1. As if computers weren’t fast enough already…
Quantum Computers
As if computers weren’t fast enough already…

2. Brief Outline Introduction – What is a quantum computer?
Differences from classical computers
Power(speed,efficiency, etc.)
History
Problems
Conclusion

3. What is a quantum computer?
Computer using the laws of quantum mechanics
Utilizes physical phenomena
Quantum interference
Superposition
May seem to defy logic
Mostly theoretical – many of the ideas cannot work due to quantum nature
Photon Split?
No!
->
Classical
Idea
Quantum
Idea

4. The difference between classical and quantum computers
Bits – storage in 0’s and 1’s
Uses Boolean logic gates to manipulate bits
Macroscopic physical storage
Charge, magnetization, etc.
Governed by the same laws as everyday phenomena
Can only manipulate one piece of data at a time
Quantum
Qubits – storage in 0’s, 1’s, or a superposition of both.
Executes quantum gates to act as unitary transformations on qubits
Uses quantum laws which differ greatly from everyday phenomena
Can manipulate many pieces of data at once

5. Computing speed and efficiency
Qubit can hold as many values at once as a bit has range to hold
3 bits: can hold one number up to 8
3 qubits: can hold 8 numbers up to 8
Can perform many computations at the same time, as opposed to performing them one at a time
Factoring, as an example
Peter Shor, AT&T Bell Laboratories, New Jersey

6. History
Idea developed from the idea of elements being small enough to behave on the quantum level
1982 – Feynman comes up with idea for computations. Says quantum computers can be used for quantum simulations.
1985 – Duetsch realized Feynman’s assertion could lead to a general purpose computer and published a paper that showed how.
1994 – Shor circulates a preprint of a paper showing how quantum computers could solve many mathematical problems many times faster than classical computers (namely factorization).
1995 – Theory of quantum error correction
1998 – Researchers at Los Alamos National Laboratory and MIT led by Raymond Laflamme spread a qubit across three nuclear spins in each molecule of a liquid solution of alanine or trichloroethylene molecules – possible with NMR (nuclear magnetic resonance)
Spread makes it harder to corrupt – can indirectly measure decoherence and compare spin states
Present -

7. Problems
Decoherence – tendancy of quantum computer to decay as it interacts (entangles) with the outside environment
Qubits cannot be directly measured – lose superposition and change to 0 or 1 when attempted
May try to set up an algorithm to cycle through qubits after they are manipulated, narrowing down the possible answers, until the probability of the right answer showing up is close to 100%
Phase coherence may be used for error correction
Architecture is too complicated, large, or expensive
World is too dependent on current computer systems
Ideas are fundamentally more difficult than classical computers

8. Conclusion Quantum computer research is making breakthroughs
We may someday have quantum computers for generic use
Quantum computers could provide faster or better methods of doing most anything (encryption, as an example)
There are too many problems for such breakthroughs to occur in the near future
For those of you who have taken Quantum A & B: Quantum physics IS practical for something in our everyday lives – your nights and weekends spent on homework were not spent in vain!

9. References