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Harnessing Quantum Weirdness: Quantum Computing with Cold Atoms US National Security Agency US Advanced Research and Development Activity US Army Research Office National Science Foundation Paul C. Haljan University of Michigan October 2004 FOCUS Michigan FOCUS Center ENIAC (1946) The first solid-state transistor (Bardeen, Brattain & Shockley, 1947) Moore’s Law Source: Intel The Ant and the Pentium ~100 million transistors INTEL Pentium 4 transistor Size of an atom ~ 0.1nm “There's Plenty of Room at the Bottom” (1959 APS annual meeting) 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…” The Golden Rules of Quantum Mechanics 1. Quantum objects are waves and can be in states of superposition…… |1 “quantum bit”: a|0 + b|1 |0 2. …… as long as you don’t look! |0 a|0 + b|1 or |1 quantum measurement flipping a coin Michigan A quantum computer hosts quantum bits which can store superpositions of 0 and 1 classical bit: 0 or 1 quantum bit: a|0 + b|1 Examples of “qubits” photons V N particle spins hn H atoms S S N Benioff (1980) Feynman (1982) GOOD NEWS… quantum parallel processing on 2N inputs Example: N=3 qubits f(x) = a 0 |000 + a 1 |001 + a 2 |010 + a 3 |011 +a 4 |100 + a 5 |101 + a 6 |110 + a 7 |111 …BAD NEWS… Measurement gives random result e.g., |101 f(x) …GOOD NEWS! quantum interference quantum logic gates depends on all inputs (But ask your question carefully) Some quantum logic gates: quantum |0 |0 + |1 NOT gate: |1 |1 - |0 |0 |0 |0 |0 quantum |0 |1 |0 |1 XOR gate: |1 |0 |1 |1 |1 |1 |1 |0 “Classical” NOT 01 10 e.g., (|0 + |1)|0 |0|0 + |1|1 superposition entanglement Quantum Entanglement: Einstein’s “Spooky action-at-a-distance” “superposition” or “entangled superposition” or Schrodinger cat “experiment” see E. Schrödinger (1935) Quantum object - Radioactive particle. 50% probability of decay in 1 hour. Decay causes vial of cyanide to be broken Classical object: cat Can the cat be alive and dead at the same time? Schrodinger cat McEvoy & Zarate Deutsch (1985) Shor (1994) fast number factoring Grover (1996) fast database search # articles on “Quantum Information” or “Quantum Computing” 500 400 300 200 Nature Science Phys. Rev. Lett. Phys. Rev. 100 0 ……. Quantum computer hardware requirements 1. Must make states like |000…0 + |111…1 2. Must measure state with high efficiency • strong coupling to environment • strong coupling between qubits • weak coupling to environment (can’t look!) Electromagnetically Trapped Atoms 0.3 mm Ions Lightning Neutral Positively charged ion (missing an electron) Demo – Tesla coil Ion trapping basics Applied voltages generate trapping electric fields V RF atomic beam e- Trap electrodes photon-counting camera (or PMT) resonant light Trapping charged ions with electric force fields. Constant fields won’t work! The electric field “fluid” will always squirt out in some direction pushing the ion away. One solution: Dynamic (time changing) fields! Demo – rotating saddle movie |1 |0 2 mm 2 cadmium ions Cd+ dc rf dc dc rf dc “Perfect” quantum measurement of a single atom state |1 state |0 laser laser atom fluoresces 108 photons/sec atom remains dark Laser Atom radio in tune with laser radio station Atom radio not tuned to laser radio station Coherent transitions between |0 and |1 LASER |0 |0 + |1 |1 ……… Coherent transitions between 0 and 1 in a single 111Cd+ qubit t |0 + |1 Data taken with a single ion 1 Prob(1) |0 0.5 averaged data |1 0 0 100 200 t (ms) 300 400 The invisible forces between ion qubits ….are the “wires” connecting them 40Ca+ Collective vibrations of the ion crystal Demo – coupled pendula (R. Blatt, Univ. Innsbruck) Collective motion: the “quantum data bus” state of motion |rest |0 |0 + |1 |0 |0 |1 laser |rest + |moving |0 |0 |0 |0 |1 Trapped Ion Quantum Computer laser cool to rest j k map jth qubit to collective motion laser j k flip kth qubit if collective motion laser j k map collective motion back to jth qubit laser Cirac and Zoller, Phys. Rev. Lett. 74, 4091 (1995) Boris Blinov ANN ARBOR MICHIGAN First direct observation of entanglement between a single atom and single photon. Michigan 2004 Four ion-qubit quantum logic gate NIST 2000 Deterministic quantum teleportation 3 ion-qubit expt. NIST, Innsbruck 2004 High Fidelity Cadmium Quantum Computing Schrodinger’s other cat Cd+ quantum bits Cadmium ~40nm |0 |1 0 here 1 there Kathy-Anne Brickman, Louis Deslauriers, Patty Lee PCH “Tee” junction Winfried Hensinger Mark Acton Dave Hucul Rudy Kohn Dan Stick entangle shuttle 400 microns entangle “Quantum Pentium” …. Dan Stick Martin Madsen Winfried Hensinger Keith Schwab (LPS/UMd) 6mm 40mm Andrew Cross, Ike Chuang (MIT) A “quantum modem” linking quantum computers coincident photon detection BS Ypsilanti Ann Arbor Remote ion-ion entanglement B. B. Blinov, D. L. Moehring, L.-M. Duan, and C. Monroe, Nature 428, 153 (2004) PI: Chris Monroe Postdocs: Boris Blinov, Paul Haljan, Winfried Hensinger Graduate students: Mark Acton, Kathy-Anne Brickman, Louis Deslauriers, Patty Lee, Jie Li, Martin Madsen, David Moehring, and Daniel Stick. Not Shown: Steve Olmschenk Undergraduate students: David Hucul, Rudy Kohn Jr. Not Shown: Mark Yeo http://iontrap.physics.lsa.umich.edu/ Thanks! Prof. Tim Chupp Prof. Chris Monroe Prof. Jens Zorn Jeremy Herr Kate Logan Angie Milliken Carol Rabuck Kathy Richards Mark Kennedy Warren Smith Harminder Singh Sandhu