from imaginary experiments to quantum information

8/19/2019 From imaginary experiments to quantum information

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Luis A. Orozco

St. Mary’s College, March 2013.

www.jqi.umd.edu

From imaginary experiments to

quantum information


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With special thanks to:

William D. Phillips

Howard J. Carmichael

Steven L. RolstonPablo Barberis Blostein

Ivan H. Deutsch

Work supported by

National Science Foundation


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time

s p e e d

Classical World


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50 micrometers

10,000X


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10,000X

The world becomes discrete … it comes in quanta

Quantum World


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It all started in the 19th century


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• Oct. 7, 1900

" # ,T ( ) =8$ h#

3

c3

1

eh# / kT

%1

Coffee and Cake with the Rubens

• The birth of quantum theory“an act of desperation…I had to obtain a positive result

under any circumstances and at whatever cost”

Max Planck


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• 1905 the “photon”, is the quantum oflight

Albert Einstein


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• Radioactivity has been around for 15 years.

1911Rutherford discovers

the nucleus

“use alpha particles tobombard gold atoms and

look at how they bounceback. Some come back

almost in the sametrajectory implying a verysmall but highly

concentrated group ofpositive charges.”

Ernest Rutherford


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1913 visit to Rutherford

Niels Bohr


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• 1920’s –Quantum Theory – Heisenberg

– Schrodinger

–

Dirac

– De Broglie

– Pauli

–

Born


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•

Quantum Theory

– Described by wavefunction

–

Describes probability, not “reality”. This is the source

of many discussions. –

Uncertainty principle – two properties (such asposition and velocity) cannot simultaneously beknown to arbitrary accuracy

–

Wave-particle duality – things can be wavelike orparticlelike

–

Principle of superposition

–

Wavefunction collapse when measured


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An electron is like a spinning top.

The spin can

only point up……or down

AND it can be BOTH up and down at

the same time!SUPERPOSTION:

" = 1

2

(# + $ )


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Fred Alan Wolf, "Taking the Quantum Leap"(Harper & Row, San Francisco, 1981)

How can something be “in two places at the same time”?

This “cube” could be


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or



this


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or



this


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and


but

this this

No classical analog to superposition exists.


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• Quantum Mechanics

–

The most successful physical theory – Tested to parts in a trillion

– Never proven wrong or incomplete*

* Except it is not yet compatible with general relativity (gravity).


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• Quantum Mechanics enabled the Information

Age – The transistor (1948)

– Microelectronics

–

Lasers (1960) – Magnetic storage


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–

Quantum mechanics has given us a superb

understanding of chemistry and materials


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Einstein was not happy

with the consequences of

quantum mechanics


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Schroedinger reacted to

the questions of Einstein

with the termEntanglement.

This is where quantum

mechanics gets weird.


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If blue is measured V, red MUST be H

+


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David Wineland Nobel Lecture


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Correlations


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If blue is measured -45, red MUST be +45

+


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The dialogue between Bohr and Einstein was long

and many times included imaginary experiments

(gedanken) that quantum mechanics alwaysexplained


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Bohr drew thisimaginary experiment

to study the relation

between time andenergy with Einstein


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• 1964 John Bell:

– Is entanglement

measurable? – If we assume reality

and locality , this is not

consistent with the

results of QM

– tested numerous times


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• Bell theorem on 1964 implies that

You must give up something:

– Objective Reality

–

Locality (causality)


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• Quantum mechanics is a theory about

our (incomplete) knowledge of nature, not

of nature itself.

And that’s all there is.


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The end of Moore’s Law…

“In terms of size [of transistor] you can see that we are

approaching the size of atoms which is a fundamental

barrier…We have another 10 to 20 years ….” G. Moore

2009.


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Put weirdness of quantum mechanics to

work…

A second quantum revolution…


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David Wineland, Nobel Lecture


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Experiments manage to trap work individual matter quanta

starting in the 70s.

Trapped electrons and ions (Dehmelt and Wineland)Quantum jumps of electrons between levels in an ion

(Dehmelt, Toshek, Wineland)

Hans Dehmelt David Wineland

“Monoelectron Oscillator ” D Wineland P Ekstrom


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Monoelectron Oscillator, D. Wineland, P. Ekstrom,

and H. Dehmelt, Phys. Rev. Lett. 31, 2179 (1973)


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Experiments manage to trap and work with individual light

quanta starting in the 80s.

Trapped photons (Walther and Haroche)Micro-laser, Cavity Quantum Electrodynamics.

Serge HarocheHerbert Walther


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Quantum Mechanical formulation based on Quantum Jumps

(Zoller, Dalibard, Carmichael)

Peter Zoller Jean Dalibard Howard Carmichael


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“Observation of Quantum Jumps in a Single Ion,” J. C.

Bergquist, Randall G. Hulet, Wayne M. Itano, and D. J. Wineland

Phys. Rev. Lett. 57, 1699 (1986)


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Serge Haroche, Nobel Lecture


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Serge Haroche, Nobel lecture


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Two trapped ions (JQI Monroe Lab)


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Terraciano et al Nature Physics 2009


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Bennett

(1982)

Landauer

(1961)

Benioff

(1985)

Reversible computing (thermodynamics)

Deutsch

(1985)

Model of a universal quantum circuit

Feynman

(1982)

Quantum simulations

Quantum Information


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Quantum

MechanicsInformation

Science

Quantum Information Science

20th Century

21st Century

A New Science!


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Classical Bits vs Quantum Bits

Classical Bit: 0 or 1; or

Quantum Bit (Qubit):

Can be a quantum superposition of 0 and 1

# =

qubit +


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But 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 to 7

a | 000 + b | 001 + c | 010 + d | 011 $ + e | 100 + f | 101 + g | 110 + h | 111 $ • Result:

-- Classical: one N-bit number

-- Quantum: 2N (all possible) N-bit numbers

0 1

Quantum Mechanically, a register of 3 entangled

qubits can store all of these numbers in superposition:

1


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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


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CRYPTOGRAPHY

Virtually all public key cryptographic systems

rely on the difficulty of factoring large numbers…

If you can figure out how to do this, your credit

card is not safe… and neither are governmentcommunications, financial transactions,personal information…


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12301866845301177551304949583849627207728535695

9

53347921973224521517264005072636575187452021997

8

64693899564749427740638459251925573263034537315

4

826850791702612214291346167042921431160222124047

9274737794080665351419597459856902143413


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12301866845301177551304949583849627207728535695

9

53347921973224521517264005072636575187452021997

8

64693899564749427740638459251925573263034537315

4

826850791702612214291346167042921431160222124047

9274737794080665351419597459856902143413

2 years 1000 computers


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12301866845301177551304949583849627207728535695953347921973224521517264005072636575187452021997864693899564749427740

6384592519255732630345373154826850791702612214291346167042

9214311602221240479274737794080665351419597459856902143413

1230186684530117755130494958384962720772853569595334792197

32245215172640050726365751874520219978646938995647494277406384592519255732630345373154826850791702612214291346167042

9214311602221240479274737794080665351419597459856902143413

4 years 1,000,000,000,000 computers


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The Quantum Computer

• 1994 Peter Shor

•

With Quantum Mechanics, it ispossible to factor an N-digitnumber in ~ N3 steps… muchfaster than the exponentially largenumber of steps that we neednow.


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Quantum computing:• Universial machine (Shor’s algorithm)

• Quantum simulation

Quantum cryptography:

• Key distribution (QKD)

• Secret sharing

Quantum Communication:

• Channel capacity

• Distributed computing

Quantum metrology

• Precision sensors


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A quantum computer (if we can make one) would be more

different from our current digital computers than our computers

are from the ancient abacus.

A general-purpose quantum computer is years away, but

along the way we will be exploring some of the most

important outstanding questions in science.


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Quantum Mechanics and Information Science have beentwo of the most important and revolutionary developments

in the XX Century, affecting both science and technology

Quantum mechanics changed the way we think about the

physical world and the nature of reality. It gave us modernelectronics with all its advantages.

Information science changed the way we think about

thinking. They gave us digital information.

They are now merging into Quantum information and we

can only wait a greater revolution.


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Thanks!

from imaginary experiments to quantum information

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