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Dimitris G. AngelakisAssistant Professor

School of Electronic and Computer Engineering,

Technical University of Crete

Quantum physics and quantumtechnologies: From physical theories to

quantum computing machines

Electronicand

Computer

Engineering,

Technical

University ofCrete

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Quantum optics and quantum information team

Dimitris G. Angelakis (group leader)

Changsuk Noh (post-doc,CQT)

Priyam Das (post-doc, CQT)Amit Rai (post-doc, CQT)Changyoup Lee (post-doc, CQT)

Nikos Shetakis (PhD student, TUC)

Mihalis Kalogerakis (PhD student, TUC)

MingXia Huo (PhD student, CQT)Markela Tsafantaki (MSc Student, TUC)

?

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Quantum Mechanics and Information Science

were two of the most important and revolutionary

developments of the 20th century:

Quantum Mechanicschanged the way we think aboutthe physical world and enabled a wealth of new

technology, including lasers, solid state electronics--thefoundations of much of what we identify with modern life.

Information Sciencechanged the way we think about

thinking. Digital information processing is ubiquitousin communication, entertainment, commerce,

manufacturing, science!And its implementation has

depended on the devices of quantum mechanics.

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A New Science!

Quantum

Mechanics InformationScience

Quantum Information Science

20th Century

21st Century

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The abacus is probably theearliest calculating tool.Earliest record: Babyloniansfollowed by the Chinese andthe Greeks

Ancient calculators

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Around 1617, John Napierinvented a calculating

device called Napiers

Bones

From the abacus to Napier bones

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Middle ages and renaissanceCalculators: Napier bones 1617

6x425=?

6x425=2550!

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From the abacus to the Antikythera mechanism:A 1st century BC planet motion calculator!

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In 1671, GottfriedWilhelm von

Leibniz inventeda computer that

was built in 1694.It could add, and,

after changing

some thingsaround, multiply.

Leibniz invented

a special steppedgear mechanism

1600s and mechanical calculators

He also co-invented calculus! His notation for

integration and differentiation still used today!

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William Oughtred invented the slide rule in 1500s.

This simple mechanical calculator was used until veryrecently!in fact as recently as the early seventies!

Victorian times and mechanical calculators

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08 July 2010

... I was sitting in therooms of the AnalyticalSociety, at Cambridge, my

head leaning forward onthe table in a kind of

dreamy mood, with a tableof logarithms lying openbefore me. Another

member, coming into the

room, and seeing me halfasleep, called out, Well,Babbage, what are youdreaming about?" to which

I replied "I am thinking thatall these tables" (pointingto the logarithms) "might

be calculated bymachinery."

1800s and Babbages engine:A logarithm calculator!

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... if I survive some few years longer, theAnalytical Engine will exist...

Analytical machine

Babbage describes five

logical components, thestore, the mill, thecontrol, the input and the

output.

Babbages engine: A logarithm calculator!

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Hollerith deskconsisted of a

card readerwhich sensed the

holes in thecards, a gear

drivenmechanismwhich could

count

Preparation of punched cards for theU.S. census

1900s engines based on cards with holes

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John Bardeen, WalterBrattain and William

Shockley

TransistorIntegrated circuit

Electronics era: The revolution of theTransistor in 1950s

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Harvard Mark I computer whichwas built as a partnership

between Harvard and IBM in1944

British Colossus

1940 USA (ENIAC- ElectronicNumerical Integrator And Computer)

filled a 20 by 40 foot room, weighed 30tons, and used more than 18,000

vacuum tubes. 10- by 10-digitmultiplication took 14 cycles, or 2800

microsecondsa rate of 357 per

second.

From electro-mechanical computers to electronic

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Microprocessors

SILICON WAFER

10-6 meters

Miniaturization

More components in a unit volume

more information per volume

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Towards the quantum limit

Quantum technology

Every 18 months microprocessors double in speedFASTER = SMALLER

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How small can they

be?

10-6

meters 10-8

meters10-10 meters

TODAY TOMORROW

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Quantum Technology!?

The extreme miniaturization allows for much more thanjust cramming many more bits in tiny regions.

The behaviour of nature in the microscale follows the lawsof Quantum Mechanics!

Quantum systems such as electrons, atoms, photonscan be at more than one physical state at a time as they

are particles and waves simultaneously.

Simultaneously????

f

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Images of

Quantum World

Electrons on the surface of a piece ofcopper are bound by 48 iron atoms

(the spikes at the perimeter)

STM picture IBM

Glowing and vibrating beryllium ionsin a linear ion trap.

Innsbruck University

14 nm

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Playing with photons

and ions

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Anyone who can contemplatequantum mechanics without gettingdizzy hasnt understood it.

--Niels Bohr

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Things should

be made assimple as

possible, but not

any simpler.

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Double slit experiment-particles

Machine gun firing rounds

at wall.

Number of bullets landing on

the screen when lower hole isclosed.

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Double slit experiment-particles

Both open.Upper hole closed.

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Double slit-waves

Water waves created by taping

on the surface of the water.

Wave energy arriving at the

coast when lower hole is clo

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Double slit-waves

Wave energy arriving atcoast when upper hole

is closed.

Wave energy arriving at

coast when both open.

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Double slit-electrons.

Electrons in a TV picture tubegoing through two slits

landing on a screen.

Distribution of 10 electrons fir

one by one.

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Double slit-electrons.

Electrons in a TV picture tubegoing through two slits

landing on a screen.

Distribution of 25 electrons fir

one by one.

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Double slit-electrons.

Electrons in a TV picture tubegoing through two slits

landing on a screen.

Distribution of 100 electrons fi

one by one.

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Double slit-electrons.

Electrons in a TV picture tubegoing through two slits

landing on a screen.

Distribution of 1000 electrons fione by one. Electrons behave a

waves, going through

both slits at once!!!

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Atoms as (classical) bits

+

-

+

-

STATE

STATE

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Classical registers-

only one bit can be stored and processed at any time!

+

-

+

-

+

-

Quantum superpositions or

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Quantum superpositions or

two different things in one?

An old woman smiling A young lady with her head

turned

?

What do you see?

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Quantum Registers

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Quantum superposition and measurements

in a superposition

young

old

measurement

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Quantum Power

0 0 0

0 0 1

0 1 0

1 1 1

0

0 1 1

11

1 1

1

0

0 0

Cl i l t

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Classical vs. quantumcomputation

0 0 0

0 0 1

0 1 0

0 1 1

1 0 0

1 0 1

1 1 0

1 1 1

0

0

1

0

0

1

0

1

1quantum compute F( )

compute F(000)

compute F(001)

compute F(010)

compute F(011)

compute F(100)

compute F(101)

compute F(110)

compute F(111)

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Quantum speed-up

Quantum computers are much fasterQuantum computers can solve someproblems which are too difficult forclassical computers

Quantum computers can breakcryptographic systems based on primenumber factorization!

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!"#$% '#()*"+ *% ,-./)-0 1*02-3/4 5)'$*"+ 2.")6!1982 - Feynman proposed the idea of creatingmachines based on the laws of quantum mechanicsinstead of the laws of classical physics.

! I think I can safely say that nobody understandsquantum mechanics- Feynman

! 1985 - David Deutsch developed the quantum turingmachine, showing that quantum circuits are universal.

! 1994 - Peter Shor came up with a quantum algorithm tofactor very large numbers in polynomial time.!1997 - Lov Grover develops a quantum search algorithmwith O("N) complexity

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Factoring

Multiplication Factoring

13 x 17 = 221 221 = 13 x 17

624691 = 89 x 7019

EASY HARD

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Factoring & secrets

number of digits in N

execution time

0 500

1010 years

Factoring is hard

but easy to verify

USED FOR SECURECOMMUNICATION

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Assume someone asks you to factorize 15. Easy 3x5.

For 180=3X3X2X2, average for man, computer almost instant.

With a classical computer that can test for 10.000.000.000 differentfactors per second (equivalent to dozens of workstations together),it takes a few months!!!

Power of Quantum Algorithms.

A quantum computer of a hundred qubits will solve this in a fewSECONDS as 2100~1030numbers can be checked simultaneously!!!

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Computational (super) power

A quantum computer of a few hundred qubits will solve this in a fewminutes!!!

For a 1200-digit long number the time would exceed 15 billionyears i.e., the age of the universe !

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Quantum Cryptography

Fortunately quantum physics does not just eliminate the traditionalcryptosystems but provides for their replacement.

Quantum cryptography where single quantum systems (photons)are used to communicate messages is proved to be fundamentally

unbreakable.

This is due to the nature of quantum systems. They CAN NEVER beobserved without being altered in some detectable way!!!

The evesdroper can be always tracked and the message altered orresend again until secure enough communication is established.

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Quantum Cryptography

Alice Bob

Eavesdropping = measurement

destroying superpositions

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000001010011100101110

111

Wh t ill b th Q t

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What will be the Quantum

Transistor ???

QuantumIntegrated circuit ???

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Possible technologies-Io1.Trapped Ions

IEPIn

nsbruck

Oxfo

rd

Read and write by addressing the ionswith laser fields.

Quantum computer prototypes:

Ions

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Read and writeRead and write with ion qubits

using laser pulses

R d d i i h i bi

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Read and write!Read and write with ion qubits

using laser pulses

!" $% & '$()*+" "&%, "- .*$+" & /*&0"*1 )-12*"34 '*3

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Set of qubits isolated from environment.

Quantum information busto connect qubits. Reliable read-out method.

Essential DichotomyNeed WEAK coupling to

environment to avoiddecoherence, but you also

need STRONG coupling to atleast some external modes inorder to ensure high speed and

reliability.

!" $% & '$()*+" "&%, "- .*$+" & /*&0"*1 )-12*"34 '*3"- )*4430" +$1$"&5-0 $0 "3)60-+-789

7 ) ) 9 :

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7*8 . ,-./)-0 1*02-)$" 9**:(

9#:$ /*8;./

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;'*8 . 19.((#1.9 1*02-)$" 9**:$