By Daniel Stick, Jonathan D' Sterk,

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THE
TRAP
TECHNIQUE
TOWARD A CHIP-BASED QUANTUM COMPUTER

• By Daniel Stick, Jonathan D. Sterk,
• and Christopher Monroe

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Outline

• Introduction (why quantum computer?)
• Bits and Qubits
• Quantum entanglement
• How the ion trap works?
• Quantum logic
• Conclusion

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Outline

• Introduction (why quantum computer?)
• Bits and Qubits
• Quantum entanglement
• How the ion trap works?
• Quantum logic
• Conclusion

4
Introduction
How many atoms per bit ?
ICFO Institut de Ciències Fotòniques,
Barcelona, Spain Institut für Experimentalphysik,
U Innsbruck, Austria
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Introduction

• Quantum computer
• Quantum parallelism--gtfaster

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Outline

• Introduction (why quantum computer?)
• Bits and Qubits
• Quantum entanglement
• How the ion trap works?
• Quantum logic
• Conclusion

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Bits and Qubits

• A one bit memory can store one of the numbers 0
  and 1.  Likewise a two bit memory can store one
  of the binary numbers 00, 01, 10 and 11.  But
  these memories can only store a single number at
  a time.
• Quantum computers providing a quantum
  superposition state allows a qubit to store 0 and
  1 simultaneously.  Two qubits can store all the 4
  binary numbers 00, 01, 10 and 11 simultaneously. 
  Three qubits stores the 8 binary numbers 000,
  001, 010, 011, 100, 101, 110 and 111
  simultaneously.   In theory, with n qubits you
  could be calculating with 2n numbers at once.

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Qubit System

• Quantum dots
• The quantum dot behaves like a large artificial
  atom and can be used as a qubit. A user can
  access individual quantum dots using focused
  laser beams which can flip the electron between
  two discrete energy levels or place it into a
  superposition of the two levels.
• Ion traps
• Individual ions can be trapped using electric and
  magnetic fields. Finely focused lasers are used
  to prepare and inspect individual ions. The
  outer electron of each ion is manipulated to be
  in two different orbits about the nucleus. Each
  ion therefore represents a qubit.

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Outline

• Introduction (why quantum computer?)
• Bits and Qubits
• Quantum entanglement
• How the ion trap works?
• Quantum logic
• Conclusion

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Quantum Entanglement

• Two particles can be linked so that if you
  perturb or measure one, the quantum state of the
  other changes instantly. For instance, you could
  entangle two ions so that their spin states will
  always be opposite to each other. If you measure
  the state of the first as a 1, the second will
  instantly become a 0.

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Outline

• Introduction (why quantum computer?)
• Bits and Qubits
• Quantum entanglement
• How the ion trap works?
• Quantum logic
• Conclusion

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How an Ion Trap Works
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Type of Ion Traps
A schematic of a trapped ion process
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Outline

• Introduction (why quantum computer?)
• Bits and Qubits
• Quantum entanglement
• How the ion trap works?
• Quantum logic
• Conclusion

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• 1. You must be able to set all the qubits to 0 at
  the start of a calculation.
• 2. You must be able to read the answer when the
  calculation is done.
• 3. The qubits must last long enough to run a
  program of a decent size.
• 4. The computer must be able to carry out the two
  fundamental operations that are necessary to
  perform every quantum computer program.
• 5. The systems basic architecture must be able
  to handle large numbers of qubits.

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Quantum Logic
A pair of qubits in an ion trap repel each
other in a way that makes them act as if they
were two balls connected by a spring. The motion
of the balls and spring, the vibrational state of
the system, contains measurable information that
can be used in quantum computations.
A particular color and polarization of laser
has the effect of forcing a qubit ion to move in
a particular direction, but only if the qubit's
value is 1. This trick is key to implementing the
controlled not (CNOT) gate, a necessary logic
operation for any quantum computer. The operation
maps the result of the CNOT gate onto the
vibrational state. Further laser manipulations
impose the vibrational state onto the target
qubit.
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Outline

• Introduction (why quantum computer?)
• Bits and Qubits
• Quantum entanglement
• How the ion trap works?
• Quantum logic
• Conclusion

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Conclusion

• There are still many issues and potential of
  quantum computer.
• Quantum computer may make a big change toward
  humans civilization.

Reference http//www.spectrum.ieee.org/aug07/5378
Nature Physics, January 2006, pp. 3639.