmSlide43

Superposition

Interference

Wave-particle duality

Intrinsic randomness in measurement

Entanglement

2-level atom

:

ge

 spin-1/2: 

polarization:

HV

Binary digit Quantum bit “bit” “qubit” 0, 1 0101

Physical realization of qubits

any 2 level system

All 2-level systems are created equal, but some are more equal than others!

Quantum communication

photons

Quantum storage

atoms, spins

Scaleable

circuits

superconducting

systems

Quantum

phenomenaSlide44

Entanglement”, and the scaling that results, is the key to the power of quantum computing.

Classically

, information is stored in a bit register: a 3-bit

register can store

one

number, from 0 – 7.

a

|

000

ñ

+ b

|

001

ñ

+ c

|

010

ñ

+ d

|

011

ñ

+ e

|

100

ñ

+ f

|

101

ñ

+ g

|

110

ñ

+ h

|

111

ñ

Result:

--

Classical:

one N-bit number

--

Quantum:

2

N

(all possible) N-bit numbers

N.B.

:

A 300-

qubit

register can simultaneously store

2

300

~ 10

90

numbers

1

0

1

Quantum Mechanically

, a register of 3 entangled

qubits

can store all of these numbers in superposition:Slide45

That’s a BIG number

1090

=

This is more than the total number of particles in the Universe!

1,000,000,000,000,000,000, 000,000,000,000,000,000

, 000,000,000,000,000,000

, 000,000,000,000,000,000, 000,000,000,000,000,000

Some important problems benefit from this exponential scaling, enabling solutions of otherwise insoluble problems. Slide46

A hard problem: factoring large integers

:

For example, it is hard to factor 167,659

But an elementary school student can easily multiply 389 x 431 = 167,659

This asymmetry in the difficulty of factoring vs. multiplying is the basis of public key encryption, on which everything from on-line transaction security to ensuring diplomatic secrecy depends.Slide47

Quantum Computing

’s “killer app.”

RSA

digitsPC(1 GHz)Blue Waters

(10PF)Quantum Computer (1 GHz)

1294 months1 sec

10 sec225300,000 yr

12 days100 sec3001016 yr

(>> universe)20 million yr200 secThe difficulty (impossibility) of factoring large numbers (and the ease of creating a large number from its factors) is the basis of public key encryption (which nearly everyone uses for secure transmission today). Quantum algorithms enable one to factor numbers into their prime constituents MUCH faster:Slide48

state labels

”, “ ”

Atom in different energy states:

atom

energy states:

atom in

state

atom in

state

atom in

superposition state

shorthand

wave function

representation

=

 

+



Probability of measuring , P

= |

|

2

Probability of measuring , P

= |

|

2Slide49

|0

|0

+ |1

|0

|0

|1

|rest

state of motion

Collective motion: the

quantum data bus

laser

|0

|0

|0

|0

|1

|rest + |movingSlide50

Science News

Quantum Computing ExploredSep 12 2001 @ 08:10

American computer scientists are studying the possibility to build a super fast computer based on quantum physics. Slide51

Technology requirements

Set of qubits isolated from environment.

“Quantum information bus” to connect qubits.

Reliable read-out method.

Essential DichotomyNeed WEAK coupling to environment to avoid decoherence, but you also need STRONG coupling to at least some external modes in order to ensure high speed and reliability.

Why it might not work…Slide52

Quantum Information Timeline

0 5 10 ~15 20? 25??

Time (years)

Difficulty/Complexity

Quantum

Measurement

Quantum

Communication

The known

Quantum

Computation

The expected

The unlikely – impossible?

Quantum

Sensors?

The as yet unimagined!!!

Quantum

Engineered Photocells?

Quantum

Widgets

Quantum

Games & ToysSlide53

Why is it that nobody understands me, and everybody likes me?” – A.E.Slide54

Quantum Imaging

No object:

photon leaves

45˚-polarized

no counts at D

2

Object blocks beam:

photon leaves

H-polarized  counts at D2

Scan object through

beam waist  micron resolution Slide55

Reduced Absorption

“Imaging”

Detecting the object with less than one photon!Slide56

Interconnected multi-trap structure

Route ions by controlling electrode potentials

Processor sympathetically cooled

No individual optical addressing during two-qubit gates

(can do gates in strong trap  fast)

One-qubit gates in subtrapReadout in subtrap

Multiplexed Ion Trap Architecture

control electrodesSlide57

Quantum factoring and cryptography

Classical

~ e

AL

# of instructions

# of bits, L, factored

Quantum

~

L

3

RSA129

~ 10

9

operations:

seconds

~ 10

17

instructions:

8 months

the RSA cryptosystem:

polynomial

work to encrypt/decrypt

exponential

work to break = factoring

BUT quantum factoring is only

polynomial work

latency

: will information encrypted today be secure against future quantum computers?Slide58

Quantum Mechanics and Information Science were two of the most important and revolutionary developments of the 20th century:

Quantum Mechanics

changed the way we think about the physical world and enabled a wealth of new technology, including lasers, solid state electronics--the foundations of much of what we identify with modern life.

Information Science changed the way we think about “thinking.” Digital information processing is ubiquitous in communication, entertainment, commerce, manufacturing, science…And its implementation has depended on the devices of quantum mechanics.