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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