18 56

Quantum Information Science: A Second Quantum Revolution

Christopher Monroe

www.iontrap.umd.edu

Joint Quantum InstituteUniversity of Maryland Department of Physics

Joint Joint QuantumQuantum Institute Institute

Quantum science for tomorrow’s technology

Computer Science and Information Theory

i

k

ii ppH 2

1

log

Alan Turing (1912-1954)universal computing machines

Claude Shannon (1916-2001)quantify information: the bit

Charles Babbage (1791-1871)mechanical difference engine

ENIAC(1946)

The first solid-state transistor

(Bardeen, Brattain & Shockley, 1947)

Source: Intel

“When we get to the very, very small world – say circuits of seven atoms - we have a lot of new things that would happen that represent completely new opportunities for design. Atoms on a small scale behave like nothing on a large scale, for they satisfy the laws of quantum mechanics…”

“There's Plenty of Room at the Bottom”(1959)

Richard Feynman

Albert Einstein (1879-1955)

Erwin Schrödinger (1887-1961)

Werner Heisenberg (1901-1976)

Quantum Mechanics: A 20th century revolution in physics

• Why doesn’t the electron collapse onto the nucleus of an atom?• Why are there thermodynamic anomalies in materials at low

temperature?• Why is light emitted at discrete colors?• . . . .

The Golden RulesThe Golden Rules of Quantum Mechanicsof Quantum Mechanics

2. Rule #1 holds as long as you don’t look!

[1][0]

[0] & [1]

or

1. Quantum objects are waves and can be in states of superposition.

“qubit”: [0] & [1]

• Wave mechanics

• Quantized energy

• Low temperature phenomenae.g., superfluidity, BEC

• Quantum Electrodynamics (QED)

• Nuclear physics

• Particle physics

Most of 20th century quantum physics concerned with rule #1:

tiH

][

][ˆ

e.g., magnetism of the electron:ge = 2.00231930439 (agrees w/ theory to 12 digits)

Quantum

Mechanics

Information

Theory

Quantum Information Science

A new science for the 21st Century?

20th Century

21st Century

What if we store information in quantum systems?

classical bit: 0 or 1 quantum bit: a[0] + b[1]

GOOD NEWS…quantum parallel processing on 2N inputs

Example: N=3 qubits

= a0 [000] + a1[001] + a2 [010] + a3 [011] a4 [100] + a5[101] + a6 [110] + a7 [111]

f(x)

…BAD NEWS…Measurement gives random result

e.g., [101] f(x)

depends on all inputs

quantumlogic gates

…GOOD NEWS!quantum interference

Deutsch (1985)Shor (1994)

Grover (1996)fast number factoring N = pqfast database search

Quantum Computers and Computing

Institute of Computer Science

Russian Academy of Science

ISSN 1607-9817

Quantum Computers and Computing

Institute of Computer Science

Russian Academy of Science

ISSN 1607-9817

0

500

1000

1500

2000

# articles mentioning “Quantum Information”

or “Quantum Computing”

NatureSciencePhys. Rev. Lett.Phys. Rev.

2006

2005

2004

2003

2002

2001

2000

1999

1998

1997

1996

1995

1994

1993

1992

1991

1990

depends on all inputs

quantumlogic gates

[0] [0] [0] [0][0] [1] [0] [1][1] [0] [1] [1][1] [1] [1] [0]

e.g., [0] + [1] [0] [0][0] + [1][1] quantumXOR gate:

superposition entanglement

[0] [0] + [1][1] [1] [0]

quantumNOT gate:

( )

…GOOD NEWS!quantum interference

John Bell (1964)

Any possible “completion” to quantum mechanics will violate local realism just the same

Ψ = [↑][↓] [↓][↑]

[did decay][Alive] + [didn’t decay][Dead]Schrödinger’s Cat (1935)

Entanglement: Quantum Coins

Two coins in aquantum

superposition[H][H] & [T][T]

1 1

Entanglement: Quantum Coins

Two coins in aquantum

superposition[H][H] & [T][T]

0 01 1

Entanglement: Quantum Coins

Two coins in aquantum

superposition[H][H] & [T][T]

0 01 1

0 0

Entanglement: Quantum Coins

Two coins in aquantum

superposition[H][H] & [T][T]

0 01 1

0 01 1

Entanglement: Quantum Coins

Two coins in aquantum

superposition[H][H] & [T][T]

0 01 1

0 01 11 1

Entanglement: Quantum Coins

Two coins in aquantum

superposition[H][H] & [T][T]

0 01 1

0 01 11 11 1

Entanglement: Quantum Coins

Two coins in aquantum

superposition[H][H] & [T][T]

0 01 1

0 01 11 11 10 0. .. .. .

Comments on quantum coins:

1. Doesn’t violate relativity (superluminal communication): no information transmitted in a random bit stream!

2. Application: Quantum Cryptography (a secure “one-time pad”)

+plaintextKEYciphertext

ciphertextKEY

plaintext+

Quantum Superposition

From Taking the Quantum Leap, by Fred Alan Wolf

Quantum Superposition

From Taking the Quantum Leap, by Fred Alan Wolf

Quantum Superposition

From Taking the Quantum Leap, by Fred Alan Wolf

Quantum Entanglement

“Spooky action-at-a-distance” (A. Einstein)

From Taking the Quantum Leap, by Fred Alan Wolf

Quantum Entanglement

“Spooky action-at-a-distance” (A. Einstein)

From Taking the Quantum Leap, by Fred Alan Wolf

Quantum Entanglement

“Spooky action-at-a-distance” (A. Einstein)

From Taking the Quantum Leap, by Fred Alan Wolf

Quantum Entanglement

“Spooky action-at-a-distance” (A. Einstein)

From Taking the Quantum Leap, by Fred Alan Wolf

NIST-Boulder (D. Wineland)U. Innsbruck (R. Blatt)U. Maryland & JQI (C.M.)

Trapped Atomic Ions

~2 m

seven Yb+ ions

171Yb+ qubit

[]

[]

~GHz

HyperfineGround States

ElectronicExcited State( ~ 8 nsec)

“bright”

# photons collected in 100 s0 5 10 15 20 25

0

1

Pro

babili

ty

[]

99.7% detectionefficiency

0 5 10 15 20 25

Pro

babili

ty

# photons collected in 100 s

0

1

|

|

“dark”

[]

[]

~GHz

HyperfineGround States

171Yb+ qubit

ElectronicExcited State( ~ 8 nsec)

•••

01

2[]

•••

01

2

[] ~MHz

Mapping: (a[] + b[]) [0]m [] (a[0]m + b[1]m)

Cirac and Zoller, Phys. Rev. Lett. 74, 4091 (1995)

~GHz

HyperfineGround States

ElectronicExcited State

Cirac and Zoller, Phys. Rev. Lett. 74, 4091 (1995)

Trapped Ion Quantum Computer

Internal states of these ions entangled

1 mm

Ion Trap ChipsLucent/MITAl/Si/SiO2

Maryland/LPSGaAs/AlGaAs

SandiaW/Si

NIST-BoulderAu/Quartz

Teleportation of a single atom from here…

to here…

we need more

qubits..

Albert Chang (Duke Univ.)

Single electron quantum dots

Phosphorus atoms in Silicon B. Kane, Nature 393, 133 (1998)• LPS/U. Maryland• Los Alamos • entire country of Australia

qubit stored in31P nuclear spin

(31P: spin)(28Si: no spin) Si lattice

Superconducting currentsH. Mooij (Delft, Netherlands)

quantized flux qubit states

Superconducting currentsR. Schoelkopf, Michel Devoret Steve Girvin (Yale Univ.)

quantized charge qubit states

Doped impurities in glass

Nitrogen + Vacancyimpurity in diamond

Fluorescence of an array of single impurities in diamond

J. Wrachtrup (Stuttgart)

1. Individual atoms and photonsion trapsatoms in optical latticescavity-QED

2. SuperconductorsCooper-pair boxes (charge qubits)rf-SQUIDS (flux qubits)

3. Semiconductorsquantum dots

4. Other condensed-matterelectrons floating on liquid heliumsingle phosphorus atoms in silicon

scales

works

Quantum Computer Physical Implementations

N=1028

N=1

Quantum

Mechanics

Information

Theory

Quantum Information Science

A new science for the 21st Century?

20th Century

21st Century

Physics ChemistryComputer Science

Electrical EngineeringMathematicsInformation Theory

Postdocs Ming-Shien ChangPeter MaunzDmitry MatsukevichKihwan KimWes CampbellLe LuoQudsia Quraishi

UndergradsGuillermo SilvaAndrew Chew

Collaborators Luming Duan (Michigan)Jim Rabchuk (W. Illinois)Keith Schwab (Cornell)Vanderlei Bagnato (U. Sao Paulo)

Grad StudentsDave HayesRajibul IslamSimcha KorenblitAndrew ManningJonathan MizrahiSteven OlmschenkJon Sterk

http://iontrap.umd.edu