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Quantum Computation Using Optical Lattices

Quantum Computation Using Optical Lattices. Ben Zaks Victor Acosta. Physics 191 Prof. Whaley UC-Berkeley. Contents. Standing Wave Light Field Egg Crate Potential Atom Cooling Gates and Qubits. 1D Optical Lattice. 2 Linearly Polarized Light Waves. σ +.

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Quantum Computation Using Optical Lattices

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  1. Quantum Computation Using Optical Lattices Ben Zaks Victor Acosta Physics 191 Prof. Whaley UC-Berkeley

  2. Contents • Standing Wave Light Field • Egg Crate Potential • Atom Cooling • Gates and Qubits

  3. 1D Optical Lattice 2 Linearly Polarized Light Waves...

  4. σ+ …or 2 Circularly Polarized Standing Waves! σ- 1D Optical Lattice

  5. Atom in a Light Field: AC-Stark Shifts Electric Dipole Hamiltonian Time Dependent Schroedinger Equation Choose Rotating Frame: Unitary Transformation Finally

  6. Example: Two-Level System

  7. Example: J=1/2 J=3/2

  8. -1 -2 -3 Periodic Spatially-Varying Optical Trap

  9. Cooling in Optical Lattices Optical Molasses and Magneto-Optical Traps • Six lasers tuned slightly below the resonance frequency of atoms being trapped • Atoms moving towards lasers see frequencies closer to resonance • Atoms moving towards lasers absorb more momentum • Magnetic field gradient creates Zeeman splitting to further trap atoms • Can cool to ~1 microKelvin

  10. Cooling in Optical Lattices Sisyphus Cooling • Atoms with enough energy can climb out of the well • Atoms will be optically pumped from the higher energy ground state (red line) • Spontaneous emission will drop the atom into the lower energy ground state (blue line) • The atom loses more energy than it gains, so it is cooled

  11. Quantum Computation An Array of Qubits • Optical lattices contain neutral atoms, ions or polar molecules as qubits • Electric dipoles of these particles are qubits aligned with or against an external field • Qubits are entangled by the dipole-dipole interaction • Need strong coupling between qubits but weak coupling with environment

  12. Quantum Computation Some Current Research • Prof. DeMille uses polar molecules as qubits at Yale • An electric field gradient allows for spectroscopic addressing of individual qubits • Microwave laser pulses can be used as single and two-qubit gates • Coupling effects can be eliminated by “refocusing”

  13. Quantum Computation Some Current Research • Prof. Deutsch et al. use neutral atoms in far-off resonance optical lattices as qubits at the University of New Mexico • Neutral atoms have weak dipole-dipole interactions but are also very weakly coupled to the environment • Polarization is rotated to bring atoms together • Once together, laser pulses set to specific resonances will only allow specific transitions, and these can be utilized as gates

  14. Thank you to the following websites for their resources • http://quaser.physics.lsa.umich.edu/projects/lattice/ • http://web.arizona.edu/~lascool/research.html • http://nobelprize.org/physics/laureates/1997/illpres/ • http://www.yale.edu/physics/research/atomic.html • http://physics.nist.gov/Divisions/Div842/Gp4/lattices.html

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