18 56 Quantum Information Science: A Second Quantum Revolution Christopher Monroe Joint Quantum Institute University of Maryland Department of Physics

Joint Quantum Institute Quantum science for tomorrow’s technology

Computer Science and Information Theory Alan Turing ( ) universal computing machines Claude Shannon ( ) quantify information: the bit Charles Babbage ( ) 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 ( ) Erwin Schrödinger ( ) Werner Heisenberg ( ) Quantum Mechanics: A 20 th 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 Rules of Quantum Mechanics of 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 phenomena e.g., superfluidity, BEC Quantum Electrodynamics (QED) Nuclear physics Particle physics Most of 20 th century quantum physics concerned with rule #1: e.g., magnetism of the electron: g e = (agrees w/ theory to 12 digits)

Quantum Mechanics Information Theory Quantum Information Science A new science for the 21 st Century? 20 th Century 21 st 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 2 N inputs Example: N=3 qubits  =a 0 [000] + a 1 [001] + a 2 [010] + a 3 [011] a 4 [100] + a 5 [101] + a 6 [110] + a 7 [111] f(x) …BAD NEWS… Measurement gives random result e.g.,   [101] f(x)

depends on all inputs quantum logic gates …GOOD NEWS! quantum interference Deutsch (1985) Shor (1994) Grover (1996) fast number factoring N = p  q fast database search

Quantum Computers and Computing Institute of Computer Science Russian Academy of Science ISSN Quantum Computers and Computing Institute of Computer Science Russian Academy of Science ISSN

depends on all inputs quantum logic 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] quantum XOR gate: superposition  entanglement [0]  [0] + [1] [1]  [1]  [0] quantum NOT 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 a quantum superposition [H][H] & [T][T] 1

Entanglement: Quantum Coins Two coins in a quantum superposition [H][H] & [T][T] 0 1

Entanglement: Quantum Coins Two coins in a quantum superposition [H][H] & [T][T] 0 1 0

Entanglement: Quantum Coins Two coins in a quantum superposition [H][H] & [T][T]

Entanglement: Quantum Coins Two coins in a quantum superposition [H][H] & [T][T]

Entanglement: Quantum Coins Two coins in a quantum superposition [H][H] & [T][T]

Entanglement: Quantum Coins Two coins in a quantum superposition [H][H] & [T][T]

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”) + plaintext KEY ciphertext KEY 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

171 Yb + qubit [][] [][] ~GHz Hyperfine Ground States Electronic Excited State (  ~ 8 nsec) “bright” # photons collected in 100 s Probability [][]

99.7% detection efficiency Probability # photons collected in 100 s 0 1 | | “dark” [][] [][] ~GHz Hyperfine Ground States 171 Yb + qubit Electronic Excited State (  ~ 8 nsec)

0 1 2 [][] [][] ~MHz Mapping: ( a [  ]  + b [  ]) [0] m  [  ] ( a [0] m + b [1] m ) Cirac and Zoller, Phys. Rev. Lett. 74, 4091 (1995) ~GHz Hyperfine Ground States Electronic Excited State

Cirac and Zoller, Phys. Rev. Lett. 74, 4091 (1995) Trapped Ion Quantum Computer Internal states of these ions entangled

1 mm

Ion Trap Chips Lucent/MIT Al/Si/SiO 2 Maryland/LPS GaAs/AlGaAs Sandia W/Si NIST-Boulder Au/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 in 31 P nuclear spin ( 31 P: spin) ( 28 Si: no spin) Si lattice

Superconducting currents H. Mooij (Delft, Netherlands) quantized flux qubit states

Superconducting currents R. Schoelkopf, Michel Devoret Steve Girvin (Yale Univ.) quantized charge qubit states

Doped impurities in glass Nitrogen + Vacancy impurity in diamond Fluorescence of an array of single impurities in diamond J. Wrachtrup (Stuttgart)

1. Individual atoms and photons ion traps atoms in optical lattices cavity-QED 2. Superconductors Cooper-pair boxes (charge qubits) rf-SQUIDS (flux qubits) 3. Semiconductors quantum dots 4. Other condensed-matter electrons floating on liquid helium single phosphorus atoms in silicon scales works Quantum Computer Physical Implementations

N=10 28 N=1

Quantum Mechanics Information Theory Quantum Information Science A new science for the 21 st Century? 20 th Century 21 st Century Physics Chemistry Computer Science Electrical Engineering Mathematics Information Theory

Postdocs Ming-Shien Chang Peter Maunz Dmitry Matsukevich Kihwan Kim Wes Campbell Le Luo Qudsia Quraishi Undergrads Guillermo Silva Andrew Chew Collaborators Luming Duan (Michigan) Jim Rabchuk (W. Illinois) Keith Schwab (Cornell) Vanderlei Bagnato (U. Sao Paulo) Grad Students Dave Hayes Rajibul Islam Simcha Korenblit Andrew Manning Jonathan Mizrahi Steven Olmschenk Jon Sterk