Ion Trap Quantum Computer

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Ion Trap Quantum Computer
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Two Level Atom as a qubit
Electron on lower orbit
Electron on higher orbit
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Ion Trap Quantum Computer
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Ion Traps
Linear ion trap

• Ions in a radio frequency trap interact by
  exchanging vibrational excitations. Each ion can
  be controlled by a polarized, properly focused
  laser beam.
• Picture shows the electrode structure.
• The electrode is 1mm thick.

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Linear ion trap computer
Research in NIST
Laser pulses
electrodes
ion
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Quantum CNOT gate on beril ion in the trap
Linear ion trap
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Silicon Based Quantum Computer
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Optical Quantum Computer
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What about scaling?

• 1-7 qubits using NMR technology
• 1-2 qubits using ion traps
• 1-2 qubits using various other quantum
  technologies
• Scaling is very hard!
• Is the problem technical or fundamental?

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Technical or Fundamental?

• Noise, decoherence, imprecision are detrimental
• Similar problems exist in classical systems
• Theory of linear error correction and fault
  tolerant computing can be generalised to the
  quantum setting (Shor, Steane, etc.)
• Using reasonable physical models, there exist
  fault-tolerant schemes for scalable quantum
  computing

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Quantum Circuits

• Quantum Error-Correction Circuit
• Problem State ?? a0? b 1? is degraded by
  noise

• Solution Encode in a suitable EC code such as the
  5-bit code
• 0? 00000? 11000? 01100? 00110?
  00011? 10001? 10100? 01010?
  00000? 10010? 01001?
• 11110? 01111? 10111? 11011?
  11101?
• 1? 11111? 00111? 10011?

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Summary
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Summary

• Quantum Computers are a natural generalisation of
  classical computers
• Quantum algorithms Factoring, Discrete log,
  Hidden Subgroup, Hidden Affine Functions,
  Searching, Counting
• Small implementations exist
• Scaling is difficult, but seems to be a
  technological (not fundamental) problem

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References

• 1 Chuang, Issac and Gershenfeld, Neil Quantum
  Computing With Molecules Scientific American
  June 1998.
• 2 Hey, Anthony Possible Technologies for
  Quantum Computers May 1998 http//www.ecs.soton.
  ac.uk/ajgh/quantrep.html
• 3 Nuclear Magnetic Resonace Quantum Computers
  http//www.qubit.org/research/NMR/index.html
• Mar 2001.
• 4 Quantum Computing Experiment At Los Alamos
  http//p23.lanl.gov/Quantum?qcexper.html
• Jan 2001.
• 5 QUIC Milestones http//theory.caltech.edu/qu
  ic/milestones.html
• Mar 2001.
• 6 Simple Quantum Gates http/www.qubit.org/intr
  os/comp/inset2.html
• Mar 2001.
• 7 Waldtrop, M Quantum Computing Technology
  Review May/June 2000.

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Physical Implementation NMR

• Five-qubit computer (contd.)
• Molecule with 5 flourine atoms
• whose spins implement the qubits
• Experimental 5-qubit circuit to find the order of
  a permutation

Quantum Fourier Transform
measurements