Quantum Information Science A Second Quantum Revolution Christopher

Quantum Information Science: A Second Quantum Revolution Christopher Monroe 18 56 Joint Quantum Institute University of Maryland Department of Physics www. iontrap. umd. edu

Joint Quantum Institute Quantum science for tomorrow’s technology

Computer Science and Information Theory Charles Babbage (1791 -1871) mechanical difference engine Alan Turing (1912 -1954) universal computing machines Claude Shannon (1916 -2001) quantify information: the bit

ENIAC (1946)

The first solid-state transistor (Bardeen, Brattain & Shockley, 1947)

Source: Intel

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

Quantum Mechanics: A 20 th century revolution in physics • • Why doesn’t the electron collapse onto the nucleus of an atom? Why are thermodynamic anomalies in materials at low temperature? Why is light emitted at discrete colors? . . Erwin Schrödinger (1887 -1961) Albert Einstein (1879 -1955) Werner Heisenberg (1901 -1976)

The Golden Rules of Quantum Mechanics 1. Quantum objects are waves and can be in states of superposition. “qubit”: [0] & [1] 2. Rule #1 holds as long as you don’t look! [0] & [1] or [0] [1]

Most of 20 th century quantum physics concerned with rule #1: • Wave mechanics • Quantized energy • Low temperature phenomena e. g. , superfluidity, BEC • Quantum Electrodynamics (QED) e. g. , magnetism of the electron: ge = 2. 00231930439 (agrees w/ theory to 12 digits) • Nuclear physics • Particle physics

A new science for the 21 st Century? Information Quantum Mechanics 20 th Century Theory Quantum Information Science 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)

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

# articles mentioning “Quantum Information” or “Quantum Computing” 2000 1500 1000 Quantum Computers and Computing Nature Science Phys. Rev. Lett. Phys. Rev. Institute of Computer Science Russian Academy of Science ISSN 1607 -9817 0 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 500

…GOOD NEWS! quantum interference depends on all inputs quantum logic gates quantum [0] + [1] NOT gate: [1] - [0] quantum [0] XOR gate: [0] [1] [1] [0] [1] e. g. , ([0] + [1]) [0][0] + [1][1] superposition entanglement [0]

Ψ = [↑][↓] - [↓][↑] John Bell (1964) Any possible “completion” to quantum mechanics will violate local realism just the same

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

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

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

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

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

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

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

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

Trapped Atomic Ions seven Yb+ ions ~2 mm NIST-Boulder (D. Wineland) U. Innsbruck (R. Blatt) U. Maryland & JQI (C. M. )

171 Yb+ qubit 1 Probability Electronic Excited State (t ~ 8 nsec) [ ] 0 0 5 10 15 20 25 # photons collected in 100 ms [ ] Hyperfine Ground States ~GHz [ ] “bright”

171 Yb+ qubit 1 Probability | 99. 7% detection efficiency Electronic Excited State (t ~ 8 nsec) | 0 0 5 10 15 20 25 # photons collected in 100 ms [ ] Hyperfine Ground States ~GHz [ ] “dark”

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

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

1 mm

Ion Trap Chips NIST-Boulder Au/Quartz Maryland/LPS Ga. As/Al. Ga. As Lucent/MIT Al/Si/Si. O 2 Sandia W/Si

Teleportation of a single atom from here… to here…

we need more qubits. .

Single electron quantum dots Albert Chang (Duke Univ. )

Phosphorus atoms in Silicon qubit stored in 31 P nuclear spin (31 P: spin) (28 Si: no spin) Si lattice B. Kane, Nature 393, 133 (1998) • LPS/U. Maryland • Los Alamos • entire country of Australia

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

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

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

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

N=1 N=1028

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

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